Dissertations / Theses on the topic 'Plant Physiology'

Thesis (D. Sc.)--Faculty of Science, University of Adelaide, 1990.
Published works [representing] original research conducted during the various phases of [his] academic development--Pref. Includes bibliographical references.

Electrical Impedance Spectroscopy (EIS) is a relatively new method applied to food quality assessment. EIS allows relatively inexpensive assessment, is fast, easy to operate and non-invasive. It has been adopted for investigation of fundamental electrical properties of plant tissues. Although the applications of EIS for food quality determination have been reported previously, the analytical relationships between electrical impedance properties and quality criteria have not yet been fully developed. Further exploration is thus important in acquiring more data on electrical impedance characteristics of fruits and vegetables and researching new approaches for determination of their quality. This dissertation aims to investigate the electrical impedance properties of fruits and vegetables, and explore the relationship between impedance and quality criteria. In particular, the present dissertation outlines experimental research conducted on relationships between impedance properties and fruit tastes as well as the impedance changes observed during ripening process. Impedance measurement to monitor moisture content changes in the progress of drying is also included in this research. In summary, the impedance properties have merits in fruits and vegetables quality assessment. The current used subjective visual inspection and assessment could be replaced by the EIS based approach as it is a more precise measurement of food quality. Further study is required to give this method practical value.

Engineered nanoparticles (ENPs) are increasingly being exploited in a whole range of applications and products due to their novel physicochemistry. Hence it is inevitable that ENPs will enter the environment at an increasing rate over the coming years. The consequential impact following interaction between ENPs with plants and soil microbial communities is of great concern given that they play fundamental roles in the environment and food production. In this study, the impact of capped silver nanoparticles (cAg NPs) on terrestrial (Arabidopsis thaliana and Vicia faba) and aquatic (Lemna minor) plants was investigated. In addition, due to the important role of bacteria in plant survival and growth, this study also assessed the effect of cAg NPs on plant-associated soil microbial community structure. cAg NPs demonstrated varied toxicity towards plants and the associated soil microbes. Whilst the aquatic plants and soil microbial communities investigated in this study were not affected by cAg NPs up to 100 mg/L, for the terrestrial plants evaluated here, cAg NPs above 12 mg/L (specifically 50 and 100 mg/L) demonstrated differential toxic responses. Based on the results of this study, it is clear that concentration, exposure method, released ions, plant species, light intensity and growth mediums are key factors that influence the toxicity of cAg NPs. Although the cAg NP concentrations applied in this study are not yet environmentally relevant, with continued and uncontrolled commercial production of Ag NPs and/or in the event of spillage, such concentrations could occur in the environment in the future. Chlorophyll fluorescence and gas exchange are valuable techniques for analysing the toxicity of ENPs on plants, due to their rapid and reliable results. Further studies in the interactions between plants and Ag NPs are urgently needed and would benefit from the use of different application methods such as aerosolization.

Aphids are economically important pests of glasshouse and temperate crops. By investigating the effects of aphid feeding on plant performance and by understanding the host-pest relationship, novel defence strategies can be devised. The effect of \(Rhopalosiphum\) \(padi\) (the bird cherry-oat aphid) feeding on young \(Hordeum\) \(vulgare\) (barley) plants was investigated. Particular emphasis was placed on changes within the sieve element (SE) because aphids are phloem-feeding insects. Aphid infestation significantly reduced host plant growth rate. High performance liquid chromatography showed a local elevation of leaf calcium levels in infested leaves. Calcium, sulphate and magnesium levels were all elevated systemically by aphid feeding, whilst nitrate levels decreased. Aphid feeding increased the duration of phloem sap exudation from severed stylets but did not alter exudation rate. Electrical penetration graph studies demonstrated that the duration of SE sap ingestion was reduced, and the time aphid stylets spent in pathway through the leaf increased, on pre-infested plants. The time taken for aphids to locate the SE did not increase, however, suggesting that the inhibitory effect was phloem-localised. In an attempt to elucidate the transcriptomic response to aphid attack, microarrays were performed on infested and uninfested barley plants. Gene expression changes in the first and second leaves were compared to determine the local and systemic effects, respectively. The differentially expressed genes have putative roles in defence, hormone signalling, cell wall remodelling, metabolism, transport and regulation of transcription and translation. The general response was a local suppression and systemic induction of plant defences.

The hexagons on a pineapple contrast with the ribs observed, for example, on pumpkins or saguaro cacti. This dissertation demonstrates how these various configurations, and also the related patterns of phyllotaxis (the arrangement of leaves into whorls or spirals) can be understood as the energy-minimizing buckling pattern of a compressed shell (the plant's tunica) on an elastic foundation. The key new idea is that the elastic energy is minimized by special triads or sequences of triads of periodic deformations whose local wavevectors add to zero. Although triad configurations arise from a variety of microscopic mechanisms in natural and laboratory systems, we show that the particular choices of wavevectors that are observed on plants arise in a nontrivial way from properties specific to a mechanical model. Furthermore, the theory predicts correlations between types of phyllotaxis and shapes of plant surface configurations and suggests experiments that can further test the mechanical theory of plant pattern formation. The dissertation concludes with a derivation of Cross-Newell equations governing pattern formation far from onset in nonisotropic systems and in systems with hexagonal planforms.

Salad tomatoes represent an important vegetable crop within Australia. However, the costs of both materials and labour involved in providing this crop with artificial support, in the form of trellising or staking, is high. This project examined the feasibility of using the plant growth regulator, paclobutrazol, as an aid to crop grown without trellising or staking under coastal conditions. Initially a rate of 4 mg plant-, applied as a soil drench 1, 15, 29, 47 or 57 days after transplanting were compared with non-treated plants under glasshouse conditions. The application of paclobutrazol 1 day after transplanting (DAT), and to a lesser extent 15 DAT. profoundly changed growth while later applications (29, 47 or 57 DAT) had little effect. This sensitivity of young tomato plants to paclobutrazol was confirmed in a field trial where 5 rates (nil, 6.25, 12.50, 25.00 and 50.00 g a.i. ha-1) were applied at one of three application times (12, 40 or 60 DAT). Paclobutrazol only effected growth and physiology. when applied at the earliest time while later applications did not appreciably effect salad tomatoes regardless of rate. It was postulated that salad tomatoes remain sensitive to paclobutrazol up to the event of floral initiation. When applied early the highest rate tested produced the most profound changes and there was no evidence of residual effects on a gucceeding lettuce crop. though later applications did cause a slight stimulatory effect to lettuce dry matter accumulation. It was concluded that paclobutrazol was unlikely to cause residual effects to succeeding crops when applied to tomatoes during their sensitive stage and at rates within those tested. A further field experiment tested in more detail the effects of this compound on growth and some aspects of physiology. Paclobutrazol was found to inhibit several important plant characters, viz: height, leaf and stem dry matter accumulation and leaf areas. Conversely it stimulated the partitioning of assimilate to leaves, specific leaf weights, net photosynthesis on a leaf basis, net assimilation rate and water use efficiency on a gas exchange basis. However the stimulatory and inhibitory effects appear to cancel each other out such that treated and untreated plants had similar crop growth rates and fruit yields. Hence, these studies do not present evidence suggesting that this compound has a role to play as an aid to unsupported semi-determinate salad tomato crops, as no yield benefit was conferred.

This study investigated the use of optical remote sensing for estimating leaf and canopy scale light use efficiency (LUE) and carbon exchange. In addition, a new leaf level model capable of predicting dynamic changes in apparent reflectance due to chlorophyll fluorescence was developed. A leaf level study was conducted to assess the applicability of passive remote sensing as a tool to measure the reduction, and the subsequent recovery, of photosynthetic efficiency during the weeks following transplantation. Spectral data were collected on newly planted saplings for a period of 8 weeks, as well as gas exchange measurements of LUE and PAM fluorescence measurements. A set of spectral indices, including the Photochemical Reflectance Index (PRI), were calculated from the reflectance measurements. A marked depression in photosynthetic rate occurred in the weeks after outplanting followed by a gradual increase, with recovery occurring in the later stages of the experimental period. As with photosynthetic rate, there was a marked trend in PRI values over the study period but no trend was observed in chlorophyll based indices. The study demonstrated that hyperspectral remote sensing has the potential to be a useful tool in the detection and monitoring of the dynamic effects of transplant shock. Relationships between hyperspectral reflectance indices, airborne carbon exchange measurements and satellite observations of ground cover were then explored across a heterogeneous Arctic landscape. Measurements were collected during August 2008, using the University of Edinburgh’s research aircraft, from an Arctic forest tundra zone in northern Finland as part of the Arctic Biosphere Atmosphere Coupling at Multiple Scales (ABACUS) study. Surface fluxes of CO2 were calculated using the eddy covariance method from airborne data that were collected from the same platform as hyperspectral reflectance measurements. Airborne CO2 fluxes were compared to MODIS vegetation indices. In addition, LUE was estimated from airborne flux data and compared to airborne measurements of PRI. There were no significant relationships between MODIS vegetation indices and airborne flux observations. There were weak to moderate (R2 = 0.4 in both cases) correlations between PRI and LUE and between PRI and incident radiation. A new coupled physiological radiative transfer model that predicts changes in the apparent reflectance of a leaf, due to chlorophyll fluorescence, was developed. The model relates a physically observable quantity, chlorophyll fluorescence, to the sub leaf level processes that cause the emission. An understanding of the dynamics of the processes that control fluorescence emission on multiple timescales should aid in the interpretation of this complex signal. A Markov Chain Monte Carlo (MCMC) algorithm was used to optimise biochemical model parameters by fitting model simulations of transient chlorophyll fluorescence to measured reflectance spectra. The model was then validated against an independent data set. The model was developed as a precursor to a full canopy scheme. To scale to the canopy and to use the model on trans-seasonal time scales, the effects of temperature and photoinhibition on the model biochemistry needs to be taken into account, and a full canopy radiative transfer scheme, such as FluorMOD, must be developed.

This work describes the regulation of drought stress responses in Arabidopsis thaliana and adresses the roles of the homeodomain-leucine zipper (HD-Zip) transcription factors in this regulation. The characteristics of ATHB6 and ATHB7, two genes encoding class I HD-Zip transcription factors were analysed.

Expression of ATHB6 and ATHB7 was transcriptionally activated in plants subjected to water deficit or exogenous treatment with abscisic acid (ABA).

Transgenic plants constitutively expressing the ATHB7 gene displayed a delayed elongation growth of the main inflorescence stem after transition to reproductive development. This phenotype is consistent with ATHB7 acting as a negative regulator of growth and development of the elongating stem in response to water availability.

Transgenic abi1-1 mutant plants constitutively expressing the ATHB7 gene displayed a reduced wiltiness as compared to monogenic abi1-1 mutants. These data are consistent with the ATHB7 protein having a central role in the drought stress response, regulating the water balance of the plant, and acting downstream to ABI1. Furthermore, the data is consistent with ATHB7 acting as a positive regulator of the drought stress response.

The ABA-induced expression of the ATHB7 gene displayed a dependence on the phytochrome system, suggesting an interplay between light and osmotic stress signaling in the regulation of the ATHB7 gene.

The effects of extracts from purple nutsedge tubers were determined on the germination, growth, root leakage, water status, and photosynthesis of an Upland cotton, DPL 5415, and a Pima cotton, Pima S-7. Tubers extracts inhibited secondary root growth of seedlings more than primary root growth. At 500 ppmw, primary root growth was inhibited 44 percent whereas inhibition of secondary root growth was 64 percent. Non-polar extracts were more inhibitory to growth than polar extracts. Cotton plants grown in soil treated with hexane extracts of tubers containing non-polar allelopathic substances also lost electrolytes from their roots indicating an effect on root function. The effects on root function resulted in perturbations to the capacity of the plants to maintain efficient water status. At 250 ppmw of the hexane extract, the plant water potential, the leaf water content, and the leaf osmotic potential decreased from -0.7 to -1.3 MPa, from 89 to 79 percent, and from -0.8 to -1.0 MPa, respectively. In addition, the photosynthetic capacity of cotton was decreased 50 percent in both cotton cultivars in the second and third day after transplanting to soil treated with 62 ppmw of the hexane extracts. Leaf dehydration to below 70 percent relative water content and a reduction of quantum yield was detected in DPL 5415 at 125 ppmw of the hexane extracts. However, Pima S-7 was capable of tolerating higher levels of dehydration and did not show the reduction of quantum yield. Leaf expansion and epicotyl growth were also inhibited by 30 and 37 percent, respectively, by the hexane extracts at 250 ppmw. Purple nutsedge tubers released volatile substances that inhibited growth when trapped and tested on cotton seedlings, and caused root leakage. GC analyses showed that both the hexane extracts of purple nutsedge tubers and the volatile compounds released from the tubers contained substances with retention times that are characteristic of sesquiterpenes. These results demonstrate that purple nutsedge tubers contain allelopathic substances capable of inhibiting the growth of cotton by interfering with membranes of root cells, disrupting water status, and affecting photosynthesis.

Growth of most crop plants (glycophytes) is reduced in saline environments. A few plant species (euhalophytes) not only tolerate, but require salt, and grow optimally in salinities between 100 and 200 mM NaCl. The halophyte Salicornia bigelovii Torr. shows optimal growth in 200 mM NaCl and reduced growth in low saline conditions. In spite of years of research, mechanisms that confer salt tolerance to some plants and sensitivity to others are poorly understood. This research was undertaken to obtain physiological information in an attempt to determine why S. bigelovii requires salt to reach maximum growth. Salicornia seedlings were grown in the greenhouse in aerated nutrient solutions with 5, 200 or 600 mM NaCl. Plants grown in 200 mM NaCl showed optimal growth. Fresh and dry weight of the plants were reduced when grown in 5 and 600 mM NaCl. The main differences in plants grown in 5 and 600 mM NaCl had to do with ion accumulation. These differences in ion accumulation suggested that salt tolerance in Salicornia was established by regulation of ion transport. This was confirmed by studying two primary transport systems in plants grown in 5 or 200 mM NaCl. These transport systems are the H⁺-ATPases on the plasma membrane (PM-ATPase) and the tonoplast (V-ATPase). Higher PM-ATPase (55%) activities were observed in 200 mM NaCl grown plants. Increases in growth and in PM-ATPase activity in Salicornia shoots after exposure to salinity were highly correlated. V-ATPase activity was significantly stimulated in vivo and in vitro (26 and 46%) after exposure to 200 mM NaCl, and this stimulation was Na⁺-specific. Increased V-ATPase activity was consistent with an increased Na⁺ accumulation (45%) compared to plants grown in 5 mM NaCl. Na⁺-stimulation of ATPases may confer salt tolerance in Salicornia by providing the driving force for regulation of intracellular Na⁺ levels. The ATPases provide an increased H⁺ electrochemical gradient across membranes that may be used by the Na⁺/H⁺ exchangers on the plasma membrane and tonoplast. In addition, H⁺ transport across the plasma membrane leads to acidification of the apoplast that is required for cell wall extension and growth. These transport systems need to work in concert for optimal growth and salt tolerance.

Sundays Thicket and Spekboomveld vegetation in the Eastern Cape have experienced intensive and extensive degradation due to over-browsing by domestic stock. The Subtropical Thicket Restoration Project aims to take advantage of the high carbon sequestration potential of Portulacaria afra (Spekboom) and other Thicket species, to rehabilitate degraded Thicket by restoring biodiversity and ecosystem services, create job opportunities and socio-economic upliftment in local communities, and promote the trade of carbon credits generated by planting and „farming‟ with Spekboom truncheons, rather than domestic stock. Plant material (seeds and length of stem) was sourced from the farm Krompoort, outside Uitenhage in the Eastern Cape. The effectiveness of four different rooting media i.e. plain pool filter sand and 1:1 mixtures of pool filter sand with perlite, potting soil and Thicket soil, on the rooting of ten Thicket species, were tested. Species with the greatest percentage strike and mean root length on stem cuttings were succulent species, Crassula ovata (84 percent strike) and Portulacaria afra (97 percent), as was expected. The application of rooting hormone Seradix© No. 3 did not significantly promote cutting strike or increase mean root length in C. ovata and P. afra. Woody canopy shrub species with the greatest cutting strike and mean root length, overall, were Rhigozum obovatum (24 percent), Lycium cinereum and L. oxycarpum (21 percent), and Searsia longispina (19 percent). These species, as well as Grewia robusta (4 percent), are considered „easy-to-root‟ species, or of sufficient functional value in terms of their spinescence, flower and fruit production, and soil-binding capabilities. Very low percentage strike (<1 percent) and mean root length were achieved in Azima tetracantha, Carissa bispinosa and Gymnosporia polyacantha subsp. polyacantha. These species are considered unsuitable for propagation for rehabilitation purposes. Crassula ovata, L. cinereum, L. oxycarpum, P. afra and S. longispina cuttings produced longer roots when planted in Thicket soil, the same having been found in R. obovatum cuttings planted in perlite. Thicket soil was, therefore, best at promoting cutting strike and root growth in „easy-to-root‟ species. Plain pool filter sand was the only medium in which A. tetracantha, C. bispinosa and G. robusta, cuttings rooted, and perlite the only medium in which G. polyacantha subsp. polyacantha cuttings rooted. Potting soil did not promote significant cutting strike or root growth in any of the species tested. Physiological variables i.e. photosynthetic efficiency (chlorophyll a fluorescence, Fv/Fm) and stomatal conductance (mmol H2O m-2 s-1) were measured for ten Thicket species, including Portulacaria afra. Control plants were watered well once a week, and treatment plants were dried out for 30 days, rewatered on the 30th day and their recovery from drought stress monitored for a further 17 days. Species that responded poorly to drought stress were Gymnosporia buxifolia and Putterlickia pyracantha. In addition to Portulacaria afra, species that showed the fastest recovery and resprout after rewatering, were: Crassula ovata, Ehretia rigida, Grewia robusta, Lycium ferocissimum, Rhigozum obovatum and Searsia longispina. These species produced the smallest decline in volumetric moisture content of soil, and had the lowest decline in photosynthetic efficiency and stomatal conductance during simulated drought. Unlike C. ovata and P. afra, which are CAM or C3-CAM switching species, mortality of transplants will most likely be high, if not total, during transplantation, as this study was done at lower light and temperature, and higher humidity levels than experienced at rehabilitation sites. This study has shown that the reintroduction of propagated woody canopy shrubs and trees into degraded Thicket sites does not appear to be a practical or economical method of actively restoring biodiversity to rehabilitation sites. As woody climax species have been shown to return to sites planted with Spekboom truncheons through „natural regeneration‟ within approximately 50 years, future research efforts should focus on optimising restoration site selection and planting techniques in order to maximize carbon sequestration potential of planted truncheons, which will, in the long term, result in an environment that can support regeneration of the biodiversity to something resembling intact Thicket.

The use of chronological age for example, using days after sowing (DAS), or days after germination (DAG) as a time variable may result in the inherent variability between plants resulting in differences which can be large enough to obscure subtle developmental trends that become evident among plants sown at the same time. An alternative to DAS or DAG is the plastochron index (PI), first used by Erickson and Michelini (1957) as a morphological time scale and numerical index; which to according to the authors suggested and represented a more accurate reflection of the developmental status of a plant. The research presented in this thesis was therefore aimed specifically at utilizing the index in qualitative and quantitative analyses, to confirm its usefulness in analyzing and predicting plant growth and development. Specifically this research focused on investigating various morphological and physiological events that together, hopefully, would serve as a template for the prediction of the growth, development and reactions of Pisum sativum L. to different growth conditions. In Chapter 3, the use of the average length of the first pair of leaflets on each node as a suitable parameter for calculating PI in P. sativum is suggested. The results presented in Chapter 3 suggest that plant age is best expressed using the plastochron index, as this reflects the time interval between the initiations of successive pairs of leaflets. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2005) A re-evaluation of plastochron index in peas - a case for using leaflet length. South African Journal of Botany 71: 76-80”. The PI formula developed was subsequently used in this research to conduct qualitative and quantitative investigations of plant growth and development in which all data and observations were related directly to the plastochron index. In Chapter 4, the sink to source transition in Pisum sativum L. leaves at different plastochron ages in nodulating plants was investigated using the phloem-mobile fluorescent marker, 5,6-carboxyfluorescein (5,6-CF). The results demonstrated that young leaves remained strong sinks up until LPI 0, after which sink-source transition occurred up to LPI 1.8 and leaflets transitioned to strong source systems by LPI 2.0. A well-developed cross-connected phloem system between paired leaflets in peas, and the petiole and the stem vascular supply was observed. The data presented in the second part of Chapter 4 suggest that the phloem transport between leaflet pairs is independent of the sink/source state of the leaflets, or of movement along the source to sink gradient. The data support the presence of a modular transport system which may ensure re-allocation and balancing between leaflets of the same physiological age and photosynthetic and transport status, thereby load-balancing the local transport system, before exporting to other younger (sink) regions. The investigation of leaf development using the plastochron index (Chapter 5) revealed that the formation of air spaces in the palisade and spongy mesophyll, one of the preparatory events for transition from sink to source state in developing leaves, occurs between LPI 0 and LPI 1 in pea leaflets. Results of the anatomical and ultrastructural study related to PI are presented in Chapter 5. The density of wall ingrowths in transfer cells of minor veins increased with LPI and appeared to be associated with the probable transition to source state and the related potential increase in the production of assimilates for export. The onset of wall ingrowth development in leaflets at LPI 0 provided evidence that sink-to-source transition commences at LPI 0 in P. sativum. Presumably-functional plasmodesmata as well as a few mature sieve elements were evident in class IV veins in the apical region of young and older leaflets at LPI 0. The number of mature sieve elements per vein however, increased with increasing LPI. Most class V veins were still undergoing division at LPI 0 and their sieve elements did not show signs of maturity until LPI 1. The increase in the number of mature metaphloem sieve elements in young, supposedly importing tissue at LPI 0 to older, supposedly exporting tissues at LPI 2 is evidence of the association between phloem maturation and transition from importing to exporting status. In Chapter 6, I report on the effects of elevated CO[subscript 2] on the growth and leaf development of nodulating and non-nodulating Pisum sativum L var. Greenfeast grown under controlled environment of the same nitrogen (6mM) and nitrogen- free nutrient solution conditions. Shortterm exposure to elevated CO[subscript 2] induced rapid plant growth, irrespective of treatment. However, long-term elevated CO[subscript 2] treatment did not affect rate of leaf appearance (RLA) in nodulated plants, irrespective of mineral N supply but enhanced RLA in non- nodulating plants supplied with mineral N. Supplied N resulted in a significant increase in leaflet elongation rate (LfER) under both ambient and elevated CO[subscript 2], but LfER was not significantly affected by nodulation but was increased by high CO[subscript 2]. This suggested that the growth of nodulating P. sativum L may not be significantly affected under CO[subscript 2] levels as high as 1000 μmol mol[superscript -1]. The data suggest that elevated CO[subscript 2] will enhance canopy size, provided adequate soil N is available and more so in non-nodulating plants. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2004) The effects of elevated CO[subscript 2] and nitrogen availability supersedes the need for nodulation in peas grown under controlled environmental conditions. South African Journal of Botany 70: 816 – 823”. This thesis demonstrates that the similarity in the qualitative analyses results obtained from plants from different CO[subscript 2], nitrogen and nodulation treatment conditions, highlights the fact that plants of same PI value are at the same developmental state, irrespective of the growth condition. Furthermore, changes in plant structure and function observed under different growth conditions can be related simply to changes in plastochron index. The work presented in this thesis demonstrate that changes in plant structure and function analyzed are related to changes in PI. An important finding of this thesis is that with the use of PI, results can be compiled as a template for predicting the structure- function state of pea plants at any plastochron age, under any growth conditions, before using small representative sample populations.

Brassinosteroids (BRs) have long been known to be effective in plant growth promotion. However, definitive evidence of BR's role in growth stimulation has remained unclear. Recently, genetic approaches using BR-deficient dwarf(dwf) mutants have begun to unravel the role of BRs in plant growth and development. BR dwarf mutants are characterized by multiple growth alterations: robust stem, reduced fertility, prolonged life cycle, dark-green appearance, round and curled leaves, and when grown in the dark, short hypocotyls and expanded cotyledons. Genetic analysis of the dwf mutants defined eight independent genetic loci defective in BR biosynthesis or perception. Allelism tests with previously reported genes revealed that d̲i̲m̲inuto 1 (dim1) was an allele of dwf1, and dwf2, dwf3, and dwf6 are allelic to b̲r̲assinosteroid i̲nsensitive (bri), c̲onstitutive p̲hotomorphogenesis and d̲warfism (cpd), and d̲e̲-e̲t̲iolated2 (det2), respectively. dwf4, dwf5, dwf7, and dwf8 were found to be novel and are the focus of this research. Anatomical analysis demonstrates that a reduction in cell length causes dwarf phenotype. Dwarfism was rescued by exogenous application of BRs. Feeding studies utilizing BR biosynthetic intermediates were employed to identify defective steps of BR biosynthesis in each of these dwarf mutants. dwf4 mutants were rescued only by 22α hydroxylated BRs, suggesting that the 22α hydroxylation reactions, putative rate-determining steps, are blocked. In fact, DWF4 has been cloned and shown to encode a cytochrome P450 steroid hydroxylase. Feeding studies also showed that dwf8 plants are rescued only by intermediates after 3 dehydrogenation reactions, indicating that the 3-dehydrogenase is defective in dwf8 plants. Gas Chromatography-Selective Ion Monitoring (GC-SIM) analysis of endogenous BRs in dwf5 plants showed that the level of 24-methylene cholesterol is greatly diminished as compared to wild type, suggesting that the biochemical defect occurs before 24-methylene cholesterol. Similar to dwf5, the biosynthetic defect in dwf7 is also shown to be in a step before 24-methylene cholesterol. The pleiotropic phenotypes in these dwf mutants due to biochemical defects in BR biosynthesis suggests that BRs are essential for proper growth and development of plants.

Carotenoids are C₄₀ tetraterpenoids synthesized by nuclear-encoded, multi-enzyme complexes located in the plastids of higher plants. In order to further understand the components and mechanisms involved in carotenoid biosynthesis, our laboratory has identified Arabidopsis thaliana mutants that disrupt this pathway. Here, I report the identification and characterization of three non-allelic albino mutations, pds1, pds2, and pds3 (pds = b phytoene desaturation), that are disrupted in phytoene desaturation, an early step in carotenoid biosynthesis. pds1 and pds2 have been more thoroughly characterized than pds3. Surprisingly, neither pds1 nor pds2 maps to the locus encoding the phytoene desaturase enzyme, indicating the products of at least three loci are required for phytoene desaturation. Electron transport chain components are hypothesized to be involved in phytoene desaturation and the analysis of pds1 and pds2 provide the first genetic evidence that plastoquinone is an essential component in carotenoid biosynthesis. Both mutants are plastoquinone and tocopherol deficient, in addition to their inability to desaturate phytoene, affecting distinct steps of the common plastoquinone/tocopherol biosynthetic pathway. The pds1 mutation affects the enzyme p-hydroxyphenylpyruvate dioxygenase (HPPD) as it can be rescued by growth on the product but not the substrate of this enzyme, homogentisic acid and p-hydroxyphenylpyruvate, respectively. The pds2 mutation most likely affects the prenyl/phytyl transferase enzyme of this pathway. Additionally, I report the isolation of an Arabidopsis HPPD cDNA, the first from a higher plant, which encodes a 50 kD polypeptide with between 29 and 40% identity to non-plant HPPDs. Alignment of the Arabidopsis HPPD with non-plant HPPDs identifies 38 identical amino acid residues, including six tyrosine and histidine residues thought to form the ferric iron center of the enzyme. When expressed in E. coli, the Arabidopsis HPPD catalyzes the accumulation of two compounds, homogentisic acid and ochronotic pigment, a polymerized oxidation product of homogentisic acid. Additionally, the Arabidopsis HPPD locus and the pds1 locus co-segregate. Finally, and most-significantly, the constitutive expression of the Arabidopsis HPPD cDNA in the pds1 mutant background complements the pds1 mutant. Taken together, these data suggest that pds1 is a mutation in the HPPD gene.

Growth, productivity and fruit quality of grapevines are closely linked to soil water availability. Withholding of water for any length of time results in slowed growth. If drought continues yield may be lost. Vines can be manipulated to stimulate early defence mechanisms by decreasing soil water availability. By using an irrigation technique, which allows for separate zones with different soil moisture status, it is possible to stimulate response mechanisms of the root system which are normally related to water stress. The difficulty of separating 'wet' and 'dry' zones was initially overcome by using split-root plants with root systems divided between two containers. Such experiments on split-root model plants resulted in the development of an irrigation technique termed partial rootzone drying (PRD). Results from irrigation experiments using PRD have shown that changes in stomatal conductance and shoot growth are some of the major components affected (Dry et al., 1996). The idea of using irrigation as a tool to manipulate stress responses in this way had its origin in the concept that root- derived abscisic acid (ABA) was important in determining stomatal conductance (Loveys, 1984). Later experiments on split-root plants have demonstrated that many effects of water stress can be explained in terms of transport of chemical signals from roots to shoots without changes in plant water status (Gowing et al., 1990). The necessary chemical signals are provided by the dry roots, and the wet roots prevent the development of deleterious water deficits. The general hypothesis tested during this study was that partial drying of the root system gives rise to a change in the supply of root-derived chemical signals which determine changes in grapevine physiology, thereby affecting fruit quality. Experiments were conducted on split-root vines (Vitis vinifera L. cvs. Cabernet Sauvignon and Chardonnay) grown in pots of different sizes, on field-grown vines which had either their root system divided by a plastic membrane (Vitis vinifera L. cv. Cabernet Sauvignon on own roots or grafted on Ramsey rootstocks) or conventional vines with a non-divided root system (Vitis vinifera L. cv. Cabernet Sauvignon, Shiraz and Riesling) with a commercial PRD irrigation design. The irrigation treatments were vines receiving water on both sides (control) and PRD-treated vines, which only received water on one side at any time. The frequency of alternation of 'wet' and 'dry' sides was determined according to soil moisture and other influences such as rainfall and temperature. In most of the experiments the irrigation was alternated from one side to the other every 10 to 15 days. Chemical signals from roots: the role of ABA and cytokinins Studies on chemical signals have concentrated on ABA and cytokinins (CK). An improved stable isotope dilution protocol, which enables analysis of ABA and CK from the same tissue sample, was developed. Analysis of cytokinins focused on zeatin (Z), zeatin riboside (ZR), zeatin glucoside (ZG) and iso pentenyl adenine (iP). Roots are relatively inaccessible, particularly in field situations. To enable easier access to roots of field-grown vines, split-root vines were planted in a trench which was refilled with a sandy soil. This created a homogenous soil substrate and did not restrict root growth while still allowing access to roots under field conditions. Analyses of root samples of field-grown vines have shown that cytokinins and ABA may originate in roots and their concentrations can be substantially altered during an irrigation cycle. Alternating soil water conditions showed that [ABA] in roots on the 'dry' side was significantly higher compared with the 'wet' side. Due to a reduction in CK on the 'dry' side of PRD-treated vines, the ratio between ABA and CK was substantially changed during an irrigation cycle. The ABA levels in root tissue and in petiole xylem sap were negatively related to stomatal conductance. This further suggests that ABA, mostly synthesized on the 'dry' side of the root system, might be responsible for a decline in stomatal conductance. Furthermore, a higher pH of petiole xylem sap was observed in PRD-treated vines which may also contribute to the regulation of stomatal conductance. Studies on stomatal patchiness showed that non-uniform stomatal aperture occurred in field-grown vines under natural environmental conditions and was more abundant under PRD conditions. The degree of stomatal opening, determined by using a water infiltration technique, correlated with measurement of stomatal conductance. Exogenous application of a synthetic cytokinin (benzyl adenine) can override the possible ABA-mediated stomatal closure resulting from PRD treatment, providing further evidence for the in vivo role of these growth regulators in the control of stomatal conductance. The effect of benzyl adenine was transient, however, requiring repeated applications to sustain the reversal. In addition, CKs may also be important in influencing grapevine growth. Following several weeks of repeated spray applications with benzyl adenine, it was found that the development of lateral shoots in PRD-treated vines was enhanced compared to PRD-treated vines sprayed with water only. This supports the idea that the reduction in lateral shoot development seen in PRD-treated vines is due to a reduced production of CKs (Dry et al., 2000a). By measuring shoot growth rate it was found that one common feature of PRD-treated vines, which were not sprayed with CK, was a reduction of lateral shoot growth. It can therefore be speculated that the reduction in lateral growth is related to a reduced delivery of cytokinins from the roots. Zeatin and zeatin riboside concentration in shoot tips and prompt buds/young lateral shoots were reduced by the PRD treatment providing further evidence in support of this hypothesis. Water movement from 'wet' to 'dry' roots Roots, being a primary sensor of soil drying, play an important role in long- and short-term responses to PRD. Using stable isotopes of water and heat-pulse sap flow sensors water movement was traced from wet to dry roots in response to PRD. The redistribution of water from roots grown in a soil of high water potential to roots growing in a soil of low water potential may be of significance with regard to the movement of chemical signals and the control of water balance of roots. Measurements of the relative water content (RWC) have shown a slower decline of RWC of the 'dry' roots of PRD vines relative to roots of vines which received no water, despite similar water content in soil surrounding those roots. The redistribution of water may help to sustain the response to PRD for longer periods possibly releasing chemical signals and to support the activity of fine roots in drying soil. Field vines, irrigated with PRD over several growing seasons, altered their root distribution relative to the control vines. PRD caused a greater concentration of fine roots to grow in deeper soil layers and this may contribute to a better water stress avoidance. The effect on root growth may be augmented by the water movement and by the large difference in ABA to cytokinin ratio, which are also known to alter root growth. PRD makes more efficient use of available water In experiments where both control and PRD-treated vines received the same amount of water many differences between the vines were demonstrated. Under conditions where water supply was adequate for both treatments, the stomatal conductance and growth of the PRD-treated vines was restricted as has been observed in many previous experiments. As total water input was reduced, however, the stomatal conductance of PRD-treated vines became greater than control vines, suggesting that the latter were experiencing a degree of water stress, whereas the PRD-treated vines were not. This may have been due to the greater depth of water penetration in the case of the PRD-treated vines, where water was applied to a smaller soil surface area. This distinction between PRD-treated and control vines, at very low water application rates, was also reflected in pruning weights and crop yields which were actually greater in PRD-treated vines. It was concluded that at low water application rates, the PRD-treated vines were more tolerant of water stress and made more efficient use of available water. Reduction in vigor opens the canopy. The initial aim of the research which led to the development of PRD was to achieve better control of undesirable, excessive shoot and foliage growth which, from a viticultural point of view, has many disadvantages. Grapevine shoot growth rate responds very sensitively to drying soil conditions. The irrigation strategy used in the PRD experiments maintained a reduction of both main shoot and lateral shoot growth. In response to PRD a decrease in shoot growth rate and leaf area was observed. Much of the reduction in canopy biomass was due to a reduced leaf area associated with lateral shoots, thus influencing the canopy structure. This was one major factor improving the light penetration inside the canopy. Control of vegetative vigour results in a better exposure of the bunch zone to light and, as a consequence, in improved grape quality. It is likely that changes in canopy density, as a result of PRD, is causing changes in fruit quality components. Anthocyanin pigments such as derivatives of delphinidin, cyanidin, petunidin and peonidin were more abundant in berries from PRD vines; by comparison the concentration of the major anthocyanin, malvidin, was reduced. When leaves were deliberately removed from more vigorous control vines, which improved bunch exposure, the differences in fruit composition were much reduced. This further supports the idea that a more open canopy, in response to PRD, improves fruit quality by affecting the canopy structure. Fruit quality consequently determines the quality, style and value of the finished wine. Wines from this study have been produced and data on wine quality from commercial wineries are also available. Sensory evaluations have demonstrated that high wine quality from PRD-treated vineyards can be achieved without any yield-depressing effects. This study has provided evidence to support the original hypothesis. The major findings were: a) Chemical signals, altered under PRD and mostly originating from roots, play an important role in the root to shoot communication in grapevines. b) The movement of water from 'wet' to 'dry' soil layers may help to sustain chemical signals as a response of grapevines to PRD and to support the activity of fine roots in drying soil. c) A reduction in vegetative growth, in particular of lateral shoots, was sustained using PRD and affected the canopy structure which in turn, due to a better light penetration into the canopy, improved the fruit quality. d) The reduction in irrigation water applied did not have a detrimental effect on grape yield and thus the efficiency of water use was improved. e) Application of relatively low irrigation rates showed that PRD-treated vines were more tolerant of water stress and made more efficient use of available water.
Thesis (Ph.D.)--Department of Horticulture, Viticulture and Oenology, 2000.

Jasmonates (JAs) play a major role in plant defense against herbivores while some caterpillar species use effectors in their labial saliva to suppress the induction of JA-mediated defense responses. On the other hand, activation of plant defense is associated with slowed plant growth which is controlled by gibberellins (GA) and growth repressor DELLA proteins. Recent studies have shown that DELLA proteins play an important role in plant stress response and are involved in the crosstalk between JA and GA pathways. However, the role of DELLA proteins in plant-insect interactions remains unclear. In this study, wild-type Arabidopsis, wild-type sprayed with GA and a quadruple-della Arabidopsis mutant (quad-della) were subject to herbivory by beet armyworm Spodoptera exigua caterpillars with either intact or impaired labial salivary secretions. Wild-type Arabidopsis, Arabidopsis + GA and the quad-della mutant showed a JA burst in response to herbivory. This was reflected in increased transcript levels of the JA-dependent gene markers, such as AtPDF1.2, AtLOX2 and AtVSP2. A caterpillar saliva-specific pattern of JA hormone levels (JA, JA-isoleucine, OPDA) were observed in the wild-type background but not in the quad-della mutant, suggesting that DELLAs are involved in plant response to caterpillar saliva, probably by mediating the crosstalk between JA- and salicylic acid (SA)-dependent pathways. Additionally, high constitutive expression of the SA pathway marker gene AtPR1 was observed in the quad-della mutant but not in wild-type Arabidopsis, which indicates that DELLAs play a role in maintaining the homeostasis of SA signalling by repressing its constitutive induction.
Les Jasmonates (JAs) font une partie importante dans la défense des plantes contre les herbivores. Certaines espèces de chenilles utilisent des effecteurs dans leur salive labiale pour supprimer l'induction de réponses de défense induites par les JAs. En revanche, l'activation de défense de la plante est associée au ralentissement de la croissance des plantes. La croissance des plantes est contrôlée par les gibbérellines (GA) et les répresseurs de la croissance, les protéines DELLA. Des études récentes ont montré que les protéines DELLA font partie de la réponse des plantes au stress et participent à la diaphonie entre les voies métaboliques du JA et GA. Cependant, le rôle des protéines DELLA reste incertain. Dans cette étude, Arabidopsis type sauvage, Arabidopsis type sauvage traités avec une pulvérisation du GA, et le mutant quadruple-della (quad-della) souffert des attaques par le herbivore Spodoptera exigua. Les chenilles sont normales ou avec les facultés affaiblies dans les glandes salivaires. Les trois groupes des plantes ont montré une explosion du JA en réponse aux herbivores. Cette réponse a été reflétée dans les niveaux de transcription des gènes dépendant de JA, comme AtPDF1.2, AtLOX2 et AtVSP2. Un motif spécifique à la salive des niveaux des hormones JA (JA, JA-isoleucine, OPDA) a été observé dans le type sauvage mais pas dans les mutants. Ce résultat suggère que DELLAs sont impliquées dans la réponse de la plante à la salive probablement par la médiation de la diaphonie entre les voies métaboliques du JA et du acide salicylique (SA). Ailleurs, une forte expression du gène AtPR1, qui est partie de la voie d'SA, a été observé dans le mutant quad-della. Ce résultat suggère que DELLAs sont impliquées dans l'homéostasie de la signalisation de SA en réprimant son expression constitutive.

Thesis (Ph.D.) -- University of Western Sydney, Hawkesbury, 1999.
Thesis submitted for the degree of Doctor of Philosophy. Spine title: Towards an understanding of vitrification in tissue cultured plants. Includes bibliographical references (leaves 175-203).

Thesis (MTech (Agriculture)--Cape Peninsula University of Technology, 2018.
Choumollier (narrow-stem kale) (Brassica oleracea, L.) has been progressively used in recent years as a supplementary forage harvest in many countries with a temperate climate. Boron (B) and calcium (Ca) are the two most important elements for supporting plant structure and function of plasma membranes. Boron nutrition is vital for obtaining high quality yields in vegetables. The main objective of this study was to evaluate the extent to which boric acid concentration can affect growth parameters (plant height, leaf numbers, chlorophyll levels, and leaf size) of Brassica olereacea var. acephala at different stages of growth and development. Treatment comprised of four concentrations of boron (0.3 mg/kg, 0.4 mg/kg, 0.5 mg/kg and 0.6 mg/kg). Yield and physiological growth responses were measured during the course of the study to ascertain effectiveness and influence of boron treatments on the test crops. Leaves of B. oleracea were harvested at weekly intervals (W1, W2, W3, W4 and W5) after each treatment regimen for approximate basic mineral analysis and composition. Soil pH did not vary much among the various orchard blocks tested, regardless of soil depth. Exchangeable cations Na+ and K+ levels did not vary significantly, but Ca2+ and Mg2+ levels fluctuated considerably among orchards analyzed. The Control Orchard exhibited a higher P content than the other orchards. Ca, Mg, Cu and B levels did not vary significantly among the orchards, but Na, Fe and Zn levels were markedly raised in the Orchard treated with 0.3 mg/kg boron) relative to the Control Orchard. Chlorophyll fluorescence was significantly dependent on the treatment dose of boron as compared to control. Chlorophyll fluorescence also increased significantly with the growth period, i.e., the duration following the initial treatment at all doses of boron. Boron at all did not significantly affect leaf count, leaf length and plant height. The work may add to the body of knowledge on the influence of boron on the physiological performance, mineral contents and proximate composition of leaves of the species. Furthermore, the findings may have important applications in achieving high quality yields in vegetable crops.

Cyanobacteria are an ancient and globally distributed group of photosynthetic prokaryotes including species capable of fixing atmospheric dinitrogen (N2) into biologically available ammonia via the enzyme complex nitrogenase. The ability to form symbiotic interactions with eukaryotic hosts is a notable feature of cyanobacteria and one which, via an ancient endosymbiotic event, led to the evolution of chloroplasts and eventually to the plant dominated biosphere of the globe. Some cyanobacteria are still symbiotically competent and form symbiotic associations with eukaryotes ranging from unicellular organisms to complex plants. Among contemporary plant-cyanobacteria associations, the symbiosis formed between the small fast-growing aquatic fern Azolla and its cyanobacterial symbiont (cyanobiont), harboured in specialized cavities in each Azolla leaf, is the only one which is perpetual and in which the cyanobiont has lost its free-living capacity, suggesting a long-lasting co-evolution between the two partners. In this study, the genome of the cyanobiont in Azolla filiculoides was sequenced to completion and analysed. The results revealed that the genome is in an eroding state, evidenced by a high proportion of pseudogenes and transposable elements. Loss of function was most predominant in genetic categories related to uptake and metabolism of nutrients, response to environmental stimuli and in the DNA maintenance machinery. Conversely, function was retained in key symbiotic processes such as nitrogen-fixation and cell differentiation. A comparative analysis shows that the size of the cyanobiont genome has remained relatively stable, and that few genes have been completely eliminated, since the symbiotic establishment. Indications of genes acquired via horizontal gene transfer were discovered in thec yanobiont genome, some of which may have originated from the bacterial community in the Azolla leaf-cavities. It is concluded that the perpetual nature of the Azolla symbiosis has resulted in pronounced ongoing streamlining of the cyanobiont genome around core symbiotic functions, a process not described previously for complex cyanobacteria or for any bacterial plant symbiont. Further, the status of the genome indicates that the cyanobiont is at an early stage of adapting to its host-restricted environment and continued co-evolution with the plant may result in additional genome reductions. However, although a vertical transmission process is already established, the unusual extracellular location of the cyanobiont and the intricate nature of the symbiosis, may still impose restrictions on such a reductive process.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript.

As the demand for energy rises, Populus species are increasingly grown as bioenergy crops. Meanwhile, due to global change, predictions indicate that summer droughts will increase in frequency and intensity over Europe. This study was carried out to evaluate the adaptation to drought in Populus, at different levels: genetic, genomics and physiology. Forests trees such as poplar are very important ecologically and economically but the Populus genus is known to be drought sensitive. Consequently, it is essential to understand drought response and tolerance for those trees. Two populations of poplar were used for this study, a mapping population (Family 331) and a natural population of Populus nigra. The F2 mapping population obtained from a cross of Populus deltoides and Populus trichocarpa, showed differences in stomatal conductance and carbon isotope composition in both clones and the F2 progeny. It was also used to discover QTL related to water use efficiency highlighting interesting areas of the genome. Combining QTL discovery and microarray analysis of the two clones in response to drought, a list of candidate genes was defined for water use efficiency. The natural population of Populus nigra consisting of 500 genotypes of wild black poplar showed variation in numerous physiological measurements such as leaf development and carbon isotope discrimination in well-watered conditions depending on their latitude of origin. The drier genotypes (from Spain and South France) had the smallest leaf area which could be linked to an adaptation to drought. Physiological measurements of extreme genotypes in leaf size of this population revealed differences in response to water depending on their latitude of origin. Stomatal conductance rapidly decreased and water use efficiency improved for Spanish genotypes after a slow and moderate drought stress. Direct comparisons between the transcriptome of extreme genotypes from Spain and North Italy in well watered and drought conditions provided an insight into the genomic pathways induced during water deficit. Six candidate genes were selecting for further analysis using real-time PCR: two stomatal development genes (ERECTA and SPEECHLESS), two ABA related genes (ATHVA22A and CCD1), a second messenger (IP3) and a NAC transcription factor (RD26)

Master of Science
Department of Biology
Jesse B. Nippert
In 1902, President Theodore Roosevelt signed and enacted the Reclamation Act, which would fundamentally alter the lowland hydrology of the arid southwest over the next century. Flow regulations, groundwater pumping, damming, and river channel changes have led to decreases in water table heights and periodic overbank flooding, and subsequently, increased soil salinity in the arid Southwest. During this period, native riparian tree species have declined significantly and an invasive tree species, Tamarix ramosissima, has increased in abundance and distribution. Increases in soil salinity negatively impact the physiology of native riparian tree species, but the impacts of soil salinity on Tamarix physiology are incompletely known. I studied the impact of increasing soil salinities on the physiology of Tamarix in both field and controlled environments. I first studied the impacts of increasing soil salinities on Tamarix physiology at two semi-arid sites in western Kansas. I concluded that physiological functioning in Tamarix was maintained across a soil salinity gradient from 0 to 14,000 ppm illustrating robust physiological responses. Using cuttings from Tamarix trees at both sites, I subjected plants to higher NaCl concentrations (15,000 and 40,000 ppm). Tamarix physiology was decreased at 15,000 ppm and 40,000 ppm. Tamarix physiological functioning was affected at the induction of treatments, but acclimated over 30-40 days. These results reveal a threshold salinity concentration at which Tamarix physiological functioning decreases, but also illustrate the advantageous halophytic nature of Tamarix in these saline environments. Many arid and semi-arid environments are predicted to become more saline, however, results from both studies suggest that increasing salinity will not be a major barrier for Tamarix persistence and range expansion in these environments.

Biophysical models were developed for biomass accumulation, transpiration and carbon dioxide (CO₂) assimilation of Agave pacifica as functions of air CO₂ concentration, photosynthetic photon flux (PPF) and irrigation interval. Parameter estimation and validation were performed for the Gompertz's equation for biomass accumulation and for the Penman-Monteith equation for transpiration. A new biophysical model for CO₂ assimilation is proposed consisting of four components: stomatal opening and CO₂ fixation; malic acid accumulation; malic acid depletion; and photosynthetic carbon assimilation. The main and interactive effects of air CO₂ concentration, PPF and irrigation interval on biomass accumulation, transpiration and CO₂ assimilation of Agave pacifica were also determined.

The principal aim of the research presented in this thesis was to investigate factors affecting the "male competition" component of sexual selection in the hermaphroditic species, Senecio vulgaris. As male reproductive function consists of attracting pollinators and the success of pollen in contributing genes to the next generation, sexual selection will act on both the sporophytic and gametophytic stages of the life cycle. The potential for, and consequences of male competition were analysed at both pre- and post-pollination stages. A comparison of the relative attractiveness of the radiate and non-radiate morphs of S.vulgaris to pollinators revealed that in mixed stands, pollinators discriminated in favour of the radiate morph irrespective of the frequency of the two morphs in a population. Measurement of intramorph and intermorph maternal outcrossing rates showed the radiate morph always outcrossed at higher levels than the non-radiate morph. Both morphs exhibited levels of male outcrossing, the radiate morph exhibited higher levels of intramorph paternal outcrossing while non-radiate pollen was more successful than radiate pollen in intermorph crosses. The potential levels of intermorph and intramorph pollen competition experienced by the radiate and non-radiate pollen types suggest radiate pollen was subjected to greater levels of competition for access to ovules than non-radiate pollen. Examination of post-pollination events suggested that radiate pollen germinates faster than non-radiate pollen when applied to stigmas of either morph. However, no consistent evidence of radiate pollen tubes outcompeting non-radiate pollen tubes in the style and consequently fertilising a disproportionate share of available ovules was obtained. The problems associated with measuring pollen competitive ability are discussed. In addition to the research on male competition, a study was also conducted to examine the origin of the radiate morph of S.vulgaris. Morphometric and electrophoretic analyses provided strong evidence that a radiate variant from York possessed more 'squalidus-like' characters than are generally found in radiate S.vulgaris. It is suggested that this radiate form may represent an early stage in the origin of radiate S.vulgaris via introgression of S.squalidus into S.vulgaris.

Waste products from the forest industry are to be spread in forests in Sweden to counteract nutrient depletion due to whole tree harvesting. This may increase the bioavailability of calcium (Ca) and heavy metals, such as cadmium (Cd), copper (Cu) and zinc (Zn) in forest soils. Heavy metals, like Cd, have already been enriched in forest soils in Sweden, due to deposition of air pollutions, and acidification of forest soils has increased the bioavailability of toxic metals for plant uptake. Changes in the bioavailability of metals may be reflected in altered accumulation of Ca and heavy metals in forest trees, changes in tree growth, including wood formation, and altered tree species composition. This thesis aims at examining: A) if inter- or intra- specific differences in sensitivity to Cd occur in the most common tree species of Sweden, and if so, to study if these can be explained by the uptake and distribution of Cd within the plant: B) how elevated levels of Ca, Cd, Cu and Zn affect the accumulation and attachment of metals in bark and wood, and growth of young Norway spruce (Picea abies): C) how waste products from the forest industry, such as wood ash, influence the contents of Ca, Cd, Cu and Zn in wood and bark of young Norway spruce.

Sensitivity to Cd, and its uptake and distribution, in seedlings of Picea abies, Pinus sylvestris and Betula pendula from three regions (southern, central and northern parts) of Sweden, treated with varying concentrations of Cd, were compared. Differences in root sensitivity to Cd both among and within woody species were found and the differences could to some extent be explained by differences in uptake and translocation of Cd. The root sensitivity assays revealed that birch was the least, and spruce the most, sensitive species, both to the external and to tissue levels of Cd. The central ecotype of the species tested tended to be most Cd resistant.

The radial distribution, accumulation and attachment of, and interactions between Ca and heavy metals in stems of two-year-old Norway spruce trees treated with elevated levels of Cd, Cu, Zn and/or Ca, were investigated. Further, the influence of these metals on growth, and on root metal content, was examined. Accumulation of the metals was enhanced in wood, bark and/or roots at elevated levels of the metal in question. Even at low levels of the metals, similar to after application of wood ash, an enhanced accumulation was apparent in wood and/or bark, except for Cd. The increased accumulation of Zn and Cu in the stem did not affect the growth. However, Cu decreased the accumulation of Ca in wood. Higher levels of Cu and Cd reduced the stem diameter and the toxic effect was associated with a reduced Ca content in wood. Copper and Cd also decreased the accumulation of Zn in the stem. On the other hand, elevated levels of Ca increased the stem diameter and reduced the accumulation of Cd, Cu, Zn and Mn in wood and/or bark. When metals interacted with each other the firmly bound fraction of the metal reduced was in almost all cases not affected. As an exception, Cd decreased the firmly bound fraction of Zn in the stem.

The influence of pellets of wood ash (ash) or a mixture of wood ash and green liquor dregs (ash+GLD), in the amount of 3000 kg ha^-1, on the contents of Ca, Cd, Cu and Zn in wood and bark of young Norway spruce in the field was examined. The effect of the treatments on the metal content of bark and wood was larger after 3 years than after 6 years. Treatment with ash+GLD had less effect on the heavy metal content of bark and wood than treatment with ash alone. The ash treatment increased the Cu and Zn content in bark and wood, respectively, after 3 years, and decreased the Ca content of the wood after 6 years. The ash+GLD treatment increased the Ca content of the bark and decreased the Zn content of bark and wood after 3 years. Both treatments reduced, or tended to decrease, the Cd content in wood and bark at both times.

To conclude, small changes in the bioavailability of Ca, Cu, Cd and Zn in forest soils, such as after spreading pellets of wood ash or a mixture of wood ash and green liquor dregs from the forest industry, will be reflected in an altered accumulation of metals in wood and bark of Norway spruce. It will not only be reflected in changed accumulation of those metals in which bioavailability in the soil has been enhanced, but also of other metals, probably partly due to interactions between metals. When metals interact the exchangeable bound fraction of the metal reduced is suggested to be the main fraction affected. The small alterations in accumulation of metals should not affect the growth of Norway spruce, especially since the changes in accumulation of metals are low, and further since these decrease over time. However, as an exception, one positive and maybe persistent effect of the waste products is that these may decrease the accumulation of Cd in Norway spruce, which partly may be explained by competition with Ca for uptake, translocation and binding. A decreased accumulation of Cd in Norway spruce will probably affect the trees positively, since Norway spruce is one of the most sensitive species to Cd of the forest trees in Sweden. Thus, spreading of waste products from the forest industry may be a solution to decrease the accumulation of Cd in Norway spruce. In a longer perspective, this will decrease the risk of Cd altering the tree species composition of the forest ecosystem. An elevated bioavailability of Ca in forest soils will, in addition to Cd, probably also decrease the accumulation of other less competitive heavy metals, like Zn and Mn, in the stem.

This thesis concerns a general approach to the total synthesis of yuehchukene 2 and its analogues. Yuehchukene has a potent anti-implantation activity. It also lacks the estrogenic side effect of most compounds with similar biological activity. However, it is somewhat unstable and this could bring some problems when administered to humans. Development of a versatile synthesis of yuehchukene capable of producing a variety of analogous structures in order to fully exploit the pharmacological properties of this novel molecular system and/or to make a more stable product without losing its biological properties was the central objective of this project. Specifically, the total synthesis of yuehchukene 2 and its analogue 6a-ep/-yuehchukene 25 are described. After some preliminary studies, it was found that a kinetic carboxylation (lithium 2,6-di-tert-butyl-4-methylphenoxide, CO₂) of isophorone 26 followed by a reduction (NaBH₄) produced stereoselectively cis-hydroxyacid 46 in good yield. The latter was transformed into indoleacid 48 by dibenzoylation (PhCOCI, DMAP) and treatment with indolylmagnesium iodide. The key intermediate trans-ketone 60 was obtained by treatment of 48 with oxalyl chloride followed by indolylmagnesium iodide. Epimerization of 60 to the more stable cis-ketone 24 was accomplished quantitatively under basic conditions (MeONa/MeOH, reflux). Reduction (LiAlH₄) and dibenzoylation (PhCOCI, DMAP, Et₃N) of 24 furnished the benzoate 68 which was subjected to a nucleophilic substitution with indolylmagnesium iodide to give N-benzoylyuehchukene 69. The latter transformation also gave the interesting compound 75 which was submitted to an X-Ray diffraction analysis. The total synthesis of yuehchukene 2 was then achieved by methanolysis (NaOMe/MeOH) of 69. As far as the synthesis of 6a-epi-yuehchukene 25 is concerned, it was found that, after a thorough study, it was best to transform trans-ketone 60 into its SEM-derivative 85 (SEM-CI,NaH). The latter was reduced (DIBAL) and acetylated (Ac₂O, DMAP, Et₃N) to produce stereoselectively the acetate 87 which, by treatment with indolylmagnesium iodide, furnished SEM-trans-yuehchukene 88. The newly incorporated indole group bears a 1,3-diaxial-like interaction with the β-methyl group at C-7. Unlike 88, tosylacetate 82 gave the compound 84. Finally, the total synthesis of 6a-epi-yuehchukene was accomplished by deprotection of the indole system. Various compounds from this study are now under investigation at WHO and in Hong Kong but, unfortunately, biological results are unavailable at present. [Formula Omitted]
Science, Faculty of
Chemistry, Department of
Graduate

The use of neem products to control the European corn borer, Ostrinia nubilalis (Hubner), in sweet corn was investigated. Three years of field studies were conducted comparing various foliar-spray applications of a neem seed kernel extract (NSKE), azadirachtin (AZA, the active ingredient of neem extracts), and Ambush (a synthetic pyrethroid). The results included: (1) NSKE sprayed prior to artificial infestation of the corn plants provided excellent protection (comparable to Ambush) against borer damage and greatly reduced larval populations. (2) Neem extract formulations from Safer Ltd. were the most effective. (3) The rate of application or number of applications were not determining factors in altering the efficacy of neem products. (4) Exceptional weather conditions (high temperatures, dry conditions) may be detrimental to the efficacy of foliar applied neem products. (5) Some neem treatments were found to increase corn stalk breakage possibly by altering the behavior of the larvae. Laboratory evaluations using no-choice leaf-disk bioassays showed the antifeedant action of AZA and the negligible effect of PBO (piperonyl butoxide) and Citowett (used in field formulations) on the feeding behavior of 3rd instar larvae. Growth and development studies of O. nubilalis fed a diet containing 0, 1, 3, 10, 30, 100, and 1000 $\mu$g NSKE g$\sp{-1}$ diet were conducted. 10 $\mu$g NSKE g$\sp{-1}$ diet (50 ng AZA g$\sp{-1}$ diet) fed continuously to the larvae were larvicidal and concentrations as low as 3 $\mu$g NSKE g$\sp{-1}$ diet (16.6 ng AZA g$\sp{-1}$ diet) significantly reduced larval, pupal and adult weights, increased the larval and pupal periods, decreased adult emergence and caused wing deformities. AZA content of the extracts was found to be a critical factor in the IGR (insect growth regulator) effects of NSKE. (Abstract shortened by UMI.)

This study postulates that the symbiosis between red clover, Trifolium pratense L., and the arbuscular mycorrhizal (AM) fungus, Glomus intraradices Schenck & Smith, enhances secondary phenolic metabolism and nitrogen assimilation. To test this hypothesis, the four objectives set forth were to determine the impact of AM colonization and/or rhizobial inoculation in red clover on the: (1) growth parameters; (2) nitrogen assimilation, via the activity of glutamine synthetase (GS, E.C. 6.3.1.2), total N content and soluble protein concentration; (3) contents of isoflavonoids (e.g. genistein, daidzein, biochanin A, and formononetin); and (4) contents of these four isoflavonoids over time and with a hormonal factor, jasmonic acid (JA). To accomplish these objectives, four greenhouse experiments were performed. The overall results indicate that the colonized red clover plants, with 22% to 37% of AM root colonization, had enhanced shoot height as well as increased shoot and root dry masses. Co-inoculation with Rhizobium enhanced the growth parameters more than inoculation with either microsymbiont alone. The concentrations of micronutrients significantly increased in red clover with AM colonization and/or rhizobial inoculation, while the macronutrients did not vary to any great degree. (Abstract shortened by UMI.)

In the present work the regulation of environmentally induced cell death and signaling of systemic acquired acclimation (SAA) in Arabidopsis thaliana is characterized. We used the lesion simulating disease1 (lsd1) mutant as a model system that is deregulated in light acclimation and programmed cell death (PCD). In this system we identify that redox status controlling SAA and cell death is controlled by the genes LSD1, EDS1, EIN2 and PAD4 which regulate cellular homeostasis of salicylic acid (SA), ethylene (ET), auxin (IAA) and reactive oxygen species (ROS). Furthermore we propose that the roles of LSD1 in light acclimation and in biotic stress are functionally linked. The influence of SA on plant growth, short-term acclimation to high light (HL), and on the redox homeostasis of Arabidopsis leaves was also assessed. SA impaired acclimation of wild-type plants to prolonged conditions of excess excitation energy (EEE). This indicates an essential role of SA in acclimation and regulation of cellular redox homeostasis. We also show that cell death in response to EEE is controlled by specific redox changes of photosynthetic electron transport carriers that normally regulate EEE acclimation. These redox changes cause production of ET that signals through the EIN2 gene and regulon. In the lsd1 mutant, we found that propagation of cell death depends on the plant defence regulators EDS1 and PAD4 operating upstream of ET production. We conclude that the balanced activities of LSD1, EDS1, PAD4 and EIN2 regulate chloroplast dependent acclimatory and defence responses. Furthermore, we show that Arabidopsis hypocotyls form lysigenous aerenchyma in response to hypoxia and that this process involves H2O2 and ET signalling. We found that formation of lysigenous aerenchyma depends on LSD1, EDS1 and PAD4. Conclusively we show that LSD1, EDS1 and PAD4, in their functions as major plant redox and hormone regulators provide a basis for fundamental plant survival in natural contitions.

ABSTRACT Bacteriocins are small peptides, produced by many bacteria, which have adverse effects on microorganisms closely related to the producer strain. Two new Class IId bacteriocins, thuricin 17 and bacthuriocin F4 were isolated from plant growth promoting rhizobia (PGPR). Initial studies showed that both the bacteriocins can promote soybean growth. My experimental results demonstrated that these two bacteriocins promoted germination and emergence of corn, soybean, canola and wheat, but had no effect on barley, when compared with the control under optimal growth conditions. Of the tested crops, corn was most positively affected. Further abiotic stress experiments on corn showed that the two bacteriocins promoted corn emergence under low temperature, high salinity and polyethylene glycol induced water deficit stress. Field experiment data also showed that thuricin 17 can effectively promote corn emergence under cool spring field conditions in southwestern Quebec.
RÉSUMÉ Les bacteriocines sont les petits peptides produits par les bactéries qui ont des effets défavorables sur les microorganismes génétiquement proches de la souche productrice. Deux nouvelles bacteriocines de la classe IId, thuricin 17 et bacthuriocin F4, ont été isolées de bactéries présentes dans la rhizosphere et qui promouvoit la croissance des plantes (PGPR). Des études préalables ont démontré que ces deux bacteriocines peuvent promouvoir la croissance du soja. Mes résultats expérimentaux ont démontré que ces deux bacteriocines promouvoit la germination et l'émergence du maïs, du soja, du canola et du blé, mais n'ont pas d'effet sur l'orge, lorsque comparées aux contrôles sous des conditions optimales pour la croissance. Parmi les cultures testées, le maïs était le plus positivement affecté. Les expériences subséquentes sous stress abiotiques ont démontré que les deux bacteriocines ont augmenté l'émergence du maïs sous conditions de basse température, de salinité et de stress hydrique provoqué par le glycol de polyéthylène. Aussi, les expérimentations en champ ont démontré que le thuricin 17 peut promouvoir efficacement l'émergence du maïs dans le sud-ouest du Québec, où les températures printanières sont souvent fraîches.

This thesis involved an investigation of potato (Solanum tuberosum L.) tuber antioxidant capacity, particularly the phytonutrients vitamin C and polyphenolics. Tubers of 12 Canadian-grown and 5 foreign cultivars were screened for antioxidants qualitatively and quantitatively following 1 and 7 months of storage (5±1 oC). Significant differences were seen in quality and quantity of tuber antioxidants (including vitamin C and polyphenolics) between cultivars, storage intervals, and tuber tissues (skin, cortex, and pith). A potato microtuber model system was developed to test the effects of hormesis on microtuber antioxidant capacity. Hydrogen peroxide sprays (2 and 4 mM) increased the antioxidant capacity of microtubers in 2 cultivars by 12-26 %, showing the potato microtuber model system to be sensitive and useful for manipulating phytonutrient composition via hormetic treatments. Information in this thesis may have future applications for better cultivar selection and cultivation practices for improved phytonutrient content of field-grown potato tubers.
La capacité antioxydante des tubercules de pomme de terre (Solanum tuberosum L.), particulièrement celle conférée par la vitamine C et les polyphénoliques, fit l'objet de cette étude. La teneur et la gamme des antioxydants présents dans les tubercules de 12 cultivars de pomme de terre sélectionnés au Canadiens et 5 cultivars sélectionnés à l'étranger, ont été.evalués après 1 ou 7 mois d'entreposage à 5±1oC. Le cultivar, la durée d'entreposage, et le tissu échantillonné (peau, chair, ou moelle) eurent tous un effet significatif sur la teneur et la gamme des antioxydants (vitamine C et les polyphénoliques) présents. Un système modèle avec microtubercules servit à l'examen d'effets d'hormèse sur la teneur en antioxydants des microtubercules de deux cultivars. Une aspersion au péroxide (2 ou 4 mM) augmenta de 12% à 26% la capacité antioxydante de microtubercules de deux cultivars différents, indiquant que ce système modèle est sensible et se prête bien à la manipulation du contenu nutritif des tubercules par traitements hormetiques. Ces connaissances pourraient s'avérer utile dans la sélection de cultivars et la mise en oeuvre de pratiques culturales pouvant améliorer, au champ, le contenu nutritif des pommes de terre.

Long exposure to low non-freezing temperatures accelerates flowering and triggers cold acclimation in winter wheat and barley. Cold tolerance is a complex but important trait that influences yield considerably. Brachypodium distachyon is an annual temperate wild grass species and is a powerful model to study grass biology, but the capacity of this plant to tolerate freezing is unknown. An integrated approach involving double ridge formation, final leaf number, and osmoprotectant content was used to confirm the growth habit and freezing tolerance ability of seven diploid Brachypodium distachyon accessions. In addition, expression analyses of orthologs of the major vernalization regulator VRN1 and COR genes including an antifreeze protein and a temperature-induced lipocalin (TIL) were conducted. Our results demonstrate that formerly classified spring accessions behaved more like facultative accessions by showing increased osmoprotectants and COR transcripts accumulation upon cold exposure. The confirmed winter accessions acquired vernalization saturation after 49 days and accumulated COR transcripts to higher levels although no significant difference was observed between the osmoprotectant content of spring and winter accessions. Transgenic lines overexpressing a TIL were also generated to increase the freezing tolerance capacity of the spring accession Bd21. This study validates Brachypodium distachyon as a valuable model system to study freezing tolerance in temperate cereals.
Les basses températures au-dessus de zéro accélèrent la floraison et déclenchent l'acclimatation au froid chez le blé et l'orge d'hiver. La tolérance au gel est un trait complexe et important qui influence les rendements considérablement. Brachypodium distachyon (Brachypodium) est une céréale annuelle de climat tempéré et un puissant modèle pour étudier la biologie des monocotylédones, mais les capacités de tolérance au gel de cette plante sont inconnues. Une approche intégrée impliquant la formation de la ride double, le nombre de feuilles final et la concentration d'osmoprotectants a été utilisée afin de confirmer l'habitude de croissance (de printemps ou d'hiver) et les capacités de tolérance au gel de sept cultivars diploïdes de Brachypodium. En parallèle, nous avons analysé l'expression des orthologues du principal régulateur de vernalisation VRN1 et des COR gènes incluant une protéine antigel et une lipocaline induite par la température (TIL). Nos résultats démontrent que les cultivars de printemps se comportent plutôt comme des cultivars facultatifs puisque leur contenu en osmoprotectants ainsi que les transcrits COR s'accumulent au froid. Les cultivars d'hiver ont atteint la vernalisation maximale après 49 jours au froid et ont accumulé plus de transcrits COR. Toutefois, aucune différence n'a été observée dans le contenu en osmoprotectants des cultivars de printemps et d'hiver. Afin d'augmenter la tolérance au gel du cultivar de printemps Bd21, des lignées transgéniques surexprimant une TIL ont été générées. Cette étude valide l'utilisation de Brachypodium comme modèle pour l'étude de la tolérance au gel chez les céréales de climat tempéré.

T-DNA and chemically mutagenized rice lines were used in a reverse genetic approach to investigate the role(s) of small RNA in rice, Oryza sativa L. T-DNA tagged lines of the RNA-dependent RNA polymerase 6 (Osrdr6) were homozygous lethal. However, a T-DNA line with disrupted expression of the gene encoding Suppressor of Gene Silencing3 (SGS3) and, also, a chemically mutagenized line with a single nucleotide polymorphism (SNP) in the intronic 2 region of this gene were characterized. Homozygous Ossgs3 mutant lines showed abnormal leaf curling. This suggests that these lines are hyperresponsive to auxin since they do not produce ta-siRNA, which is involved in the targeting and degradation of the Auxin Response Factor, leading to changes in leaf morphology. The homozygous Ossgs3 SNP mutant shows an increased sensitivity to the rice blast strain BNIII. This finding suggests that small RNA's, also, target and degrade fungal mRNA transcripts, decreasing pathogen virulence.
L'ADN-T ainsi que des lignées de riz chimiquement muté ont servi dans une approche de génétique inverse qui cherchait à élucider le(s) rôle(s) des petits ARNs du riz (Oriza sativa L.). La forme homozygote de l'ARN polymérase ARN-dépendante 6 (Osrdr6), étiquetée par ADN-T s'est avérée mortelle pour les lignées. Cependant, une lignée d'ADN-T avec une expression perturbée du gène encodant le «suppresseur du silençage génique» (SGS3) ainsi qu'une lignée chimiquement mutée avec un polymorphisme d'un seul nucléotide (SNP) dans la région intronique 2 de ce gène ont été caractérisées. Les lignées homozygotes Ossgs3 présentaient des feuilles anormalement bouclées. Le mutant homozygote SNP d'Ossgs3 présentait une sensibilité augmentée à la lignée BNIII du champignon pathogène du riz.

Context: Approximately one billion people live in semi-arid and arid regions, and of these about 40% live on less than a dollar a day. Legumes crops are an important component of sustainable agriculture, but they are often grown under intermittent or terminal droughts. Thus, improving drought tolerance in legumes has the potential to improve food security and sustainability of agricultural systems. Objective: This study compares the response of two legume crops, common bean (Phaseolus vulgaris L.) and mungbean (Vigna radiata (L.) Wilczek), to water stress conditions under field and controlled-environment conditions. Methods: Field experiments were conducted in the Fergana valley, Uzbekistan, and controlled environment experiments were conducted at the Macdonald campus of McGill University, Ste-Anne-de-Bellevue, Canada, and at the Hermitage Research Station in Warwick, Australia. Results: Our results demonstrate that alternate furrow irrigation maintains yields, yet decreases water applied by 25%. In addition, mungbean showed the highest yields in the moderate deficit irrigation treatment in 2003 and severe deficit irrigation treatment in 2004 under field conditions in Uzbekistan. Common bean also showed a capacity to maintain yields under moderate deficit irrigation in both years. Further characterization of the legume responses to water deficit stress in controlled-environment experiments indicated that mungbean’s higher tolerance is attributable to higher transpiration efficiency, a more conservative water use in the vegetative stage, and a higher root-to-shoot ratio when compared to common bean. Root characteristics might also play an important role, although we have observed a large variability between genotypes. An additional field experiment in Uzbekistan demonstrated that an early maturing Canadian soybean cultivar could be grown after the harvest of winter wheat, and thus contribute to food security. It has also been demonstrated that i
Contexte : Environ un milliard de personnes vivent dans les régions arides et semi-arides, et 40% d’entre eux vivent avec moins d’un dollar par jour. Les cultures de légumineuses sont une part importante de l’agriculture durable, mais ces cultures sont souvent produites dans des conditions de sécheresse intermittente ou terminale. Améliorer la tolérance des légumineuses à la sécheresse peut donc augmenter la sécurité alimentaire et la durabilité des systèmes agricoles. Objectif : Cette étude compare la réponse de deux légumineuses, le haricot commun (Phaseolus vulgaris L.) et le haricot doré (Vigna radiata (L.) Wilczek), lors de conditions de stress hydrique imposées au champ et en environnement contrôlé. Méthodes : Les expériences au champ furent conduites dans la vallée de Fergana, en Ouzbékistan, et les expériences en environnement contrôlé furent conduites au campus Macdonald de l’Université McGill, à Ste-Anne-de-Bellevue, Canada, et à la station de recherche Hermitage, à Warwick, Australie. Résultats : Nos résultats démontrent que l’irrigation alternante maintient les rendements tout en diminunant de 25% l’apport en eau. De plus, le haricot doré a démontré les meilleurs rendements sous les traitements d’irrigation déficitaire moyen en 2003 et sévère en 2004 dans les expériences au champ. Le haricot commun a également démontré la capacité de maintenir ses rendements sous traitement d’irrigation déficitaire moyen les deux années. Une caractérisation plus poussée de la réponse des légumineuses au stress hydrique en milieu contrôlé a indiqué que la tolérance accrue du haricot doré est attribuable à une meilleure efficacité transpirationelle, une utilisation plus limitée de l’eau lors de la période végétative, et une proportion plus élevée de biomasse en racines lorsque comparé au haricot commun. Les caractéristiques racinaires semblent également jouer un rôle important,$

'Honeycrisp', a new apple cultivar, has high susceptibility to physiological disorders, including soft scald (SS) and soggy breakdown (SB). An important factor inducing these disorders is cool weather conditions at the end of the growing season. 'Honeycrisp' apples were harvested in Ontario (three sites), Québec (two sites) and in Nova Scotia (one site), in 2009 and 2010, in addition to data from Ontario (four sites), from 2002 to 2006. Analyses were made to link fruit quality to the weather at each site. A combination of dry conditions (for phenological stages BBCH 71-75), and cool conditions (BBCH 65-71 and 77.5-80) increased SS susceptibility. A combination of cool and wet conditions (BBCH 77.5-80) increased SB susceptibility. Models were developed for SS (RMSE = 18.71) and SB (RMSE = 6.88) predictions. Producers could use these in establishing more appropriate management of fresh fruit loads depending on regional and seasonal susceptibility to these disorders.
'Honeycrisp', une nouvelle variété de pommes, est susceptible à l'échaudure molle (ÉM) et au brunissement interne (BI). Des conditions froides à la fin du développement des pommes induiraient leur développement. Des 'Honeycrisp' ont été récoltées en Ontario (trois sites), au Québec (deux sites) et en Nouvelle-Écosse (un site), en 2009 et 2010, avec l'ajout de données de l'Ontario (quatre site) entre 2002 et 2006. Des analyses ont été faites pour lier la qualité des pommes aux conditions météorologiques. Une combinaison de conditions sèches (aux stades phénologiques BBCH 71-75) et de températures froides (BBCH 65-71 et 77.5-80) augmenterait l'incidence d'ÉM, alors que des conditions froides et de fortes précipitations (BBCH 77.5-80) intensifierait le BI. Deux modèles de prédiction ont été développés pour l'ÉM (RMSE = 18.71) et le BI (RMSE = 6.88). Ceux-ci peuvent servir d'outils aidant les producteurs à élaborer une stratégie de mise en marché appropriée, selon les conditions régionales et saisonnières.

Nitrogen (N) and the levels of N in plants play a vital role in the physiology, regulating their development and metabolism. We grew Arabidopsis thaliana under agronomic conditions at low (6 mg N/L) and high (106 mg N/L) N fertilizer regimes, maintaining a constant NO3-N to NH4-N ratio (3:1). Using a shotgun mass spectrometry proteomics approach, multi-dimensional protein identification technology (MudPIT), we characterized a total of 2134 reproducibly identified proteins shared between the two N treatments. By statistical analysis in both treatments we found 37 differentially expressed proteins that satisfied both the AC test and the FDR q-value specified cutoffs, where 18 proteins were down regulated and 19 proteins were up regulated under low and high N treatments. We also found 35 differentially expressed proteins that are statistically important but did not satisfy the q- test. These differentially expressed proteins appear to have roles in glycolysis, metabolic, developmental, and signaling processes, or protein binding, transport and nucleic acid binding. The proteins associated with glycolysis indicate glutamine metabolism is of major importance in the plant N economy since it provides N to young developing tissues. Our study indicates that under varying N level treatments, proteins responsible for glutamate synthase (GOGAT), glutamine synthase (GS), and dehydrogenase activity (DH) that serve as enzymes to catalyze a link between carbohydrate and amino acid metabolism are up regulated. Thus, this study has enabled us to apply comparative shotgun proteomics to characterize A. thaliana at the proteomic level and will provide the tools necessary to provide an improved understanding of how and what up-regulates and down regulates different proteins under varying environmental conditions.
La fertilisation en azote (N) et la teneur en N des plantes ont un rôle clef dans leur physiologie, régulant leur développement et métabolisme. Tout en gardant un rapport de NO3-N à NH4-N de 3:1, des plants d'Arabidopsis thaliana (L.) Heynh furent cultivés sous deux régimes de fertilisation: bas (6 mg N/L) et élevé (106 mg N/L). Utilisant une technique protéomique en vrac par spectrométrie de masse et une technologie d'identification multidimensionnelle des protéines (MudPIT), nous avons pu caractériser un total de 2134 protéines identifiées de façon récurrente comme apparaissant dans les deux traitements de fertilisation azotée. Une analyse statistique des deux traitements a indiqué la présence de 37 protéines différentiellement exprimées, satisfaisant à la fois le test Audic-Claverie (AC) et le seuil de valeur q dans l'estimation du taux d'erreur (FDR). De celles-ci, 18 protéines furent régulées à la baisse lors des traitements à haut ou bas niveau de N, et 19 furent régulées à la hausse dans les mêmes circonstances. En plus, 35 protéines différentiellement exprimées du point de vue statistique ne passèrent tout de même pas le test de la valeur q. Les protéines différentiellement exprimées semblent avoir des rôles dans les processus de glycolyse, de métabolisme, de développement, de signalisation, et de transport, ainsi que dans la liaison des protéines et des acides nucléiques. Une analyse des protéines associées à la glycolyse indique que le métabolisme de la glutamine est d'une importance majeur dans l'économie en N de la plante, puisqu'il fournit l'azote aux jeunes tissus en voie de développement. Notre étude indique que, sous différents niveaux de fertilisation en N, les protéines responsables pour l'activité glutamate synthétase (GOGAT), glutamine synthétase (GS), et déshydrogénase (DH), servant comme enzymes dans la catalyse du lien entre les voies de métabolisme des glucides et celui des acides aminés, sont régulés à la hausse. Ainsi, cette étude nous permettra d'utiliser une technique protéomique en vrac comparative afin de caractériser A. thaliana au niveau protéomique, et nous fournira les outils nécessaires à mieux comprendre quelles protéines sont régulées à la hausse ou à la baisse sous différentes conditions environnementales et comment cette régulation est mise en œuvre.