Orientador: Luiz Fernando Rolim de Almeida / Resumo: Orquídeas epífitas estão expostas a diferentes microclimas, que são caracterizados pela alta irradiância imposta ao dossel e baixa irradiância em plantas situadas no sub-bosque. Além disso, este grupo de plantas frequentemente lida com a restrição hídrica. Na produção comercial, o estabelecimento de orquídeas é em quase sua totalidade limitada pela distribuição e intensidade destes mesmos fatores disponibilizados em casas de vegetação. Gomesa flexuosa Sims e Oncidium sphacelatum Lindley pertencem à subtribo Oncidiinae, e quando hibridizadas dão origem a O. ‘Aloha’ (uma orquídea CAM facultativa e importante híbrida comercial). O objetivo deste estudo foi elucidar a performance fotossintética e as estratégias de balanço hídrico de G. flexuosa e O. sphacelatum sob condições de estresse hídrico e luminoso, focando tanto nas diferenças interespecíficas como nas funções dos diferentes órgãos em um mesmo indivíduo. Para isso, analisamos trocas gasosas, fluorescência da clorofila a, quantificação de lipoperóxidos, discriminação isotópica, acidez titulável, conteúdo relativo de água e potencial hídrico em tecidos foliares, de pseudobulbos e raízes, em diferentes tratamentos envolvendo restrição hídrica e variação luminosa. Depois de restrição hídrica por 60 dias, G. flexuosa apresentou conversão de metabolismo C3 para CAM, o que deu subsídios para uma melhor performance das trocas gasosas, fluorescência da clorofila a, mecanismo de fotoproteção e relações hídricas. Quando submetida a ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Epiphyte orchids are exposed to different microclimates, which are characterized by high irradiance imposed on the canopy and low irradiance in plants located on the understory. In addition, this group of plants frequently deals with water restriction. In commercial production, the distribution and intensity of these same factors inside the greenhouses also limit the orchids establishment. Gomesa flexuosa Sims and Oncidium sphacelatum Lindley are Oncidiinae species and when hybridized, it gave origin to O. ‘Aloha’ (a facultative CAM orchid and na important commercial hybrid). The aim of this study was to elucidate the photosynthetic performance and the water balance strategies of G. flexuosa and O. sphacelatum under water and light stress conditions, focusing on an interspecific diferences as well as on different organs functions in the same individual. For that, we analyzed the gas exchange, chlorophyll a fluorescence, lipoperoxides quantification, isotopic discrimination, titratable acidity, water relative content and water potential of leaf, pseudobulb and root tissues in different treatments involving water restriction and light variation. After 60 days of water restriction, G. flexuosa converted the photosynthetic metabolism from C3 to CAM, which provided a better performance on gas exchanges, chlorophyll a fluorescence, photoprotection mechanism and water relations. When G. flexuosa was submitted to two events of water restriction, it showed a capacity to store informat... (Complete abstract click electronic access below) / Doutor

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Anticiper les impacts des changements climatiques sur les écosystèmes terrestres, notamment sur le cycle du carbone, nécessite la compréhension et la quantification du fonctionnement photosynthétique des végétaux et leurs réponses aux contraintes abiotiques. Suivre l’évolution des propriétés spectrales des couverts végétaux par la télédétection permet d’avoir accès à leur fonctionnement à des échelles spatiales et temporelles variées. Plusieurs indicateurs optiques ont été développés afin d’accéder à la structure, la biochimie et le fonctionnement écophysiologique des végétaux. Le PRI (photochemical reflectance index), déterminé à partir de la réflectance mesurée dans des bandes étroites à 531 nm et 570 nm, est un proxy de l’efficacité de la plante à utiliser la lumière (LUE, light use efficiency) et plus particulièrement du cycle des xanthophylles, utilisé par la plante pour dissiper l’énergie lumineuse excédentaire sous forme de chaleur. Cependant son usage à l’échelle du couvert végétal, ou à plus larges échelles temporelles et spatiales, entraine l’implication de nombreuses sources de variabilités qui masquent la sensibilité du PRI au fonctionnement photosynthétique, particulièrement les variations biochimiques et phénologiques. L’objectif de ce travail est de mieux comprendre les facteurs qui jouent sur la variabilité du PRI à l’échelle de la feuille et du couvert, afin de caractériser ses réponses aux variations abiotiques de l’environnement et de démêler la composante phénologique de la composante physiologique du PRI. Des études ont été menées en conditions contrôlées, semi-naturelles et naturelles, sur des jeunes arbres et en forêt adulte, soumis à différentes contraintes abiotiques. L’analyse des courbes de réponse du PRI aux variations de lumière incidente utilisée pour la photosynthèse (PAR, photosynthetically active radiation) permet d’isoler 3 paramètres. Le PARsat, la valeur de PAR pour laquelle le PRI sature, le PRI₀, la valeur du PRI à une intensité lumineuse faible (mesurée) ou nulle (estimée) et le ∆PRI, l’amplitude de variation entre le PRI₀ et la valeur de PRI maximum. En période de végétation, la variabilité du PARsat est principalement contrôlée par la disponibilité en eau pour la plante. La variabilité du PARsat est aussi impactée par la concentration d’ozone atmosphérique. En période de débourrement et de sénescence, la variabilité du contenu en chlorophylle régit la valeur du PARsat. Ce paramètre explique la variabilité physiologique du PRI et varie en fonction du facteur limitant la photosynthèse. La variabilité du PRI₀ a été expliquée par la variabilité du contenu biochimique des feuilles en réponse au cycle saisonnier de la chlorophylle et à sa variabilité en conditions de stress. A l’échelle de la canopée, la variabilité de la structure du couvert s’ajoute à la variabilité biochimique du PRI₀. Le PRI₀, en temps que composante phénologique de la variabilité du PRI, peut être utilisé pour corriger le PRI afin de lui soustraire la variabilité structurale et obtenir un PRIc fortement corrélé à la LUE. A l’échelle de la canopée, il a été montré que le PRI est principalement représentatif de la strate supérieure du couvert. Le ∆PRI n’a montré aucune variation intra et inter-journalière, suggérant que le PRI répond non pas au contenu en xanthophylle des plantes, mais à un ratio maintenu constant. Ces résultats mettent en évidence l’importance d’isoler les différentes sources de variabilité du PRI avant de l’utiliser comme proxy du fonctionnement photosynthétique des écosystèmes terrestres. / Anticipating impacts of climate change on terrestrial ecosystems, particularly on the carbon cycle, requires the understanding and the quantification of the plant photosynthetic functioning and of their responses to abiotic factors. Tracking variations of spectral properties of plants using remote sensing allows the access of plant functioning at various spatial and temporal scales. Several optical indices have been developed to assess plant canopy structure, biochemistry and ecophysiological functioning. The PRI (photochemical reflectance index), determined from reflectances measured in narrow bands at 531 nm and 570 nm, may be used as a proxy of light use efficiency (LUE) at leaf and canopy scales, and more particularly of the xanthophyll cycle used by plants to dissipate the excess light energy as heat. However the use of PRI at the canopy scale and at large temporal and spatial scales faces several difficulties related to the involvement of different sources of variability that blur PRI sensitivity to photosynthetic functioning. These sources of PRI variability are particularly linked to spatial and temporal variations of biochemical and phenological canopy properties. The aim of these studies is to better understand the factors affecting PRI variability at leaf and canopy scales, to assess the strength of the relationships between PRI and vegetation responses to environmental abiotic constraints and disentangling the phenological component from the physiological component of PRI. Studies were conducted under controlled, semi-natural and natural conditions, on young trees and a mature deciduous forest subjected to various abiotic constraints. The analysis of PRI responses to the variations of photosynthetically active radiation (PAR) allowed isolating three parameters. The PARsat, the PAR value at the PRI saturation; the PRI₀, the value of PRI at dim light (measured) or in darkness (estimated) and the ΔPRI, the range of PRI variations between the PRI₀ and the maximum value of PRI. During the leaf growing season, PARsat variability is mainly controlled by the availability of water content for the plant. The PARsat variability is also impacted by the atmospheric ozone concentration. During the phenological phases of budburst and the senescence, the variability of the leaf chlorophyll content governs PARsat values. This parameter describes the physiological variability of PRI and varies depending on the limiting factor for photosynthesis. The PRI₀ variability has been explained by the dynamic of the biochemical content of the leaves linked to the seasonal variations of chlorophyll content and to abiotic stress conditions. At canopy scale, the structural variability is added to the biochemical variability of PRI₀. The PRI₀, as the phenological component of PRI variability, can be used to correct PRI, removing its structural variability to obtain a PRIc strongly correlated to LUE. At canopy scale, it was shown that the PRI is mostly representative of the upper layer of the canopy. The ΔPRI showed no variation within and between days, suggesting that the PRI does not respond to the plant xanthophyll content but rather to a ratio maintained constant. These results highlight the importance of isolating the different sources of PRI variability before its use as a proxy of the photosynthetic functioning of terrestrial ecosystems.

Tocopherols, collectively known as vitamin E, are lipophilic antioxidants, which are synthesized only by photosynthetic organisms. Due to their enormous potential to protect cells from oxidative damage, tocopherols are used e.g. as nutraceuticals and additives in pharmaceuticals. The most biologically active form of vitamin E is α-tocopherol. Most tocopherols are currently produced via chemical synthesis. Nevertheless, this always results in a racemic mixture of different and less effective stereoisomers because the natural isomer has the highest biological activity. Therefore, tocopherols synthesized in natural sources are preferred for medical purposes. The annual sunflower (Helianthus annuus L.) is a well-known source for α-tocopherol. Within the presented work, sunflower callus and suspension cultures were established growing under photomixotrophic conditions to enhance α-tocopherol yield. The most efficient callus induction was achieved with sunflower stems cultivated on solid Murashige and Skoog medium supplemented with 30 g l-1 sucrose, 0.5 mg l-1 of the auxin 1-naphthalene acetic acid and 0.5 mg l-1 of the cytokinin 6-benzylaminopurine. Photomixotrophic sunflower suspension cultures were induced by transferring previously established callus into liquid medium. The effects of light intensity, sugar concentration and culture age on growth rate and α-tocopherol synthesis rate were characterized. A considerable increase (max. 230 %) of α-tocopherol production in the cells was obtained within the photomixotrophic cell culture compared to a heterotrophic cell culture. These results will be useful for improving α-tocopherol yields of plant in vitro cultures.

<p>Climate change and the energy crisis are substantial challenges facing the human species, and they are projected to threaten life on our planet. For millions of years, the sun has been the main source of energy for life on Earth; this inspires ongoing research efforts focusing on a “sunlight to fuel” energy solution. Photosynthesis is nature’s tool to derive energy from the sun. Hence, scientists focus on the biochemistry of this phenomenon to employ photosynthesis in a man-made device. Such a device is able to convert solar energy to chemical energy through a light-driven cycle of the chemical reactions which produce hydrogen gas, later used as fuel. This process, often called “artificial photosynthesis,” needs efficient catalysts which can be incorporated into a molecular assembly and other microscopic structures or immobilized on an electrode surface. </p><p>Additionally, evolution, in the course of billions of years, chose manganese as an abundant and effective metal to facilitate the process of photosynthesis. These manganese atoms formed a cluster and an optimized ligand field to maximize efficiency. The photochemistry and photo-physics process behind photosynthesis is yet to be fully understood and implemented in a man-made apparatus with comparable efficiency and durability. </p><p>Photosynthesis requires a source of electrons. Water is an abundant molecule on earth that can provide the electrons needed for the photosynthesis. Although water is ubiquitous, it is one of the most stable molecules; hence, splitting it demands a well-designed system with strong oxidizing capability. Because a single atom of oxygen is highly reactive, there should be at least four oxidation states in the system to remove four electrons and release molecular oxygen: O2. The O-O bond formation is one of the most important steps in photosynthesis to fully understand. Lacking a thorough knowledge of this step prevents design and fabrication of robust and active water oxidizing catalysts. To fully understand O-O formation, one should perform a comprehensive study of each of the intermediates of the system. In other words, we need an understanding of the structure and electronic configuration of the system (natural or artificial) from the moment that a water molecule attaches to the catalyst (usually a metal core, central in the complex), until the moment that oxygen released as an O2 molecule. </p><p>There are multiple possible mechanisms to explain O-O formation. Two mechanisms that were extensively studied in this thesis are water nucleophilic attack and radical coupling. The prevailing view about oxygen formation in the catalysts that we study here explains the O-O bond formation by nucleophilic attack of a water molecule to a highly oxidized ruthenium (RuV=O) species. In this hypothesis, all polypyridine ligands that are coordinated to ruthenium remain neutral during the water oxidation process, while the formation of RuV=O (the key intermediate) would require a relatively high free energy (about 1.8 to 2 eV); use of computational (numerical) calculations determine this to be thermodynamically inaccessible. Furthermore, the failure of spectroscopic techniques to confirm the presence of RuV=O calls the validity of this model into question.)</p><p>Alternatively, radical coupling hypothesis considers another pathway to oxygen bond formation. Here, one of the nitrogen atoms coordinated to ruthenium in polypyridine plays a crucial role. We hypothesize that after formation of RuIV=O (which is spectroscopically observed), one nitrogen decoordinates from the metallic core (ruthenium) and oxidizes to form Ru-ON species. This N-oxide ligand can be further oxidized to form a ligand cation radical. It has been shown that [ligand-NO]+• can have almost no energy barrier for O-O bond formation via spin alignment. The study of the role of N-oxide is one of the main focuses of this work. Since this hypothesis does not require RuV=O nor water nucleophilic attack, it explains the process of water oxidation and opens further avenues for the design of future catalysts.</p><p>To confirm our hypothesis, I employed several spectroscopic methods and computational calculations. This new pathway predicts new intermediates exclusive to this model. Our objective is to prove their presence by in situ spectroscopy and test the possibility of formation of each intermediate computationally, to see if their formation is thermodynamically feasible. </p><div><br></div>

Photosynthesis and primary production were estimated in fishpond phytoplankton during period 2008-2010 in Třeboň fishpond region, Czech Republic. Photosynthesis was measured by the oxygen method in computer-assisted light pipetting system Illuminova. Altogether 64 samples of fishpond phytoplankton and 11 cyanobacterial cultures were analysed. Cyanobacteria and chlorococcal algae formed the most important part of phytoplankton biomass and their photosynthesis-irradiance (P-I) curves showed shade-adapted type of P-I curves with the high photosynthetic efficiency. No significant differences in the main parameters of P-I curves were obtained between different types of phytoplankton (chlorococcal-dominated, cyanobacteria- dominated). The results are consistent with the high turbid conditions in eutrophic or hypetrophic fishponds. On the contrary photosynthesis in cyanobacterial cultures differs from "wild" phytoplankton and therefore they can not be taken in primary production models. Primary production was estimated according Talling's model (1957), based on daily measurement of radiation, extinction coefficient of water and seasonal courses of chlorophyll concentration. Photosynthetic capacity and onset of light saturation determined in P-I curves were used as physiological parameters of Talling's model. The...

<p>Tropical ecosystems play a key role in regulating the global climate and the carbon cycle thanks to the large amounts of water and carbon exchanged with the atmosphere. These biogeochemical fluxes are largely the result of high photosynthetic rates. Photosynthetic activity is highly dependent on climate and vegetation, and therefore can be easily modified along with changes in those two factors. A better understanding of what drives or alters photosynthetic activity in the tropics will lead to more accurate predictions of climate and subsequent effects on ecosystems. The seasonal pattern of photosynthetic activity is one of the main uncertainties that we still have about tropical ecosystems. However, this seasonality of tropical vegetation and its relationship to climate change and land cover is key to understanding how these ecosystems could be affected and have an effect on climate.</p><p>In this dissertation, I present three projects to improve our understanding about tropical ecosystems and how their photosynthetic activity is affected by climate and land cover change. The lack of field-based data has been one of the main limiting factors in our study of tropical ecosystems. Therefore, in these projects I extensively use remote sensing-derived data to analyze large scale and long term patterns. In the first study, I looked at the seasonal relationship between photosynthetic activity and climate, and how model simulations represent it. Vegetation in most of the tropics is either positively correlated with both water and light, or positively correlated with one of them and negatively with the other. Ecosystem models largely underestimate positive correlations with light and overestimate positive correlations with water. In the second study, I focus on the effect of land cover change in photosynthetic activity and transpiration in a highly deforested region in the Amazon. I find that land cover change decreases tropical forests photosynthetic activity and transpiration during the dry season. Also, land cover change increases the range of photosynthetic activity and transpiration in forests and shrublands. These effects are intensified with increasing land cover change. In the last project, I quantify the amount of change in evapotranspiration due to land cover change in the entire Amazon basin. Our remote sensing-derived estimates are well aligned with model predictions published in the past three decades. These results increase our confidence in climate models representation of evapotranspiration in the Amazon.</p><p>Findings from this dissertation highlight (1) the importance of the close relationship between climate and photosynthetic activity and (2) how land cover change is altering that relationship. We hope our results can build on our knowledge about tropical ecosystems and how they could change in the future. We also expect our analysis to be used for model benchmarking and tropical ecosystem monitoring.</p>

Orientador: Liliane Santos de Camargos / Resumo: O manganês é um micronutriente que se enquadra no critério de essencialidade das plantas, no entanto sua presença altera o teor de outros nutrientes como o fósforo, quando aplicado em solo. A leguminosa herbácea tropical Stizolobium aterrimum Piper & Tracy (Mucuna-preta) é uma planta constantemente utilizada em sistema de cultura consorciada para conservação de matéria orgânica, por conta de sua biomassa. Desta forma, o trabalho visa a utilização dessa leguminosa como tolerante e com potencial fitorremediador para a retirada de manganês em concentrações tóxicas do solo. Portanto. foi avaliado seu crescimento e metabolismo em solos com concentrações tóxicas de manganês, analisando massa fresca, seca, indicadores de estresse oxidante, parâmetros da fotossíntese e metabólitos (aminoácidos, açucares solúveis totais, clorofila, ureídeos, proteína, nitrato e amônia), índice de tolerância e quantificação de manganês nos tecidos. Os dados foram avaliados por análise de variância e Soctt-Knott a 5% de probabilidade, utilizando o software SISVAR®. S aterrimum, consegue germinar em solos com altas concentrações de manganês; produz grande quantidade de biomassa seca e fresca mesmo em doses potencialmente tóxicas de manganês, não apresenta indicadores de estresse oxidativo; S. aterrimum é uma planta tolerante e com potencial de fitorremdiador para manganês. / Abstract: Manganese is a micronutrient that meets the criteria of essentiality of plants, however its presence changes the content of other nutrients such as phosphorus, when applied to soil. The tropical herbaceous legume Stizolobium aterrimum Piper & Tracy (Mucuna-preta) is a plant constantly used in a intercropping system for the conservation of organic matter, due to its biomass. Thus, the work aims to use this legume as a tolerant and with phytoremediation potential for the removal of manganese in toxic concentrations of the soil. Therefore. its growth and metabolism in soils with toxic concentrations of manganese was evaluated, analyzing fresh, dry mass, oxidative stress indicators, photosynthesis parameters and metabolites (amino acids, total soluble sugars, chlorophyll, ureides, protein, nitrate and ammonia), tolerance and quantification of manganese in tissues. The data were evaluated by analysis of variance and Soctt-Knott at 5% probability, using the SISVAR® software. S aterrimum, can germinate in soil with high concentrations of manganese; it produces a large amount of dry and fresh biomass even in potentially toxic doses of manganese, it does not show oxidative stress indicators; S. aterrimum is a tolerant plant with potential for phytoremediation for manganese. / Mestre

Chickpea (Cicer arietinum) is an important legume crop globally ranked third after dry bean (Phaseolus vulgaris) and field pea (Pisum sativum). It constitutes 20% of the total global pulse production and around 95% of its production and consumption takes place in developing countries. Major constraints to chickpea production in sub Saharan Africa (SSA) have broadly been related to abiotic stresses, particularly drought and heat stresses, predicted to increase due to the global climatic changes.Dueto the imperativeness of research for identifying heat tolerance markers for potential chickpea genotype selection, in chapter two of the thesis, the response of four chickpea genotypes to a natural temperature gradient in the field was assessed using chlorophyll fluorescence, non-structural carbohydrate, gas exchange and grain yield. Field experiments were carried out in two winter seasons at three locations with known differences in temperature in NE South Africa. Results showed two genotypes (Acc#3 and Acc#7) were tolerant to heat stress with an Fᵥ/Fₘ of 0.83-0.85 at the warmer site, while the two sensitive genotypes (Acc#RR-2 and Acc#8) showed lower Fᵥ/Fₘ of 0.78-0.80. Both chlorophyll fluorescence measurements: dark-adapted Fᵥ/Fₘ and Fq'/Fₘ' (where Fq' =Fₘ'–F) measured at comparable high light levels correlated positively with grain yield. The two tolerant genotypes also showed higher photosynthetic rates,starch, sucrose and grain yield than the sensitive genotypes at the warmer site. However, these parameters were consistently higher at the cooler than at the warmer sites. It was concluded that genotypes Acc#RR-3 and Acc#7 are heat tolerant and chlorophyll fluorescence and leaf carbohydrates are suitable tools for selection of heat tolerant chickpea genotypes under field conditions. The coolest site of Polokwane showed favourable conditions for chickpea production.Heat and drought stresses are two abioticfactors that often occur simultaneously and are predicted to increase, consequently hampering plant growth. Response of different species to either stresses is well documented but information on the response of the same genotypes to both stresses in chickpea is limited. We aimed to determine whether previously noted heat stress tolerant genotype (Acc#7) is drought tolerant and the heat sensitive (Acc#8) is drought sensitive, and whether intermittent moisture supply at vegetative stage would induce priming effect to later drought at flowering. At vegetative stage, plants were divided into three groups, non-stressed (watered to 75% field capacity (FC), severe water stress (moisture-withholding for 14 days) and treated to 40% FC throughout the experiment (mild-stress), with recovery for the severely stressed plants after which they were stressed (double-stress) at flowering. Drought treatments at vegetative and flowering growth stages decreased physiological parameters and biomass accumulation in both genotypesexcept low water supply at 40% FC that decreased biomass in Acc#7 but not Acc#8. Double drought stress resulted in priming effect in Acc#7, having higher biomass, chlorophyll fluorescence, stomatal conductance, net photosynthesis, and relative water content in comparison to the introduction of stress only at flowering growth stage, as well as in comparison to Acc#8. These results showed that both Acc#7 and Acc#8 are sensitive to drought whereas after priming Acc#7 is better acclimated to drought than Acc#8 associated with osmotic adjustment on leaf relative water content (RWC) and higher capacity to protect photosynthetic activity, making Acc#7 potentially ideal for areas associated with intermittent drought spells. This observation, however, disapproved the hypothesis that Acc#7 is more drought tolerant than Acc#8 but is rather better acclimated than Acc#8, because of its superiority only in primed plants and not those stressed only at either vegetative or flowering stages. The findings emphasise the importance of matching chickpea physiological performance to expected rainfall amounts and distribution in drought prone areas during genotype selection. Chapter four of the thesis was an interrogative proteome analysis of the differences in the heat tolerant and sensitive chickpea (Cicer arietinumL.; Fabaceae) genotypes along a temperature gradient under field conditions which will help in identifying the molecular mechanisms involved in the crop's tolerance. Few studies have thus far combined chickpea physiological and proteome analysis to elucidate the changes in abundance and/or activity of relevant enzymes and expression of heat responsive proteins. In this study, analyses of chlorophyll concentrations, gas exchange, flavonoids and anthocyanin concentrations from a chamber experiment, as well as proteomic parameters from field studies in both the heat tolerant and sensitive genotypes are presented. The heat tolerant genotype Acc#7 maintained unaltered physiological performance at flowering growth stage when exposed to high (35/30°C) and moderate (30/25°C) heat stress, under climate chamber conditions compared to the two heat susceptible genotypes (Acc#RR-2 and Acc#8). Results from the proteomic studies showed an up-regulation in proteins related to protein synthesis (e.g. ribulose bisphosphate carboxylase/oxygenase activase), intracellular traffic (e.g. mitochondrial dicarboxylate/tricarboxylate transporter DTC), defence (e.g. HSP70) and transport (e.g. GTP-binding protein SAR1A-like) in heat tolerant Acc#7 compared to the susceptible Acc#8. Results from KEGG analyses support the involvement of probable sucrose-phosphate synthase and sucrose-phosphate phosphatase proteins in the starch and sucrose pathway,that were up-regulated in the heat tolerant genotype Acc#7. This result was in support of our earlier report where tolerant genotype Acc#7 had higher leaf starch and sucrose concentrations in comparison to the susceptible genotype Acc#8. The presence of these differentially regulated proteins including HSP70, ribulose bisphosphate carboxylase/oxygenase activase, plastocyanin and protoporphyrinogen oxidase shows their potential role in field grown chickpea tolerance to heat stress at flowering growth stage. In conclusion, chlorophyll fluorescence (both Fᵥ/Fₘ and Fq'/Fₘ') and leaf carbohydrates were identified as selection markers that can potentially be used for chickpea phenotyping for heat stress under field conditions with the chlorophyll fluorescence parameters correlating positively with seed yield. Due to its higher biomass, chlorophyll fluorescence (Fᵥ/Fₘ), stomatal conductance, net photosynthesis and RWC, heat tolerant genotype Acc#7 was identified to have better adaptive tolerance to drought stress after priming through exposure to intermittent dry spells than Acc#8. Furthermore, under controlled climate chamber conditions, Acc#7 consistently showed characteristics of tolerance to heat stress while Acc#RR-2 and Acc#8 were heat susceptible. Higher chlorophyll fluorescence, grain yield, chlorophyll concentrations, gas exchange, flavonoids and anthocyanin concentrations for Acc#7 compared to Acc#8 in the climate chamber was further validated by the higher up-regulation of proteins involved in protein synthesis, intracellular traffic, defence and transport in Acc#7 compared to Acc#8. The incorporation of proteomics in heat and drought stress studies will potentially help further the understanding of mechanisms by which the crop responds to these stresses.

Développer de nouvelles sources d’énergie respectueuses de l’environnement est un des enjeux majeur de nos sociétés développées. Pour espérer la pérennité de notre espèce sur cette planète, il est indispensable de développer les sources d'énergie renouvelable ; permettant de nous affranchir de la dépendance aux énergies fossiles polluantes et dont les stocks s’épuisent. Il appartient aux scientifiques d’apporter leurs contributions à cet important défi que l’on appelle la transition énergétique et pour ça d’aider à développer une énergie idéale qui ne produirait pas de déchet polluant, serait très efficace et largement disponible. L'énergie solaire représente un excellent candidat car elle est de loin la plus abondante et prometteuse source d’énergie propre. D'importants efforts sont donc menés pour développer les technologies solaires, notamment la photosynthèse artificielle.La photosynthèse artificielle a vu le jour il y a une centaine d’années et fait l’objet de beaucoup d’intérêt et de recherche. Cette technologie cherche à imiter la photosynthèse naturelle réalisée par les plantes; et cela afin de stocker l’énergie provenant du Soleil dans des composés utilisables par l’Homme. La photosynthèse artificielle consiste en l’élaboration de systèmes synthétiques capables sous impulsion lumineuse de réaliser la décomposition de l’eau de manière catalytique, pour générer du dihydrogène ou des produits issus de la réduction du CO2, que l’on appelle combustibles solaires car à haut potentiel énergétique. En effet, la photosynthèse débute par la photo-catalyse de l’oxydation de l’eau, qui permet d’extirper les électrons et les protons des molécules d’eau. Ce sont ces électrons et protons qui seront utilisés par un catalyseur pour produire les combustibles solaires.Depuis peu, une véritable volonté de comprendre les mécanismes qui ont lieu lors de ces réactions catalysées semble apparaitre. Ces réactions mettent en jeu des transferts électroniques multiples photo-induits et cela rend leur étude assez compliquée. Grâce à des avancées technologiques importantes, nous avons étudié de manière plus approfondies plusieurs systèmes photo-catalytiques afin d’en tirer des savoirs permettant de rationaliser le design et d’améliorer les capacités des futurs systèmes développés. Ces avancées techniques ont été possibles grâce à des collaborations interdisciplinaires entre des chimistes et des physiciens et ont permis de développer un montage d’absorption transitoire « double-pump» afin de caractériser les espèces transitoires formées et de retracer les mécanismes lors de deux transferts électroniques photo-induits successifs.Dans la seconde partie de ce travail, de nouveaux catalyseurs ont été développé pour la réaction de photo-catalyse de l’oxydation de l’eau. La majorité des études menées jusqu’ici sur le sujet ont porté sur des systèmes moléculaires, mais le manque de robustesse et de réutilisabilité des catalyseurs homogènes a poussé la recherche vers le domaine des matériaux. Ainsi depuis une quarantaine d’années des systèmes photo-catalytiques hétérogènes ont été développé. Nous avons explorés deux types de matériaux, des nanoparticules catalyseurs dans des systèmes photo-catalytiques, et des polymères qui à eux seuls sont capables de réaliser l’ensemble des fonctions nécessaires à la photo-catalyse d’une réaction telle que l’oxydation de l’eau sous irradiation de lumière visible.Ainsi au cours de cette thèse nous avons tenté par deux approches d’avancer les connaissances et le développement de la photosynthèse artificielle. Une solution encore peu développée au problème énergétique auquel notre société fait face est le recours aux combustibles solaires, et il est grand temps que la recherche avance et que la transition énergétique s’impose plus efficacement et largement. / Developpment of environment-friendly sources of energy is one of the stakes major for our societies. To hope for the sustainability of Humans on Earth, it is essential to change our consumer habits on energetics by breaking our dependance on fossil fuels, which use leads to ecological desasters and which stocks are running out. The key of this important challenge is the growth of renewable energy sources, and this is called energy transition. The ideal energy would not produce any polluting waste, would be efficient and widely available. Solar energy is an excellent candidate because it is by far the most abundant and promising source of clean energy. Thus, important efforts are made to developp the solar technologies, including artificial photosynthesis.Artificial photosynthesis was created a century ago and is the focus of many interests and researchs. This technology aims at mimicking the natural photosynthesis realized by plants ; and that in order to store the energy coming from the Sun irriadiation in compounds that can be used at demand. Artificial photosynthesis consists in the elaboration of synthetic systems able under light impulsion to realize the water splitting/decomposition reactions in a catalytique way, generating hydrogène or CO2 reduction products, which are called solar fuels thanks to their high energetic potentials. Indeed, photosynthesis begins with the photo-catalysis of water oxidation, which extirpates the electrons and protons of water molecules. And it is these electrons and protons which will be used to produce the solar fuels.Recently, a real commitment to understand deaply the mechanisms that take place during these catalysed reactions seems to appear. These transformations involve multiple photo-induced electron transfers and it returns their study relatively complicated. Thanks to technological breakthroughs, we studied in a thorough way several photocatalytic systems to draw knowledges ; allowing the rationalisation of the design and then the efficiency improvement of future developped systems. These technical advances were possible thanks to interdisciplinary collaborations between chemists and physicists and led to the developpment of a set-up of « double-pump » transient absorption, that enables to characterize the transient species formed and to track down the pathways during two successive photoinduced electron transfers.In the second part of this work, new catalysts were developped for the photocatalysis of water oxidation reaction. The big majority of the studies led so far on this subject concerned molecular systems, but the lack of robustness and reusability of homogeneous catalysts pushed the research towards materials area. Since about forty years, heterogeneous systems were developped for photocatalysis of several reactions. We explored two types of materials, nanoparticules as catalyst in photocatalytic systems ; and polymers that are able on their own to realize all the functions required for the photocatalysis of a reaction such as water oxidation under visible light irradiation.Thus, during this PhD we tried by two approaches to increase the knowledges and the development of artificial photosynthesis. A solution that is still under-developped to fix the energetic issue our society is facing to, is the use of solar fuels ; and it’s imperative for the research to move forward and that energy transition prevails more effectively and widely.