Tesi sul tema "Flowering"

Les plantes ont longtemps intrigué les scientifiques, qui, avec son importance vitale pour la planète, sa beauté et l'énorme quantité de formes ayant, les rend un sujet attrayant pour la recherche. Un aspect intéressant est la création d'un modèle virtuel capable de simuler de vraies plantes avec un degré élevé de précision. L'objectif de notre étude est les plantes à fleurs, qui jouent un rôle énorme dans notre vie de fins nutritives et médicales à l'embellissement de l'environnement . L'obtention d'un modèle géométrique exacte d'une fleur est très utile, car elle joue un rôle important dans la validation du modèle virtuel. Par ailleurs, la visualisation de paramètres non directement traçables dans les plantes à fleurs vivantes est d'une grande aide à l'étude de la physiologie. L'énorme biodiversité entre les différentes parties d'un spécimen et entre les différents spécimens fournit une vaste zone d'objectifs qui la synthèse d'image doit contester. Modéliser des fleurs est un sous-ensemble d'un espace de recherche beaucoup plus vaste que la modélisation de plantes. Les plantes à fleurs ont des caractéristiques structurelles qui les rendent différentes des structures d'arbres, d’arbustes ou de l’herbe. A ce jour, on ne tient pas une grande importance à essayer cette ligne de recherche d'une façon particulière et en général a été classé dans le contexte plus large de la modélisation des plantes. Nous avons choisi d’utiliser le «L-systems» pour la procédure de la modélisation, et comme base pour notre recherche. Il y a différents mécanismes de catégorisation topologie de la plante dans chacune des étapes de sa croissance. Pour construire le plan de la structure d'une plante, avec une courte grammaire, quelques lignes étaient quelque chose qui dès le premier moment a suscité l'intérêt et par la suite évolué en quelques systèmes d'interprétation géométriques pour la modélisation des plantes. Notre objectif est d'étudier les moyens efficaces de décrire la structure des plantes à fleurs en utilisant L-systems. Tout d'abord, nous proposons de représenter les formes des feuilles, pétales, étamines, carpelles, etc. Avec une extension de L-systems - un modèle basé sur trois cartes généralisées dimensions - 3Gmaps L-systèmes, qui peut être appliquée avec succès pour la modélisation des plantes à fleurs. La description de la grammaire de la structure des plantes à fleurs fournit un nombre illimité de ses interprétations géométriques. Deuxièmement, nous allons améliorer le processus d'écriture de la grammaire par l'ajout d'une nouvelle fonctionnalité de paramétrage interactif. Troisièmement, nous allons proposer une nouvelle méthode de modélisation inverse des plantes à fleurs, où l'utilisateur peut définir de manière interactive les caractéristiques des fleurs. L'algorithme utilise cette information comme une entrée, qui est ensuite analysée et codée en tant que L -systèmes grammaire. Enfin, nous allons présenter une méthode pour créer des clairières de fleurs virtuelles à l'aide de gestes Kinect. Nous voulons faire remarquer que notre travail a été fait avec la plateforme de logiciel 3Gmaps L- système développé dans le cadre de la thèse d'intégrer toutes les techniques proposées
Plants have always intrigued scientists as besides of its sheer importance for the earth, their beauty and enormous variety of shapes tempt to thoroughly inquire about its nature. One of the aspects of this inquiry is the creation of the virtual model in order to mimic real plants to a high degree of accuracy. The focus of our study is the flowering plants, which play a huge role in our life from nutritive and medical purposes to beautifying the environment. Obtaining an accurate geometrical model of a flower is quite useful as it plays an important role in the validation of the virtual model. Besides, the visualization of parameters not traceable directly in living flowering plants is a stand-by in studying their physiology. A huge biological diversity both within and between individuals provides a vast area of objectives which the image synthesis must challenge.Flower modelling constitutes a part of a larger research area, plant modelling. Flowering plants have their particular structural features which are different from the structure of trees, bushes or grass. Still not a lot of emphasis has been placed to date on this problem, as it was categorized within the modelling of plants in general. We chose a procedural modeling using L-systems as a base of our research. L-system is a very powerful method of plant simulation. It provides a means of characterizing the topology of a plant at every stage of its growth. Grasping the plant structure with just several lines of grammar attracted immediate interest and later on evolved into several powerful geometrical interpretation system used in plant modelling. Our purpose is to study efficient ways of describing the structure of flowering plants by means of L-systems. First, we will propose to represent the shapes of leafs, petals, stamens, carpels, etc. with an extension of L-systems – a model based on three dimensional generalized maps – 3Gmaps L-systems, which can be successfully applied for the modelling of flowering plants. The grammar description of the structure of the flowering plants provides an unlimited number of its geometrical interpretations. Second, we will improve the process of grammar writing by adding a new functionality of interactive parameter adjustment. Third, we will propose a new method of inverse modelling of flowering plants, where the user can interactively define the flower characteristics. The algorithm uses this information as an input, which is then analyzed and coded as L-systems grammar. Finally, we will present a method for creating virtual glades of flowers using Kinect gestures. We want to remark that our work has been done with 3Gmaps L-system software platform developed in the scope of the thesis to integrate all the proposed techniques

The proportion of resources which an organism devotes to reproduction has been assumed to be of great evolutionary and ecological significance. However, in previous studies of reproductive allocation (RA) in plants, there has been no consensus of precisely what is being measured nor how it should be measured. An attempt was made to determine the 'best' method of measuring RA and then apply this to a range of species with differing ecological strategies. Under nutrient stress caused by a low N treatment Taraxacum officinale and Poa annua were found to maintain their RA despite up to 4 fold reductions in biomass. Under K and P deficient conditions there was a preferential allocation of these elements to reproductive structures in Taraxacum. Ruderal plants therefore, seem to maintain biomass RA and seed quality despite nutrient stress. Although the nutrient RA in Taraxacum was found to be significantly different from biomass RA (KRA = 71% PRA = 66% BRA= 51.7%) the extent of the difference varied between treatments. There was therefore no obvious alternative currency to biomass. The evolutionary consequences of reproduction may also be measured through a reproductive cost which may take the form of reduced future reproduction, survival or growth. Prevention of flowering in Digitalis purpurea resulted in an increase in the number of axillary buds produced, Similarly in Plantago lanceolata removal of flowers resulted in a 3 fold increase in production of buds. In both species realisation of a reproductive cost was prevented. The importance of individual variability was noted. The importance of plant morphology was evident and was used to explain some of the anomalous RA values in the comparative experiment. RA values were collected for 40 species of Gramineae. RA was a useful ecological index which emphasised the ruderal element of a plant's strategy. When used in conjunction with other parameters particularly Rmax, RA produced a meaningful classification of species in terms of their ecological strategy.

Thesis (PhD(Agric))--University of Stellenbosch, 2000.
ENGLISH ABSTRACT: Little is understood regarding flowering in the genus Protea. The information available on inflorescence initiation and development in the family Proteaceae was reviewed and discussed. A number of experiments were conducted to investigate inflorescence initiation and development, and their manipulation for commercial production, in selected Protea cultivars, in the Western Cape, South Africa (33°S, Protea species can be allocated into groups according to similar times of flower initiation and of harvest. The stages occurring during flower initiation, and their synchrony relative to shoot growth were investigated for three cultivars, viz. Protea cv. Carnival (P. compacta x P. neriifolia), Protea cv. Lady Di (P. compacta x P. magnifica) and Protea cv. Sylvia (P. eximia x P. susannae), when flower initiation occurred on the spring growth flush. For all three cultivars the spring flush was preformed and enclosed in the apical bud before spring budbreak. During elongation of the spring flush the apical meristem produced floral primordia which differentiated into involucral bracts. After completion of the spring flush meristematic activity continued, to produce floral bracts with florets in their axils. The three cultivars showed differences and similarities in the time of budbreak, and the rates of shoot growth, appendage formation and flower development. The presence of mature leaves on an over-wintering shoot is essential for inflorescence initiation on the spring growth flush of 'Carnival'. Inflorescence initiation in 'Carnival' started at spring budbreak, and production of involucral bracts occurred concurrently with spring flush elongation. Shoots were defoliated at different degrees of severity at intervals from pre- to post- spring budbreak. Total defoliation applied earlier than 6-7 weeks before spring budbreak prevented flowering. Defoliation closer to spring budbreak affected characteristics of the spring flush and the inflorescence subtended by the spring flush. Effects were most marked following total defoliation and diminished with less severe treatments imposed by partial defoliation. Total defoliation applied before spring budbreak resulted in slower inflorescence development and lead to later anthesis. Defoliation treatments applied after completion of spring flush elongation had no effect on either vegetative or reproductive spring growth. The requirement for mature overwintering leaves to effect inflorescence initiation in 'Carnival' suggests that environmental factors, such as low temperature and daylength may play an inductive role. Shoots were in the induced state and committed to flowering 6-7 weeks before spring budbreak. A change in source size and position subsequent to different severalties of defoliation in 'Carnival' lead to reduced dry mass accumulation and altered partitioning. Mature leaves on the overwintering shoot supported growth of the spring flush and the early stages of inflorescence development. When these leaves were removed by total defoliation dry mass accumulation in the spring flush was reduced. A hierarchy of priorities between competing sinks was revealed by defoliation during growth of the spring flush and concomitant inflorescence development: formation of involucral bracts> leaf growth> stem elongation. Dry mass accumulation of the inflorescence subtended by the spring flush was supported by the spring flush leaves and was only indirectly affected by defoliation. Treatments which resulted in the production of a weaker spring flush lead to a reduction in dry mass accumulation of the inflorescence. Different severalties of partial defoliation, whereby either upper or lower leaves were removed from a shoot, indicated that the position of leaves relative to the active sink is more important, with respect to source availability, than the number of leaves on the shoot. Mature overwintering leaves are essential in 'Lady Di' for shoots to achieve the induced state for flowering; and are also crucial to the early stages of inflorescence initiation. Defoliation applied before formation of involucral bracts was complete prevented flowering. Defoliated shoots either remained vegetative or produced inflorescences which aborted. Reserve carbohydrates in the stem and leaves of overwintering shoots were low, and early growth and development of both the spring flush and inflorescence were, therefore, supported by current photosynthates from the overwintering leaves. Likewise, reserve carbohydrates available in the flowering shoot were insufficient to account for the dry mass increase during the major portion of growth of the spring flush and inflorescence. This rapid increase in dry mass occurred after elongation of the spring flush was complete and was supported by current photosynthates from the leaves of the spring flush. Defoliation treatments that did not prevent inflorescence initiation, had no effect on inflorescence development, and flowering time of 'Lady Di' was not delayed by defoliation. 'Sylvia' has an open window for inflorescence initiation and can initiate flowers throughout the year. Despite the 'open window' inflorescences are initiated more readily on the spring flush, when it is subtended by one or more overwintering shoots. This may be the expression of a facultative response to inductive conditions for which 'Carnival' and 'Lady Di' have an obligate requirement. The date of pruning affected flowering time of 'Sylvia' by influencing on which flush inflorescence initiation occurred, and the harvest could be manipulated to fall within the optimum marketing period for export to Europe. Flowers initiated on the spring flush reach anthesis in January and February; on the first summer flush predominantly in April and May; on the second summer flush in July and August; and on the autumn flush in November and December. Thus, shoots harvested within the optimum marketing period (September to February) initiated inflorescences on the autumn and spring flushes. Due to the readiness of shoots to initiate inflorescences on the spring flush many shoots harvested in January and February (following initiation in the previous spring) were short and were rendered unmarketable. For commercial production pruning in July is recommended. Long flowering stems will be harvested in October to November of the following year. Since the vegetative and reproductive cycles necessary to produce inflorescences on long stems span more than a year, a biennial cropping system is recommended.
AFRIKAANSE OPSOMMING: Bloeiwyse-inisiasie en -ontwikkeling, en die manipulasie daarvan, van geselekteerde cultivars van die genus Protea. Min word verstaan van blomvorming in die genus Protea. Die beskikbare inligting oor die bloeiwyse-inisiasie en -ontwikkeling in die familie Proteaceae is nagegaan en bespreek. 'n Aantal eksperimente is uitgevoer waarin geselekteerde Protea cultivars van die Wes-Kaap, Suid-Afrika (33°S, 19°0) se bloeiwyse-inisiasie en -ontwikkeling, asook die manipulasie daarvan vir kommersiële produksie ondersoek is. Protea spesies kan in groepe ingedeel word op grond van blominisiasietye en oestye wat ooreenstem. Die verskillende stadiums van blominisiasie en hulle sinchronisering relatieftot stingelgroei is ondersoek vir drie kultivars, naamlik Protea cv. Carnival (P. compacta x P. neriifolia), Protea cv. Lady Di (P. compacta x P. magnifica) en Protea cv. Sylvia (P. eximia x P. susannae) tydens blominisiasie op die lentegroeistuwing. By al drie die kultivars was die lentegroeistuwing reeds gevorm en omsluit in die apikale knop voor die lente-knopbreking. Gedurende die verlenging van die lentegroeistuwing het die apikale meristeem blomprimordia, wat in bloeiwyseomwindselskutblare gedifferensieer het, geproduseer. Na voltooiing van die lentegroeistuwing, het meristematiese aktiwiteit voortgeduur en blomskutblare met blommetjies in hulle oksels is gevorm. Die drie kultivars het verskille en ooreenkomste vertoon tydens die periode van knopbreking, asook in die tempo van stingelgroei, aanhangselformasie en blomontwikkeling. Die teenwoordigheid van volwasse blare op 'n oorwinteringstingel is noodsaaklik vit bloeiwyse-inisiasie op die lentegroeistuwing van 'Carnival'. Bloeiwyse-inisiasie in 'Carnival' het met lente-knopbreking begin en die produksie van bloeiwyseomwindselblare het gelyktydig met lentegroeistuwing verlenging plaasgevind. Stingels is met tussenposes, van voor tot na die lente-knopbreking, en met verskillende grade van felheid, ontblaar. Algehele ontblaring vroeër as 6-7 weke voor die lente-knopbreking het blomvorming verhoed. Ontblaring nader aan die lenteknopbreking het 'n invloed gehad op die eienskappe van die lentegroeistuwing asook die bloeiwyse gedra deur die lentegroeistuwing. Die effek was die duidelikste sigbaar by algehele ontblaring en het verminder namate die behandeling minder fel geword het by gedeeltelike ontblaring. Algehele ontblaring wat voor die lente-knopbreking gedoen is, het gelei tot stadiger bloeiwyse-ontwikkeling en later antese. Ontblaringsbehandelings wat na die voltooiing van die lentegroeistuwing verlenging toegepas is, het geen effek op die vegetatiewe of die reproduktiewe lentegroei gehad me. Die nodigheid van volwasse oorwinteringsblare vir bloeiwyse-inisiasie in 'Carnival' dui daarop dat omgewingsfaktore soos lae temperature en daglengte 'n induktiewe rol kan speel. Stingels was in die geïnduseerde toestand en verbind tot blomvorming 6-7 weke voor die lente-knopbreking. 'n Verandering in oorspronggrootte en -posisie as gevolg van verskille in die felheid van ontblaring by 'Carnival', het gelei tot verminderde droë-massa-akkumulasie en veranderde verdeling. Volwasse blare op die oorwinteringstingel het die groei van die lentegroeistuwing en die vroeë stadiums van bloeiwyse-ontwikkeling ondersteun. Toe hierdie blare verwyder is in 'n algehele ontblaring, het die droë-massa-akkumulasie in die lentegroeistuwing verminder. 'n Hiërargie van prioriteite tussen kompeterende sinke is blootgelê tydens ontblaring gedurende die lentegroeistuwing en saamlopende bloeiwyse-ontwikkeling: vorming van bloeiwyse-omwindselblare > blaargroei > stamverlenging. Droë-massa-akkumulasie van die bloeiwyse onderspan deur die lentegroeistuwing is ondersteun deur die blare van die lentegroeistuwing en is slegs op 'n indirekte wyse deur ontblaring geaffekteer. Behandelings wat tot die produksie van 'n swakker lentegroeistuwing gelei het, het tot 'n vermindering in die droë-massaakkumulasie van die bloeiwyse gelei. Verskille in die felheid van gedeeltelike ontblaring, waartydens óf die boonste óf die onderste blare van 'n stingel verwyder is, het aangetoon dat die posisie van die blare relatief tot die aktiewe sink belangriker is, met betrekking tot die beskikbaarheid van die oorsprong, as die aantal blare op die stingel. By 'Lady Di' is volwasse oorwinteringsblare noodsaaklik VIr stingels om die geïnduseerde stadium van blomvorming te bereik en hulle is ook van die uiterste belang in die vroeë stadiums van bloeiwyse-inisiasie. Waar ontblaring gedoen is voordat die vorming van bloeiwyse-omwindsel voltooi was, het blomvorming nie plaasgevind nie. Ontblaarde stingels het ófvegetatief gebly ófbloeiwyses geproduseer wat geaborteer het. Reserwe-koolhidrate in die stam en blare van die oorwinteringstingels was laag en die vroeë groei en ontwikkeling van beide die lentegroeistuwing en die bloeiwyse is dus deur die bestaande fotosintate van die oorwinteringsblare onderhou. Net so was die reserwe-koolhidrate beskikbaar in die blomdraende stingels nie voldoende om die toename in droë massa gedurende die grootste deel van die groei van die lentegroeistuwing en die bloeiwyse te verklaar nie. Hierdie vinnige toename in droë massa het plaasgevind nadat die verlenging van die lentegroeistuwing voltooi was en is deur die bestaande fotosintate van die blare van die lentegroeistuwing onderhou. Ontblaringsbehandelings wat nie bloeiwyse-inisiasie verhoed het nie, het geen effek op bloeiwyse-ontwikkeling gehad nie en die blomtyd van 'Lady Di' is nie deur ontblaring vertraag nie. 'Sylvia' beskik oor 'n oop venster vir bloeiwyse-inisiasie en kan regdeur die jaar blomme inisieer. Ten spyte van die 'oop venster', word bloeiwyses tog meer geredelik in die lentegroeistuwing geïnisieer, wanneer dit deur een of meer van die oorwinteringstingels gedra word. Dit mag die uitdrukking wees van 'n fakultatiewe respons op induktiewe toestande wat vir 'Carnival' en 'Lady Di' 'n verpligte vereiste is. 'Sylvia' se blomtyd is deur die snoeidatum geaffekteer omdat die snoeidatum 'n invloed gehad het op die keuse van by watter groeistuwing bloeiwyse-inisiasie plaasgevind het. Die oestyd kon gemanipuleer word om binne die optimum bemarkingstydperk vir uitvoer na Europa te val. Blomme wat op die lentegroeistuwing geïnisieer is, bereik antese in Januarie en Februarie; dié wat op die eerste somergroeistuwing geïnisieer is, bereik antese hoofsaaklik in April en Mei; dié wat op die tweede somergroeistuwing geïnisieer is, bereik antese in Julie en Augustus en dié wat op die herfsgroeistuwing geïnisieer is, bereik antese in November en Desember. Stingels wat in die optimum bemarkingsperiode (September tot Februarie) geoes is, het dus bloeiwyses op die herfs- en lente-groeistuwings geïnisieer. As gevolg van die gereedheid van stingels om bloeiwyses op die lentegroeistuwings te inisieer, was baie van die stingels wat in Januarie en Februarie geoes is, kort en kon nie bemark word nie. Vir kommersiële doeleindes word snoei in Julie aanbeveel. Lang blomdraende stingels sal in Oktober en November van die volgende jaar geoes word. Aangesien die vegetatiewe en reproduktiewe siklusse wat nodig is om bloeiwyses met lang stingels te produseer oor meer as fn jaar strek, word fn tweejaarlikse oesinsamelingstelsel aanbeveel.

Analysis of photomorphogenic mutants and transgenic plants provides further insights into the roles of individual phytochrome species. The presence of a significant early-flowering response to low R/FR ratio has been reveled in Arabidopsis phyB mutants, that are also homozygous for a late-flowering mutation. This firstly, implicates at least one other novel phytochrome species, in addition to phytochrome B, in the low R/FR ratio-mediated early- flowering response. Secondly, identifies features that are likely to represent a loss-of-function mutant in this novel phytochrome species. Examination of the Arabidopsis elg mutant, a putative novel phytochrome loss-of- function mutant, defines ELG as a novel gene that influences elongation growth. What is more, ELG appears to act independently of phytochrome and GA. However, H4S seedlings overexpress the Arabidopsis HAT4 transgene, which is proposed to be down-regulated by a novel phytochrome. Thus, physiological analysis of Arabidopsis H4S seedlings reveal characteristics that may be representative of seedlings with a deficiency in a novel phytoclirome species. The physiological effects of phytochrome overexpression have also been examined in DN and SD N. tabacum, cv. Hicks. Allelic series overexpressing phytochrome A, phytochrome B and phytochrome C were generated for this purpose. These analyses provide a full characterisation of a phytochrome B-overexpression phenotype in tobacco, previously unreported. They also provide the first evidence that phytochrome C is a functional photoreceptor, and the first description of a phytochrome C-overexpression phenotype. DN and SD N. tabacum differ only with respect to the MM locus, which confers SD photoperiodicity. Hence, these plants are ideally suited for the comparative analysis of phytoclirome overexpression on photoperiodic perception. Alterations in the NB-mediated flowering response in transgenic plants suggests that phytochrome A- and B-overexpression disrupt photoperiodic timimg. However, the behaviour of N. tabacum overexpressing phytochrome C suggests that the phytochrome C transgene may specifically affect MM transduction.

Flowering plants exhibit a particular pattern of seasonal cycle to suit the changing seasons for maximum survival and reproduction success. Temperature plays a key role in controlling flowering time of many plants. Fragaria vesca f. vesca is seasonal flowering and runnering. While it is not known to require vernalisation to flower, cool and cold temperatures affect its vegetative and reproductive development. An F. vesca VIN3-like (FvVIL) mRNA was isolated and characterised. It has a PHO finger domain, a FNIII domain and a VIO domain, which characterise the VIN3 family genes of Arabidopsis thaliana. It contains four exons, and it is more similar to VIL2 than other VIN3 family genes of Arabidopsis thaliana.• The coding sequence of FvVIL contains 2208 nucleotides; six and nine nucleotides less than that of Prunus persica and Malus x domestica respectively with 78% identical. In experiments to develop a transformation system, F. v. semperflorens had higher in vitro regeneration than F. vesca. Both species could not regenerate from either leaf or petiole segments on medium without plant growth regulators. Plantlet regeneration from leaf explants was better at 1 mg L-1 than 2, 3 and 4 mg L-1 BAP. Plantlet regeneration from F. v. semperflorens petiole explants was best achieved at 0.1 mg L-1 IBA compared to 0, 0.2 and 0.4 mg L-1. F. vesca initiated flowers after eight weeks at 12°C under 8h short-days (SO). Plants chilled at 4°C produced fewer leaves than plants chilled at 8 or 12°C. Extended exposure to cool or chill temperature promoted more synchronised vegetative growth than a shorter exposure. Prolonged cool temperature promoted petiole elongation more than a short period of chilling. Extended chilling at 4°C for eight weeks in SO greatly stimulated F. vesca runner production after transfer to 20°C long-day (LO) conditions. There was no evidence suggesting dormancy breaking had occurred. Chilling delayed the emergence of inflorescences in F. vesca. Flower initiation was stopped by prolonged chilling but not by a short period of chilling.

The angiosperm order Malpighiales includes \(\sim 16,000\) species and constitutes up to 40% of the understory tree diversity in tropical rain forests. Despite remarkable progress in angiosperm phylogenetics during the last 20 years, relationships within Malpighiales have remained poorly resolved, possibly due to its rapid rise during the mid-Cretaceous. Using phylogenomic approaches, including analyses of 82 plastid genes from 58 species, we identified 12 new clades in Malpighiales and substantially increased resolution along the backbone (Chapter 1). This greatly improved phylogeny revealed a dynamic history of shifts in net species’ diversification rates across Malpighiales, with bursts of diversification noted in the Barbados cherries (Malpighiaceae), cocas (Erythroxylaceae), and passion flowers (Passifloraceae). We also found that commonly used a priori approaches for partitioning data in similar large-scale analyses, by gene or by codon position, performed poorly relative to the use of partitions identified a posteriori using a Bayesian mixture model. Another aspect of my thesis focused on investigating horizontal gene transfer (HGT) in Malpighiales. Recent studies have suggested that plant genomes have undergone potentially rampant HGT. Parasitic plants have provided the strongest evidence of HGT, which appears to be facilitated by the intimate physical association between the parasites and their hosts. Using phylogenomic approaches, we analyzed the nuclear transcriptome (Chapter 2) and mitochondrial genome (Chapter 3) of the holoparasite Rafflesiaceae, which represents an enigmatic subclade of Malpighiales. Our analyses show that several dozen actively transcribed nuclear genes, and as many as 34–47% of its mitochondrial gene sequences, show evidence of HGT depending on the species. Some of these HGTs appear to have maintained synteny with their donor and recipient lineages suggesting that vertically inherited genes have likely been displaced via homologous recombination, as is common in bacteria. Finally, our results establish for the first time that although the magnitude of HGT involving nuclear genes is appreciable in these parasitic plants, HGT involving mitochondrial genes is substantially higher. Moreover, the elevated rate of unidirectional host-to-parasite gene transfer raises the possibility that HGTs may provide a fitness benefit to Rafflesiaceae for maintaining these genes.

Flowering is controlled by a series of signals integrated to regulate gene expression and coordinate development. The flowering hormone FLOWERING LOCUS T (FT) positively regulates flowering while the highly homologous TERMINAL FLOWERING 1 (TFL1) negatively regulates flowering. FT is recruited to the promoter in a complex with FD, a transcription factor belonging to the bZIP family, and 14-3-3. This complex is called flowering activating complex (FAC). Here TFL1 is shown to form a complex with 14-3-3 proteins and FD that has striking similarity to the FAC. By probing the extended loop of TFL1 a small region was identified towards the N-terminus of the loop that is involved in mediating the interaction with 14-3-3. This TFL1-14-3-3 platform can interact with the C-terminus of FD, and moreover this interaction occurs between FD and 14-3-3 rather than directly between FD and TFL1 as had been previously speculated. Results indicate that the TFL1-14-3-3 complex, but not FT-14-3-3, can interact with the AP1 promoter from Arabidopsis and that FD is not required for this interaction. In addition, we have located a region of three residues near the C-terminal portion of the loop that when mutated can convert FT from an activator of flowering into a strong repressor of flowering in vivo. Overall, the results suggest that TFL1 can associate with DNA and recruit FD to specific regulatory sites via 14-3-3 proteins, while FT is recruited via FD to a different region within the AP1 promoter region. The data thus provide the basis for a mechanistic model for the antagonistic functions of FT and TFL1 in regulating flowering.

Thesis (MSc)--University of Stellenbosch, 2005.
ENGLISH ABSTRACT: The aim of this study was to elucidate the control of flowering in Protea spp. The main factor that makes studying flowering in this diverse genus so challenging is the fact that most Protea spp. and their commercial hybrids have very dissimilar flowering times. The carbon input into floral organ formation and support is expensive as flowers from Protea spp are arranged in a very large ‘flowerhead’ (50 mm by 130 mm for ‘Carnival’) that can take up to two months to develop fully. Therefore the carbon needed for structural formation, metabolic respiration and the sugar-rich nectar production make these structures extremely expensive to form and maintain. Protea is a sclerophyllous, woody perennial shrub with a seasonal flush growth habit. The leathery leaves (source tissue) produce most of the carbon needed for support and growth of the new leaves, roots and flowers (sink tissue). In the case of expensive structures, such as the inflorescences, remobilization from stored reserves, probably from underground storage systems, can be observed for structural development and maintenance. At all times the flush subtending the apical meristem or florally developing bud provides the largest proportion of carbon for support of the heterotrophic structures. Protea apical meristems stay dormant during the winter months, but BA (benzyl adenine, 6-benzylaminopurine) application to the apical meristem of the Protea hybrid ‘Carnival’ has shown to be effective in the release of dormancy and subsequently shift flowering two months earlier than the natural harvesting time. BA is thought to shift source/sink relationships by stimulating the remobilization of carbon to the resting meristem. Although no direct evidence was found for this in our assay, possible reasons for a weak assay are discussed. This study combined physiological research with the use of molecular tools. An homologue of the Arabidopsis thaliana meristem identity gene, LEAFY, was identified in Proteaceae. PROFL (PROTEA FLORICAULA LEAFY) is expressed in both vegetative and reproductive meristems as well as leaves. PROFL expression in leaves may have an inhibitory effect on vegetative growth, as the expression was high at the same time as the expression in the apical meristem increased marking the transition to reproductive growth. In perennial species such as Protea, the availability of carbon is thought to be the main factor controlling floral development. Possible mechanisms of control may be through the direct control of meristem identity genes such as PROFL through sugar signaling. BA did not have a direct effect on PROFL expression although the expression pattern was one month in advance when compared to the natural system. PROFL expression seems to be consistent with that found for other woody perennial species and would therefore be a convenient marker for floral transition.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die inisiëring van blomvorming in Protea spp. te ondersoek. Die verskil in blomtyd tussen Protea spp. en hul kommersieel ontwikkelde hibriede maak die studie van hierdie genus ‘n groot uitdaging. Die groot hoeveelheid koolstof wat benodig word vir blomvorming in Protea is hoofsaaklik as gevolg van die grootte (50 mm by 130 mm vir ‘Carnival’) van die blomkop waarin individuele blomme geranskik is. Hierdie blomkoppe kan tot 2 maande neem om volwassenheid te bereik. Die koolstof benodig vir strukturele ontwikkeling, metaboliese respirasie en produksie van suiker-ryke nektar maak die vorming van hierdie structure ongelooflik duur. Protea is ‘n bladhoudende, houtagtige bos met ‘n seisoenale groeipatroon. Die leeragtige blare voorsien die grootste hoeveelheid koolstof vir die ontwikkelende blare, wortels en blomme. Koolstof vir die ontwikkeling en ondersteuning van die groot stukture soos die blomkoppe word gedeeltelik deur die huidige fotosinfaat voorsien en bewyse vir die remobilisasie van gestoorde koolstof, heel waarskynlik vanaf ondergrondse stukture, is gevind. Die blare van die stemsegment wat die apikale meristeem of ontwikkelende blom dra, voorsien altyd die grootse hoeveelheid koolhidrate aan die ontwikkelende struktuur. Die apikale meristeme van Protea bly dormant gedurende die winter maande, maar applikasie van BA (bensieladenien, 6-bensielaminopurien) aan die apikale meristeme van die Protea hibried ‘Carnival’ verbreek dormansie en die blomtyd van hierdie gemanipuleerde plante is daarom twee maande vroeër as die natuurlike oestyd. Daar word gespekuleer dat BA applikasie aan die apikale meristeem die hoeveelheid koolstof wat na die dormante meristeem gestuur word verhoog wat dan die dormansie verbreek. Hierdie studie beproef ongelukkig hierdie hipotese swak en redes hiervoor word bespreek. In hierdie studie word fisiologiese analises met molekulêre studies gekombineer. ‘n Meristeem identiteits gene wat homologie wys met LEAFY (LFY) in Arabidopsis thaliana (Arabidopsis), PROFL (PROTEA FLORICAULA LEAFY), is in Proteaceae geïdentifiseer. PROFL word uitgedruk in reproduktiewe meristeme so wel as die vegetatiewe meristeme en blare. PROFL uitdrukking in blare mag dalk ‘n inhiberende effek hê op die vorming van nuwe blare, omdat die uitdrukking hoog was op die selfde tyd as wat blominisiëring plaasgevind het in die apikale meristeem. Die transisie tot reproduktiewe groei word gekenmerk deur ‘n verhoging in PROFL uitdrukking in die apikale meristeem. In meerjarige plante soos Protea spp word daar verwag dat die teenwoordigheid van voldoende koolstof die oorskakeling na reproduktiewe groei inisieer. Dit mag wees deur die direkte aksie van suikers met gene soos PROFL wat die finale skakel na reproduktiewe groei beheer. Alhoewel BA applikasie geen direkte effek gehad het op PROFL uitdrukking nie, was die blomtyd met twee maande vervroeg. PROFL uitdrukking was vergelykbaar met die uitdrukking van LFY homoloë in ander houtagtige, meerjarige plante en kan gebruik word as ‘n merker vir blominisiëring in Protea spp.

Effects of exogenously applied GA₄₊₇ on floral and vegetative development of Streptocarpus x hybridus were investigated. S. x hybridus 'Hybrid Delta' petiolode tissue from plants treated with 25 μg GA₄₊₇ were examined by scanning electron microscopy. Plants treated at 1 cm leaf lengths appeared unaffected by GA₄₊₇ one week after treatment while 2 and 3 cm GAâ treated samples showed enhanced floral initiation.

Master of Science

Box-Ironbark forests occur on the inland hills of the Great Dividing Range in Australia, from western Victoria to southern Queensland. These dry, open forests are characteristically dominated by Eucalyptus species such as Red Ironbark E. tricarpa, Mugga Ironbark E. sideroxylon and Grey Box E. microcarpa. Within these forests, several Eucalyptus species are a major source of nectar for the blossom-feeding birds and marsupials that form a distinctive component of the fauna. In Victoria, approximately 83% of the original pre - European forests of the Box-Ironbark region have been cleared, and the remaining fragmented forests have been heavily exploited for gold and timber. This exploitation has lead to a change in the structure of these forests, from one dominated by large 80-100 cm diameter, widely -spaced trees to mostly small (≥40 cm DBH), more densely - spaced trees. This thesis examines the flowering ecology of seven Eucalyptus species within a Box-Ironbark community. These species are characteristic of Victorian Box-Ironbark forests; River Red Gum E. camaldulensis, Yellow Gum E. leucoxylon, Red Stringybark E. macrorhyncha, Yellow Box E. melliodora, Grey Box E. microcarpa, Red Box E. polyanthemos and Red Ironbark E. tricarpa. Specifically, the topics examined in this thesis are: (1) the floral character traits of species, and the extent to which these traits can be associated with syndromes of bird or insect pollination; (2) the timing, frequency, duration, intensity, and synchrony of flowering of populations and individual trees; (3) the factors that may explain variation in flowering patterns of individual trees through examination of the relationships between flowering and tree-specific factors of individually marked trees; (4) the influence of tree size on the flowering patterns of individually marked trees, and (5) the spatial and temporal distribution of the floral resources of a dominant species, E. tricarpa. The results are discussed in relation to the evolutionary processes that may have lead to the flowering patterns, and the likely effects of these flowering patterns on blossom-feeding fauna of the Box-Ironbark region. Flowering observations were made for approximately 100 individually marked trees for each species (a total of 754 trees). The flower cover of each tree was assessed at a mean interval of 22 (+ 0.6) days for three years; 1997, 1998 and 1999. The seven species of eucalypt each had characteristic flowering seasons, the timing of which was similar each year. In particular, the timing of peak flowering intensity was consistent between years. Other spatial and temporal aspects of flowering patterns for each species, including the percentage of trees that flowered, frequency of flowering, intensity of flowering and duration of flowering, displayed significant variation between years, between forest stands (sites) and between individual trees within sites. All seven species displayed similar trends in flowering phenology over the study, such that 1997 was a relatively 'poor' flowering year, 1998 a 'good' year and 1999 an 'average' year in this study area. The floral character traits and flowering seasons of the seven Eucalyptus species suggest that each species has traits that can be broadly associated with particular pollinator types. Differences between species in floral traits were most apparent between 'summer' and 'winter' flowering species. Winter - flowering species displayed pollination syndromes associated with bird pollination and summer -flowering species displayed syndromes more associated with insect pollination. Winter - flowering E. tricarpa and E. leucoxylon flowers, for example, were significantly larger, and contained significantly greater volumes of nectar, than those of the summer flowering species, such as E. camaldulensis and E. melliodom. An examination of environmental and tree-specific factors was undertaken to investigate relationships between flowering patterns of individually marked trees of E. microcarpa and E. tricarpa and a range of measures that may influence the observed patterns. A positive association with tree-size was the most consistent explanatory variable for variation between trees in the frequency and intensity of flowering. Competition from near-neighbours, tree health and the number of shrubs within the canopy area were also explanatory variables. The relationship between tree size and flowering phenology was further examined by using the marked trees of all seven species, selected to represent five size-classes. Larger trees (≥40 cm DBH) flowered more frequently, more intensely, and for a greater duration than smaller trees. Larger trees provide more abundant floral resources than smaller trees because they have more flowers per unit area of canopy, they have larger canopies in which more flowers can be supported, and they provide a greater abundance of floral resources over the duration of the flowering season. Heterogeneity in the distribution of floral resources was further highlighted by the study of flowering patterns of E. tricarpa at several spatial and temporal scales. A total of approximately 5,500 trees of different size classes were sampled for flower cover along transects in major forest blocks at each of five sample dates. The abundance of flowers varied between forest blocks, between transects and among tree size - classes. Nectar volumes in flowers of E. tricarpa were sampled. The volume of nectar varied significantly among flowers, between trees, and between forest stands. Mean nectar volume per flower was similar on each sample date. The study of large numbers of individual trees for each of seven species was useful in obtaining quantitative data on flowering patterns of species' populations and individual trees. The timing of flowering for a species is likely to be a result of evolutionary selective forces tempered by environmental conditions. The seven species' populations showed a similar pattern in the frequency and intensity of flowering between years (e.g. 1998 was a 'good' year for most species) suggesting that there is some underlying environmental influence acting on these aspects of flowering. For individual trees, the timing of flowering may be influenced by tree-specific factors that affect the ability of each tree to access soil moisture and nutrients. In turn, local weather patterns, edaphic and biotic associations are likely to influence the available soil moisture. The relationships between the timing of flowering and environmental conditions are likely to be complex. There was no evidence that competition for pollinators has a strong selective influence on the timing of flowering. However, as there is year-round flowering in this community, particular types of pollinators may be differentiated along a temporal gradient (e.g. insects in summer, birds in winter). This type of differentiation may have resulted in the co-evolution of floral traits and pollinator types, with flowers displaying adaptations that match the morphologies and energy requirements of the most abundant pollinators in any particular season. Spatial variation in flowering patterns was evident at several levels. This is likely to occur because of variation in climate, weather patterns, soil types, degrees of disturbance and biotic associations, which vary across the Box-Ironbark region. There was no consistency among sites between years in flowering patterns suggesting that factors affecting flowering at this level are complex. Blossom-feeding animals are confronted with a highly spatially and temporally patchy resource. This patchiness has been increased with human exploitation of these forests leading to a much greater abundance of small trees and fewer large trees. Blossom-feeding birds are likely to respond to this variation in different ways, depending upon diet-breadth, mobility and morphological and behavioural characteristics. Future conservation of the blossom-feeding fauna of Box-Ironbark forests would benefit from the retention of a greater number of large trees, the protection and enhancement of existing remnants, and revegetation with key species, such as E. leucoxylon, E. microcarpa and E. tricarpa. The selective clearing of summer flowering species, which occur on the more fertile areas, may have negatively affected the year-round abundance and distribution of floral resources. The unpredictability of the spatial distribution of flowering patches within the region means that all remnants are likely to be important foraging areas in some years.

Delayed flowering has the potential to overcome the problem of restricted vegetative growth, prior to flowering, that is often associated with double-cropped soybeans [Grycine max (L.) Merr.]. Objectives were to study delayed flowering in soybeans as influenced by date of planting, to estimate the lengths of the component vegetative periods in soybeans under short-day conditions, and to study the mode of inheritance of delayed flowering in soybeans. Date of planting experiments conducted in the field at two Virginia locations using 27 cultivars and breeding lines showed that genotypic differences exist for delayed flowering, especially between delayed and normal flowering isolines. Lengths of the juvenile and inductive periods were estimated for some selected early and late flowering genotypes. F85-84l7 had a longer juvenile period, and F85-1226 had both longer juvenile and inductive periods than their respective early flowering isolines and cultivar Essex. cultivar. The method of moving plants from inductive short-days to long-days, which has been used to estimate the length of inductive period, was adapted to estimate the length of the juvenile period as well. Delayed flowering in soybeans appeared to be controlled by two loci, each with two alleles, and delayed flowering appeared to be recessive. Anyone of the genes in the homozygous recessive state delayed flowering. F85-1226 may be segregating for both genes while F85-84l7 appeared to contain only one.
Ph. D.

Includes bibliographical references.
Proteas have been extensively cultivated and are grown as floricultural crop plants in many parts of the world, including South Africa. However, the factors that influence the initiation of flowering in Protea have not been identified. From data gathered by the Protea Atlas Project it is evident that Protea spp. have greatly varying flowering times. Furthermore, flowering times between Protea spp. and their hybrid cultivars are also very different. Towards a better understanding of the factors involved in floral initiation in this cultivated crop, three aspects of flowering were investigated in this study. The carbon input into Protea inflorescence development was determined by measuring respiration rates and weights of developing structures. By manipulating source-sink ratios in plants, the carbon assimilatory capacities to support inflorescences were investigated in three cultivars and one wild-grown species of Protea which develop different sized flowers. As some Proteas flower in response to seasonal change, an orthologue of the floral inducer FLOWERING LOCUS T (FT), ProteaFT (ProFT), was isolated from ‘Carnival’ (P. compacta x P. neriifolia) and its expression pattern followed diurnally and seasonally. Finally, the functions of paralogous genes of Protea LEAFY (ProLFY) from ‘Carnival’ displaying sequence similarity to the meristem identity gene LEAFY from Arabidopsis thaliana, were investigated through heterologous expression studies in A. thaliana.

How come the same species of plants can naturally occur under various conditions in different parts of the world? A plant's ability to adapt in response to a changing climate hinges on the presence of genetic variation in traits, such as flowering phenology. In this study, I examine whether flowering start varies genetically within populations and compare this variation to differences between populations. This study quantifies genetic variation in flowering time in two Italian populations of Arabidopsis thaliana whilst using two Swedish populations as a reference. This was done using a randomized block design where plants were grown in a controlled climate. To characterize and measure flowering phenology, time of bolting and flowering were recorded. The experiment included four populations, a total of 150 maternal lines, and 2980 plants. One-way ANOVAs conducted separately by population indicated significant among-line variation in the two Italian populations. Flowering time differed between the Italian and Swedish populations, but not between the two Italian populations. More data would be needed to draw conclusions about the among-line variation in the Swedish populations. The results indicate that the Italian populations have the potential to respond to selection on flowering time, which is a likely consequence of a changing climate.

A study was conducted at the Maricopa Agricultural Center to determine the influence of planting date on time to flowering of sorghum hybrids. Sorghum was planted on March 19, April 16, May 14, June 18, July 2, July 16, and July 30. A total of 17 sorghum hybrids varying in maturity groups from early to late were planted at each date. The number of days from planting to flowering was greatest at the March 19 planting date and decreased with each planting date thereafter. Growing degree days required to reach flowering likewise decrease as planting was delayed. In order to avoid the heat during pollination in the early part of the summer, early to medium maturity hybrids need to be planted in mid-March at Maricopa. July planting dates resulted in flowering occuring in late August and September.

Since proper timing of flowering is critical for the survival of plant species, plants have evolved a complex genetic network to regulate their transition to flowering in response to endogenous signals and environmental cues. In winter annuals ecotypes of Arabidopsis, a flowering repressor, FLOWERING LOCUS C (FLC), a MADS box transcription factor, is expressed at such level as to inhibit flowering in the first growing season. FLC expression is enhanced by FRIGIDA (FRI) to levels that inhibit the transition to flowering by repressing the expression of the genes often referred to as Floral Pathways Integrators. The main process promoting flowering by the repression of FLC is the vernalization and the duration of cold has been shown to be proportional to the degree of down-regulation of FLC; such repression is maintained for the rest of the plant life even after cold exposure ends, but is restored after meiosis. The repression involves epigenetically stable modifications in FLC chromatin that include a H3 Lys27 trimethylation (H3K27me3) and a H3 Lys9 trimethylation, (Sung et al, 2006). Interestingly, for the light-dependent, autonomous and GA integration and meristematic pathways, comparative genetic approaches show that flowering time genes are conserved between Arabidopsis and a large range of crop species, including legumes and cereals. By contrast, the vernalization pathway seems to be only partially conserved, since FLC and FRI were not characterized in dicots other than Brassicaceae, and recently in sugar beet, vitis and tomato. Wild chicory (Cichorium intybus L.) is a biennial species which requires vernalization to flower. In Italy different types of chicory (the so called Italian red and variegate types) have been selected by farmers as leafy vegetable. These types show quite different classes of precocity in relation to flowering. Given the high heterogeneity, in regard to flowering, manifested by plants belonging to the same variety, the "control" of the switch by agronomical procedures results difficult. The knowledge about the genetic control of flowering time in chicory could be useful to enhance the vegetative phase and then, increase the productivity of the crop. In our study, we are investigating the molecular basis that regulate the switch to flower in chicory by vernalization, to verify whether such mechanism is the same that controls flowering in Arabidopsis, and, finally, to address the diversity of the classes of precocity to one of the cases known for this model plant. We isolated FLC homologues from chicory and characterized their expression patterns in plant tissues and in response to vernalization. We also studied the pattern of cytosine methylation in chicory genomic DNA in response to vernalization. In addition, the vernalization-mediated decrease of FLC transcript was related with changes in SAM morphology. Biological function of CiFLC has been studied by AtFRIflc3 complementation. Up to now our result indicate that arabidopsis and chicory share homologies in regulating FLC expression in the vernalization response, but the absence of complementation of the mutant suggest a disagree in biological function of CiFLC or a loss of function of the transgene in Arabidopsis genetic background. Further analysis will be conducted to define if the machinery in FLC regulation and its biological function is shared between the two species. For this purpose, chicory mutants will be generated. Other aim of this work has been the identification of FLC genomic sequences in chicory. For this purpose, genome walking technique was used. Knowledge of the genomic sequence of CiFLC will allow comparing the regulative regions with those of AtFLC and performing experiments of chromosome hybridization (i.e. FISH). The goal is identify the number of copies of the gene and characterize its position within the chromosomes. With these results we will be able to formulate hypothesis about the evolution of FLC in Cichorium intybus.

Dissertation (PhD(Agric))--University of Stellenbosch, 2006.
ENGLISH ABSTRACT: Advancement of the flowering time of Protea cv. Carnival by approximately three months, without compromising the product quality, was achieved by the application of 6- benzyladenine-containing plant growth regulators to three-flush shoots in autumn. This earlier flowering time coincides favourably with the prime European marketing period (November-January). The percentage three-flush shoots initiating an inflorescence following the brush application of the 6-benzyladenine (BA)-containing regulators, ABG- 3062 (active ingredient: BA 2% w/w) and Accel® (active ingredients: BA 1.8% w/w; gibberellins A4A7 0.18% w/w) on dormant terminal buds, increased with later application dates and flowering percentages as high as 90% was achieved. No inflorescences were initiated on flushes induced by Promalin® (active ingredients: BA 1.8% w/w; gibberellins A4A7 1.8% w/w). Phenological phase progression of green point, flush expansion and inflorescence development of 'Carnival' shoots as induced by BA was calculated to have base temperatures of 8°C, 6°C and 1°C respectively. The days required from application of the BA-containing growth regulator until green point stage increased progressively over the six consecutive treatment dates in autumn (14 March - 22 May 2003). In contrast, the days required to complete inflorescence development decreased with each successive treatment date. The days required between the respective stages were mostly negatively correlated with temperature, except for the phase 'green point to flush expansion', where the relationship was unclear. For three-flush shoots of eight-year old plants, between 13-57, 39-65 and 121-177 days were required to reach green point, to achieve full flush expansion following green point and to complete inflorescence after flush expansion respectively. BA application enhanced budbreak in most dormant shoots, irrespective of plant age, BA concentration, decreasing temperature over time or shoot characteristics. However, twoflush shoots treated in late May had low budbreak and hence low flowering percentages. Shoots varied considerably in their responsiveness to BA treatments. BA application (500mg·L-1) as MaxCelTM (active ingredients: BA 1.9% w/w) to terminal buds alone of mature three-flush shoots from less vigorous growing plants resulted in the highest flowering percentages. Applications were most effective when applied to the terminal bud in the dormant state or up to the ‘green point’ stage. Shoot characteristics such as flush length, leaf area, shoot dry mass, number and proximity of the leaves to the terminal bud were all positively correlated with the propensity of shoots to initiate inflorescence under BA induction. Terminal flush intercalation shoot diameter (>7mm) was identified as the most important variable influencing the likeliness of flowering and can effectively serve as a nondestructive estimation of a shoot's propensity to flower. The presence of developing inflorescences or possible floral inhibiting factors derived from the previous flowering season is suggested to be inhibitory to inflorescence initiation following BA application. Synchronisation of shoot growth by pruning plants in late winter appears to be an essential step to ensure high percentages inflorescence initiation with BA treatment the following autumn. The use of BA as a management tool to control flowering times in Protea for better market opportunities is shown to hold considerable commercial potential.
AFRIKAANSE OPSOMMING: Protea cv. Carnival se blomtyd is met ongeveer drie maande vervroeg sonder om produkkwaliteit prys te gee. Hierdie vervroegde blomtyd wat gunstig saam val met die optimale Europese bemarkingstyd van November-Januarie is bewerkstelling deur die herfstoediening van 6-bensieladenien-bevattende plantgroei-reguleerders op lote bestaande uit drie groeistuwings. Die persentasie lote met drie groeistuwings wat 'n bloeiwyse geïniseer het na 'n kwas-aanwending met die 6-bensieladenien (BA)-bevattende groeireguleerders, ABG-3062 (aktiewe bestandeel: BA 2% w/w) en Accel® (aktiewe bestandele: BA 1.8% w/w; gibberellins A4A7 0.18% w/w), het toegeneem met latere behandelingsdatums en blompersentasies so hoog as 90% is behaal. Geen bloeiwyses is geïnisieer op groeistuwings wat deur Promalin® (aktiewe bestandeel: BA 1.8% w/w; gibberellins A4A7 1.8% w/w) teweeggebring is nie. Basis temperature van 8°C, 6°C en 1°C respektiewelik is bereken vir fenologiese fasevordering vanaf groeireguleerder toediening tot by groenpunt, groeistuwing-voltooing en bloeiwyse-ontwikkeling van 'Carnival' lote soos geïnduseer deur BA. Die dae wat benodig was vanaf toediening van die BA-toediening totdat groenpunt stadium bereik is, het progressief toegeneem oor die ses opeenvolgende herfsbehandelingsdatums (14 Maart-22 Mei 2003). In teenstelling met bostaande, het die vereiste aantal dae om bloeiwyseontwikkeling te voltooi afgeneem met elke opeenvolgende behandelingsdatum. Die aantal dae wat benodig was vir die onderskeie fases was meestal negatief gekorreleer met temperatuur, behalwe vir die fase 'groenpunt tot groeistuwing-voltooing', waar die verhouding onduidelik was. Vir lote van agt-jaar-oue plante met drie groeistuwings was tussen 13-57, 39-65 en 121-177 dae respektiewelik benodig om groenpunt te bereik, volledige groeistuwingverlenging te bewerkstellig en om bloeiwyse-ontwikkeling wat volg na groeistuwing verlenging, te voltooi. BA-toediening het knoprusbreking bevorder in die meeste dormante lote, ongeag plant ouderdom, BA konsentrasie, afname in temperatuur met tyd of loot eienskappe. Lote met twee groeistuwings wat laat in die herfs behandel is, het egter lae rusbreking en dus gevolglik ook lae blompersentasies getoon. Lote varieer aansienlik in hul reaksie op BA behandeling. BA toediening (500mg·L-1) as MaxCelTM (active ingredients: BA 1.9% w/w) op die terminale knop van afgeharde lote met drie groeistuwings en afkomstig van minder groeikragtige plante het tot die hoogste blompersentasies gelei. Die effektiwiteit van die behandeling was die hoogste met toedienings aan dormante terminale knoppe tot en met groenpuntstadium. Loot eienskappe soos groeistuwinglengte, blaaroppervlakte, loot droë massa, asook die aantal en nabyheid van die blare relatief tot die terminal knop was almal positief gekorreleerd met die vermoë van die loot om 'n blom te inisisieer in reaksie op BA induksie. Terminale groeiverstuwing interkalasie-lootdikte (>7mm) is geïdentifiseer as die belangrikste veranderlike wat die vermoë om te kan blom kan beïnvloed en kan gebruik word as 'n nie-destruktiewe voorspeller vir blom-inisiasie. Die teenwoordigheid van ontwikkelende bloeiwyses of potensiële blom-inhiberende faktore aanwesig in die loot na die vorige blomperiode, word moontlik beskou om inhiberend te wees vir BA-geïnduseerde blom-inisiasie. Sinchronisering van lootgroei deur die snoei van plante in laat-winter blyk krities te wees om 'n hoë blompersentasie met BA behandeling te verseker in die daaropvolgende herfs. Die aanwending van BA as 'n bestuurstegniek om die blomtyd van Protea te posisioneer vir beter bemarkingsgeleenthede toon aansienlike kommersiële potensiaal.

Trees dominate terrestrial ecosystems and produce most of the terrestrial biomass, additionally the increasing worldwide demand for timber, pulp and paper and biofuels means trees are of high economical important, consequently the study of trees is important for both ecological and industrial purposes. Dormancy, bud flush and bud set are important traits both ecologically and for breeding purposes, and forest trees display extensive natural variation in these traits for adaptation to the wide range of climates which they inhabit. The candidate genes PtCO2B and PtCO2A are used in an association mapping approach to investigate the natural variation of these traits. The CONSTANS gene is widely known to be involved in photoperiod responsive pathway of flowering in Arabidopsis, and has recently been shown to be involved in flowering and dormancy in Populus. Here the two Populus homologues of CONSTANS are sequenced within a natural population of Populus tremula collected along a latitudinal gradient. The results show that these genes have less nucleotide diversity than other genes studied in the same population, most of the diversity is found in the single intron and that they have an excess of low frequency mutants. These results suggest that the coding region of these genes is conserved and does not tolerate many mutants. Regression analysis showed that none of the polymorphisms found in PtCO2B were associated with any of the phenotypic traits scores within this population. Future phenotyping within this population may find association with other interesting traits involved in the photoperiod pathway.

Environmental signals such as photoperiod and temperature provide plants with seasonal information, allowing them to time flowering to occur in favourable conditions. Most ecotypes of the model plant Arabidopsis thaliana flower earlier in long photoperiods and after prolonged exposure to cold (vernalization). The vernalized state is stable through mitosis, but is not transmitted to progeny, suggesting that the vernalization signal may be transmitted via a modification of DNA such as cytosine methylation. The role of methylation in the vernalization response is investigated in this thesis. ¶ Arabidopsis plants transformed with an antisense construct to the cytosine methyltransferase METI (AMT) showed significant decreases in methylation. AMT plants flowered significantly earlier than unvernalized wildtype plants, and the promotion of flowering correlated with the extent of demethylation. The flowering time of mutants with decreased DNA methylation (ddm1) was promoted only in growth conditions in which wildtype plants showed a vernalization response, suggesting that the early flowering response to demethylation operated specifically through the vernalization pathway. ¶ The AMT construct was crossed into two late flowering mutants that differed in vernalization responsiveness. Demethylation promoted flowering of the vernalization responsive mutant fca, but not of the fe mutant, which has only a slight vernalization response. This supports the hypothesis that demethylation is a step in the vernalization pathway. ¶ The role of gibberellic acid (GA) in the early flowering response to demethylation was investigated by observing the effect of the gai mutation, which disrupts the GA signal transduction pathway, on flowering time in plants with demethylated DNA. The presence of a single gai allele delayed flowering, suggesting that the early flowering response to demethylation requires a functional GA signal transduction pathway, and that demethylation increases GA levels or responses, directly or indirectly. ¶ In most transgenic lines, AMT-mediated demethylation did not fully substitute for vernalization. This indicates that part of the response is not affected by METI-mediated methylation, and may involve a second methyltransferase or a factor other than methylation. A second Arabidopsis methyltransferase, METIIa, was characterized and compared to METI. The two genes are very similar throughout the coding region, and share the location of their eleven introns, indicating that they diverged relatively recently. Both are transcribed in all tissues and at all developmental stages assayed, but the level of expression of METI is significantly higher than that of METIIa. The possible functions of METI, METIIa, and other Arabidopsis cytosine methyltransferase genes recently identified are discussed.

This thesis reports a study of the flowering response of heather, Calluna vulgaris (L.) Hull and of experimental procedures designed to modify the time of onset of that process, with particular reference to year-round production of the flowering plant, in line with recent expansion in the European and British pot plant industries. Microscopic apical examinations were employed throughout to identify and monitor development of floral primordia. Research concentrated on flowering responses to photoperiodic stimuli, provided by various lighting regimes, including fluorescent and tungsten sources, differing in spectral composition and irradiance intensities. Calluna clearly required long day lighting for both floral initiation and development. This response was shown to be influenced by temperature conditions, with higher temperatures promoting flowering. Various changing-temperature regimes were also investigated. Reduced-temperature storage of plants with floral buds was successfully employed as a method of delaying flowering time. Influences of cultivar and seasonal flowering type were also investigated. Results indicated that seasonal flowering sequences were maintained under artificial lighting conditions; so that later flowering types required longer periods of lighting. Evidence suggested a cultivar-dependent sensitivity to irradiance intensity. This information was incorporated in an evaluation of costs incurred during photoperiodic induction, and from this an economic protocol for production of flowering Calluna was compiled; commercial viability being an integral part of the overall study. The minimum plant size capable of floral induction was investigated and related to different modes of propagation; in both macro- and micro-propagated plants flowering occurred soon after root development. Seedlings, however, had to pass through a juvenile phase. The limited micropropagation study revealed that adventitious shoot production involved transitory tissue rejuvenation.

Experimental studies of the flowering of Arabidopsis Thaliana have shown that a large complex gene regulatory network (GRN) is responsible for its regulation. This process has recently been modelled with deterministic differential equations by considering the interactions between gene activators and inhibitors [Valentim et al., 2015, van Mourik et al., 2010]. However, due to the complexity of the models, the properties of the network and the roles of the individual genes cannot be deduced from the numerical solution the published work offers. In this study, deterministic and stochastic dynamic models of Arabidopsis flowering GRN are considered by following the deterministic delayed model introduced in [Valentim et al., 2015]. A stable solution of this model is sought by its linearisation, which contributes to further investigation of the role of the individual genes to the flowering. By decoupling some concentrations, the system has been reduced to emphasise the role played by the transcription factor Suppressor of Overexpression of Constants1 (SOC1) and the important floral meristem identity genes, Leafy (LFY) and Apetala1 (AP1). Two-dimensional motifs, based on the dynamics of LFY and AP1, are obtained from the reduced network and parameter ranges ensuring flowering are determined. Their stability analysis shows that LFY and AP1 are regulating each other for flowering, matching experimental findings (see e.g. [Bl ́azquez et al., 2001, Welch et al., 2004, Yeap et al., 2014]). Moreover, the role of noise is studied by introducing and investigating two types of stochastic elements into the motifs. New suffient conditions of mean square stability and their domain are obtained analytically for the stochastic models using Lyapunov stability theory. Numerical solutions are obtained by using Euler-Maruyama method and Ito stochastic formula. We demonstrate that the stochastic motifs of Arabidopsis flowering time can capture the essential behaviour of the full system and that stochastic effects can change the behaviour of the stability region through a stability switch. Furthermore, the problem of designing an observer and a controller, in which FT is seen as a control input, is considered in the objective of ensuring flowering conditions are met. This study thus contributes to a better understanding of the role of LFY and AP1 in Arabidopsis flowering.

In both plants and animals Polycomb group (PcG) genes act to maintain silencing of key developmental genes. A number of PcG genes have been identified in Arabidopsis through independent genetic screens. These can be placed in three groups based upon strong homology with the Drosophila proteins E(z), ESC and SU(Z)12. Arabidopsis contains multiple homologues of E(z) and these have evolved to act in different pathways (CURLY LEAF represses flowering in the immature plant; MEDEA prevents certain aspects of seed development in the absence of fertilisation; and CURLY LEAF LIKE has recently been shown to be partially redundant to CLF). Despite the high level of conservation between CLF and MEA proteins, I have shown that they are not equivalent. MEA is unable to rescue a clf- when expressed under either the CLF endogenous promoter or the constitutative 35S promoter. In Drosophila it has been shown that E(Z) acts in multimeric protein complexes with the PcG proteins ESC and SU(Z)12. Through yeast-two hybrid assays I have shown that CLF physically interacts with both the SU(Z)12 homologue EMF2 and the ESC homologue FIE, providing evidence of a similar complex acting to repress flowering in the immature plant. I have mapped the domains to which these interactions mediate. Of particular interest is the interaction between EMF2 and CLF; this region maps to the VEFS box of EMF2 and the C5 region of CLF. Embryos carrying a maternal inherited fie allele abort during deed development, making it impossible to observe the role of FIE post seed development. I have created a transgenic steroid-inducible FIE line, which I have used to rescue fie- embryos. The resulting plants show severe developmental abnormalities, with highly disorganised organ growth.

The recessive moe leaf (moe) mutation confers a similar phenotype to clf mutations. Molecular and genetic studies indicated that like CLF, MOE activity is required to repress floral homeotic gene expression suggesting that the wild-type MOE gene might define an additional Pc-G protein. This was confirmed by the isolation of MOE. Thus mapping of MOE showed that it is located to the region of a recently isolated Arabidopsis Pc-G member, the EMBRYONIC FLOWER2 (EMF2) gene which play an important role in repressing floral genes during vegetative development. Subsequent genetic analysis indicated that moe is allelic to emf2 mutations and cloning of EMF2 locus from moe mutants showed that the moe allele harbours a small deletion in the EMF2 sequence. It appeared that moe represents a novel weak allele of EMF2 and its phenotype was unlike that of other emf2 alleles described, and informative as to EMF2 function. In particular, genetic analysis using moe and weak clf alleles suggested that EMF2 has a close functional relationship with CLF. Reverse genetic approaches were used to determine the function of an Arabidopsis CLF homologue called CURLY LEAF LIFE-1 (CLK1). CLF and CLK1 show extensive sequence similarity suggesting that they have a common evolutionary origin. Investigation of mRNA localisation by in situ hybridisation indicated that CLF and CLK1 RNA expression patterns are very similar. In addition CLF and CLK1 proteins show common interactions in yeast two-hybrid assay. Together these findings suggested that CLF and CLK1 may show functional redundancy. Characterisation of transgenic lines expressing a dominant negative CLK1 construct, and of a line carrying a T-DNA insert in the CLK1 5’UTR, both provided strong support for this hypothesis. Thus reduced CLK1 activity had little or no effect in wild-type background, but strongly enhanced the clf phenotype.

Several reproductive processes of tetraploid Grindelia camporum were investigated. This plant is a potential resin crop for the southwestern United States. Field observations of 100 flower heads from unopened buds through 100% achene dispersal were made. It was found that individual flower heads are available for pollination for approximately 5 days but all disc florets are open for only 1 day. On average, achenes mature in 22 days and are dispersed 53 days after flowering. Fourteen-hundred hand-pollinations were also made on plants from 6 wild populations of G. camporum grown in a greenhouse and shade house. Estimates of fertility and crossability of populations were made based on achene number and achene weight data from these crosses. All populations studied were interfertile and no evidence of outbreeding depression in between -population crosses was found. It is shown that tetraploid G. camporum is self-incompatible and requires manipulation for achene set.

Lotus corniculatus L. (Legtuninosae), is a perennial herb common throughout Britain. Its main pollinators are bumblebees (Bombus spp., Apidae: Hymenoptera). This is a study of the ecological factors which are important to flowering and fruiting in the species, and some of their evolutionary implications. The work was carried out at Wytham Estate, Oxfordshire, U.K., mainly in an ex-arable field (Upper Seeds) and a more established grassland (Lower Seeds Reserve). The literature on self-incompatibility in L. corniculatus is reviewed; there are conflicting reports, but wild material is fundamentally self-incompatible. Plants in Upper Seeds are larger than in Lower Seeds Reserve. Comparative data on soil nutrients in the two sites suggests that the cause is the persistence of phosphorus from inorganic fertiliser. There is a positive, linear relationship between plant size, flower production and fruit production. The species regulates investment in flowers mainly at the level of the whole inflorescence, rather than altering number of flowers per inflorescence. Within individuals, there are no consistent trade-offs between number of fruit per infructescence, numbers of seeds per fruit and seed weight. Weather patterns only partially explain the flowering phenology of L. corniculatus. Timing of first flowering and peak flowering are correlated but are variable between individuals, and between years for the same individuals. They are not correlated with flowering synchrony. An individual's flowering pattern does not consistently affect fruit-set; the overriding determinant of fruit production is plant size. Selection is therefore unlikely to be acting on flowering time in this species. The production of large numbers of self-incompatible flowers does not seem to reduce fruit-set; pollinators do not visit enough flowers per foraging trip (perhaps because nectar production is low) for geitonogamy to become a problem. Seed predation by larvae of a chalcid wasp, a weevil and a moth differs between individual plants, but not consistently so between years. Seed predation is not consistently correlated with plant size, mean flowers per inflorescence, number of seeds per fruit or seed size. There is no evidence for selection acting on these traits through seed predation. Partially predated seeds are often viable, which may have implications for seedling demography. Seed predation and flowering phenology are not defmitively linked, strengthening the argument that flowering time is not adaptive in this species.