Academic literature on the topic 'Photo-acclimation'

Long-term acclimation of photo- and pigment-chemistry was investigated in a naturally-regenerating stand of Acacia melanoxylon R.Br. ex Ait. A pronounced decrease in photochemical efficiency of A. melanoxylon saplings was observed between autumn and winter in both thinned and unthinned treatments, but the decrease was more severe in the thinned treatment. Associated pigment changes in the unthinned treatment included a decrease in total chlorophyll content and a rise in chlorophyll a : b. Similar acclimation occurred in the thinned treatment with additional increase in zeaxanthin per unit chlorophyll observed. Saplings in the thinned treatment were exposed to lower minimum temperatures, more hours of frost and higher light intensities in the mid- to lower-crown. Growth chamber studies of the short-term acclimation of photo- and pigment-chemistry were conducted in a low / high light and cold / warm temperature factorial experiment. Photochemical efficiency and quantum yield adjusted within one day and then remained constant for 10 d in response to the imposed treatments. Chlorophyll concentration had decreased in all treatments by day 2 in the growth chambers, and subsequently increased in warm, but not in cold, treatments, irrespective of light level by day 10 in the growth chambers. The concentration of lutein-5,6-epoxide decreased in response to the cold-high light treatment and increased in response to other treatments by day 10 in the growth chambers, consistent with a function in sustained photoprotection in leaves of shade-adapted species. Our experiments indicated that A. melanoxylon is susceptible to cold-induced photoinhibition under cool temperatures (2–8°C) and moderate light intensities (450 μmol m–2 s–1).

Abstract. An established one-dimensional Shelf Sea Physics and Primary Production (S2P3) model has been developed into three different new models: S2P3-NPZ which includes a nutrient–phytoplankton–zooplankton (NPZ) framework, where the grazing rate is no longer fixed but instead varies over time depending on different functions chosen to represent the predator–prey relationship between zooplankton and phytoplankton; S2P3-Photoacclim which includes a representation of the process of photo-acclimation and flexible stoichiometry in phytoplankton; and S2P3 v8.0 which combines the NPZ framework and the variable stoichiometry of phytoplankton at the same time. These model formulations are compared to buoy and conductivity–temperature–depth (CTD) observations, as well as zooplankton biomass and in situ phytoplankton physiological parameters obtained in the central Celtic Sea (CCS). Models were calibrated by comparison to observations of the timing and magnitude of the spring phytoplankton bloom, magnitude of the spring zooplankton bloom, and phytoplankton physiological parameters obtained throughout the water column. A sensitivity study was also performed for each model to understand the effects of individual parameters on model dynamics. Results demonstrate that better agreement with biological observations can be obtained through the addition of representations of photo-acclimation, flexible stoichiometry, and grazing provided these can be adequately constrained.

Freezing is a major environmental stress during an annual cycle of overwintering, temperate-zone perennials. The timing and extent of seasonal cold acclimation (development of freezing tolerance in the fall) and deacclimation (loss of acquired freezing tolerance in response to warm temperatures) are of critical importance for winter survival, particularly in view of the climate change, i.e., unpredictable extreme weather occurrences. For example, plants may acclimate inadequately if exposed to a milder fall climate and may be damaged by sudden frosts. Alternatively, they may deacclimate prematurely as a result of unseasonable, midwinter warm spells and be injured by the cold that follows. Efficient cold acclimation ability, high deacclimation resistance, and efficient reacclimation capacity are, therefore, important components of winter survival in overwintering perennials. These components should be evaluated separately for a successful breeding program focused on improving winter-hardiness. Another layer of complexity that should be carefully considered is that endodormant status (shallow versus deep) of the reproductive/vegetative apices can significantly impact these components of winter-hardiness. Winter survival, especially by woody evergreens, requires tolerance of light stress, which can result in photo-oxidative damage at cold temperatures when biochemistry of photosynthesis is somewhat compromised but light harvesting is unaffected. Accumulation of Elips (early light-induced proteins) in overwintering evergreens during winter represents a relatively novel strategy to cope with such light stress, and investigations on the precise cellular mechanism and genetic control of this strategy deserve research in the future. Investigations into the mechanisms for cold acclimation use laboratory-based, artificial acclimation protocols that often do not closely approximate conditions that plants are typically exposed to in nature. To draw meaningful conclusions about the biology of cold acclimation and ultimately improve freeze resistance under field conditions, one should also include in cold acclimation regimens parameters such as exposure to subfreezing temperatures and realistic diurnal temperature fluctuations and light levels to simulate natural conditions. One of the main objectives of this article is to highlight two areas of research that we believe are important in the context of plant cold-hardiness but, so far, have not received much attention. These are: 1) to understand the biology of deacclimation resistance and reacclimation capacity, two important components of freeze-stress resistance (winter-hardiness) in woody perennials; and 2) to investigate the cellular basis for various strategies used by broad-leaved evergreens for photoprotection during winter. Our emphasis, in this context, is on a family of proteins, called Elips. The second objective of this article is to draw attention of the cold-hardiness research community to the importance of using realistic cold acclimation protocols in controlled environments that will approximate natural/field conditions to be better able to draw meaningful conclusions about the biology of cold acclimation and ultimately improve freeze resistance. Results from our work with Rhododendron (deciduous azaleas and broad-leaved evergreens), blueberry, and that of other researchers are discussed to support these objectives.

Philosophiae Doctor - PhD
Gethyllis multifolia L. Bolus and G. villosa Thunb. are winter-growing, summerblooming,deciduous and bulbous geophytes that grow naturally in the semi-arid succulent Karoo biome of South Africa. Both species grow under full sun conditions and have four distinctive growth phases: a winter (cold and wet) growing phase, leaf senescence phase towards spring, flowering phase during the hot and dry summer months, and fruit and leaf formation phase in autumn. The medicinal uses of this genus (including G. multifolia “Kukumakranka” and G.villosa “hairy kukumakranka”) range from cures for colic, digestive disturbances,teething problems, fatigue, boils, bruises and insect bites, to being used as an aphrodisiac. Gethyllis multifolia is threatened in its natural habitat and is listed in the ‘Vulnerable’ category of the ‘Red Data List of Southern African Plants’ and the ‘IUCN-World Conservation Union List of Plants’. The literature indicate that the habitats of both species are being exposed to drier conditions and is further threatened by the encroachment of invasive indigenous plant species. It is not known to which extent these factors may pose a threat to the existence of both species. The first objective of this investigation was to determine the costs of vegetative and reproductive growth during the seasonal life cycle of the plant, using carbon(C) and nitrogen (N) as a physiological currency. The second objective was to elucidate a functional basis to explain the difference in the conservation status of both species in their natural habitat. Both species were subjected to drought and shading as environmental stresses and the plant physiological performance was investigated via photosynthetic gas exchange. The third objective of the study was to evaluate the antioxidant content (total polyphenol, flavonol/flavone and flavanone content) and antioxidant capacity [ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC) and 2,2'-azino-di-3-ethylbenzthiazoline sulphonate (ABTS) radical cation scavenging ability] of natural populations and plant samples that were exposed to photo-and-drought environmental stresses. This study was done to elucidate the antioxidant profile of plant parts of natural populations as well as providing farmers, traditional healers and pharmaceutical companies with cultivation environmental conditions to enhance the antioxidant properties of the species. This investigation also attempted to isolate and characterize, by means of thin-layer chromatography (TLC) and column chromatography (CC), natural compounds from both species to lend support to the purported antioxidant benefit of both species and to further lend support to claims made by traditional healers of the medicinal potential of the genus. This study, however, did not engage in any in vivo studies or human trials to support published literature of the medicinal benefits of the genus.

The ecology and photo-acclimation mechanisms of microalgae belonging to the class Raphidophyceae were studied, both in nature and in culture. Particularly the work was focused on: Fibrocapsa japonica atypical occurrence offshore, in a cyclonic eddy in the eastern Alboran Sea (Western Mediterranean Sea), and Heterosigma akashiwo photosynthetic parameter (alpha, beta and Pmax) co-variation during experiments under sinusoidal and continuous light regime, and nitrogen starvation, which were conducted at the Laboratoire d’Oceanographie, Observatoire Oceanologique, Villefranche-sur-mer, Unviersitè Pierre et Marie Curie, CNRS, France.

This thesis is constituted of an introductive section given detailed information about the metabolic versatility of purple non sulfur bacteria. An exhaustive description of the photo-fermentation process in purple non sulfur bacteria is also offered, with particular consideration to the conditions needed to produce hydrogen. The acclimation (chromo-acclimation) to high light intensities in purple non sulfur bacteria is detailed described, and the role of photo-pigments into this process is highly considered. Moreover, a short description of all ways to dissipate the excess of energy by photosynthetic organisms, is included in this introduction. The use of different techniques to understand the molecular/ energetic status of the photosynthetic unit is presented, with particular attention to Pulse- Amplitude- modulation (PAM) fluorescence and Saturation Pulse Method of Quenching Analysis. In this section, a general view regarding the inhomogeneity problems of light distribution during the photo- fermentation process using purple non sulfur bacteria is offered. Furthermore, short statements about one topic with a few references in literature is described, i.e. production of hydrogen as a way to discard the excess of reducing power generated as a result of high light intensities exposure. The main aim of this thesis was to study the behavior of the purple non sulfur bacterium Rhodopseudomonas palustris strain 42OL to different culturing conditions illuminated at high light intensities, with particular interest to the production of hydrogen as a way to dispose the excess of reductants and as a mechanism to preserve a well physiological status. Besides, the acclimation to high light intensities in this strain was also one of the main objectives to be studied, particularly the trend of photo- pigments.

Gethyllis multifolia L. Bolus and G. villosa Thunb. are winter-growing, summerblooming, deciduous and bulbous geophytes that grow naturally in the semi-arid succulent Karoo biome of South Africa. Both species grow under full sun conditions and have four distinctive growth phases: a winter (cold and wet) growing phase, leaf senescence phase towards spring, flowering phase during the hot and dry summer months, and fruit and leaf formation phase in autumn. The medicinal uses of this genus (including G. multifolia “Kukumakranka” and G. villosa “hairy kukumakranka”) range from cures for colic, digestive disturbances, teething problems, fatigue, boils, bruises and insect bites, to being used as an aphrodisiac. Gethyllis multifolia is threatened in its natural habitat and is listed in the ‘Vulnerable’ category of the ‘Red Data List of Southern African Plants’ and the ‘IUCN-World Conservation Union List of Plants’. The literature indicate that the habitats of both species are being exposed to drier conditions and is further threatened by the encroachment of invasive indigenous plant species. It is not known to which extent these factors may pose a threat to the existence of both species. The first objective of this investigation was to determine the costs of vegetative and reproductive growth during the seasonal life cycle of the plant, using carbon (C) and nitrogen (N) as a physiological currency. The second objective was to elucidate a functional basis to explain the difference in the conservation status of both species in their natural habitat. Both species were subjected to drought and shading as environmental stresses and the plant physiological performance was investigated via photosynthetic gas exchange. The third objective of the study was to evaluate the antioxidant content (total polyphenol, flavonol/flavone and flavanone content) and antioxidant capacity [ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC) and 2,2'-azino-di-3- ethylbenzthiazoline sulphonate (ABTS) radical cation scavenging ability] of natural populations and plant samples that were exposed to photo- and -drought environmental stresses. This study was done to elucidate the antioxidant profile of plant parts of natural populations as well as providing farmers, traditional healers and pharmaceutical companies with cultivation environmental conditions to enhance the antioxidant properties of the species. This investigation also attempted to isolate and characterize, by means of thin-layer chromatography (TLC) and column chromatography (CC), natural compounds from both species to lend support to the purported antioxidant benefit of both species and to further lend support to claims made by traditional healers of the medicinal potential of the genus. This study, however, did not engage in any in vivo studies or human trials to support published literature of the medicinal benefits of the genus. The photosynthetic adaptation studies indicated that G. villosa had a better photosynthetic performance than G. multifolia during both drought and low light conditions because of the inability of G. multifolia to adapt to a wider range of environmental extremes. The C and N cost of growth and reproduction studies revealed that G. villosa had a more efficient resource utilisation strategy for both growth and reproduction. These physiological responses suggest that G. villosa, in general, has a more efficient survival strategy and that G. multifolia will struggle to adapt to drier environmental conditions, as well as growing in the shade of encroaching invasive plant species. To conclude, this could be a contributing factor as to why G. multifolia is threatened in its natural habitat and G. villosa not. The antioxidant content-and -capacity study on natural populations of both species revealed the highest total polyphenol content, FRAP and ORAC values for the flowers and fruits of G. multifolia and G. villosa compared to other plant parts. These values were found to be in line with and in some cases higher than most commercial fruits and vegetables. The antioxidant activity during drought and photo-stress of the leaves, bulbs and roots was found to be highest in the roots of both species during drought stress. Gethyllis multifolia, in general, exhibited higher total polyphenol content than G. villosa, with the highest content measured during drought stress in the roots of G. multifolia. Phytochemical investigation of the leaves, bulbs and roots of G. multifolia and G. villosa revealed the presence of tannins, flavonoids, phenolics, saponins, glycosides as well as essential oils, while alkaloids were absent. The chromatographic profiles of the leaves, bulbs and roots of both species further indicated that the roots of G. multifolia contained the highest concentration of natural products, compared to G. villosa and other plant parts. Further in-depth studies on the roots of G. multifolia led to the isolation and characterization of three known flavonoids, of which one was also isolated as its endogenously acetylated derivative. In contrast to the fact that both species had a high polyphenol content and exhibited high antioxidant activity, the isolated compounds in this study revealed very low antioxidant activity. However, the literature revealed that some of these isolated compounds exhibit antifungal, antibacterial, antiangiogenic and anticarcinogenic properties in vitro, which could be ascribed to the medicinal applications of plant parts of certain species belonging to this genus. Furthermore, this study suggests that further chemistry and pharmaceutical research on the genus, Gethyllis, in specific the flowers and fruit of these two species, be pursued.
Philosophiae Doctor - PhD