The marine environment is an important habitat where many processes occur that affect life conditions on earth. Macrophytes and planktonic oxygen evolvers are an essential component for almost all marine life forms and have developed in an environment that differs largely from the terrestrial habitats. For instance in regards to available ionic forms of inorganic carbon and moving water masses which affects incoming light. It is therefore relevant to examine the physiology of algae and marine plants to identify their unique features and differences to terrestrial plants that once orginated from algae. By using chlorophyll fluorescence measurements alone or combined with measurements of oxygen evolution and protein analysis photosynthetic strategies to withstand excess energy have been evaluated under a variety of experimental conditions. Furthermore metabolic pathways involved in energy transfer from photosynthesis to the site of active carbon uptake have been examined. The following was found: * The ratio between photosynthetic gross oxygen evolution and estimated electron transport rate varies in Ulva spp depending on previous history of light and dark exposures. To obtain P/I curves with ratios close to the theoretical 1:4 value, measurements should be performed on separate pieces of tissue at each irradiance level. * Under carbon deficient conditions, the estimated ETR is larger than the gross oxygen evolution, which may be due to the so called “water-water” cycle and absorption changes in PSII which are not corrected for in the calculation of ETR. * Upon exposure to high irradiances (1500 µmol photons m-2s-1) the PSII core protein D1 is broken down with a concomittant reduction in ETR in Ulva spp. With the decrease in electron transport between PSII and PSI the acidification of the lumen decreases and the ability to dissipate excess energy as heat. At prolonged irradiance, an acclimation occurs with a lesser or no breakdown of D1 indicating an additional photo-protective strategy other than heat dissipation. * Laminaria saccharina is dependent on mitochondrial respiration for active utilization of bicarbonate. By extruding protons outside the plasmalemma an acidification takes place that favors the conversion of bicarbonate into carbon dioxide that then can diffuse in to the cell. These proton pumps are driven by ATP supplied to a large degree from mitochondria, likely through the reductant NADPH produced photochemically. * The marine angiosperm Zostera marina is dependent on mitochondrial respiration for utilization of bicarbonate in a manner similar to that in Laminaria saccharina . However, the water-water cycle may supply additional ATP to the proton pumps in Zostera marina. Both species exhibit a lag-phase at the onset of illumination after a dark incubation period and at least part of this lag-phase is due to a lag in an activation of mitochondrial supported bicarbonate utilization. It is clear that the marine environment holds complex plant and algae species and much is still to discover about the oxygen evolvers that grow beneath the water surface.

The green algae of the genus Halimeda Lamouroux (Chlorophyta, Bryopsidales) and the encrusting loose-lying red coralline algae (Rhodophyta, Corallinales) known as rhodoliths are abundant and widespread in all oceans. They significantly contribute to primary productivity while alive and production of CaCO3 rich sediment materials on death and decay. Carbonate rich sediments are important components in the formation of Coral Reefs and as sources of inorganic carbon (influx) in tropical and subtropical marine environments. This study was initiated to attempt to assess their ecological significance with regard to the above mentioned roles in a tropical lagoon system, Chwaka bay (Indian Ocean), and to address some specific objectives on the genus Halimeda (Chlorophyta, Bryopsidales) and the loose-lying coralline algae (rhodoliths). Four Halimeda species were taxonomically identified in the area. The species identified are the most common inhabitants of the world’s tropical and subtropical marine environments, and no new species were encountered. Using Satellite remote sensing technique in combination with the percentage cover data obtained from ground-truthing field work conducted in the area using quadrants, the spatial and seasonal changes of Submerged Aquatic Macrophytes (SAV) were evaluated. SAV percentage cover through ground-truthing was; 24.4% seagrass, 16% mixed Halimeda spp., 5.3% other macroalgae species while 54.3% remained unvegetated. No significant changes in SAV cover was observed for the period investigated, except in some smaller regions where both loss and gains occurred. The structural complexity of SAV (shoot density, above-ground biomass and canopy height) for most common seagrass communities from six meadows, dominated by Thalassia hemprichii, Enhalus acoroides and Thalassodendron ciliatum, as well as mixed meadows, were estimated and evaluated. Relative growth of Halimeda species was up to 1 segment tip-1 day-1. The number of segments produced was highest in hot season. Differences between the numbers of segments produced were insignificant between the two sites investigated. The C/N ratios obtained probably shows that Halimeda species experience nitrogen limitation in the area and may be a factor among others responsible for the varying growth of species obtained. However, this can be a normal ratio for calcified algae due to high CaCO3 content in their tissues. Standing biomass of mixed Halimeda species averaged between 500-600 g dw m-2 over the bay, while the mean cover in Halimeda meadows was about 1560 g dw m-2. Carbonate production in Halimeda beds varied between 17-57 g CaCO3 m-2 day-1 and for H. macroloba between 12-91 g CaCO3 m-2 day-1. This indicates a high annual input of carbonate in the area. Decomposition of Halimeda using litter bag experiments at site I and II gave a decomposition rate (k) of 0.0064 and k = 0.0091 day-1 ash-free dry weight (AFDW) respectively. Hence it would take 76-103 days for 50% of the materials to decompose. Adding inhibitors or varying the pH significantly reduced inorganic carbon uptake, and demonstrated that the two photosynthesis and calcification were linked. Addition of TRIS strongly inhibited photosynthesis but not calcification, suggesting the involvement of proton pumps in the localized low pH acid zones and high pH basic zones. The high pH zones were maintained by the proton pumps maintaining high calcification, while TRIS was competing for proton uptake from acid zones causing photosynthesis to drop. Rhodoliths were found to maintain high productivity at a temperature of 34oC, and even at 37oC. It is therefore concluded that, rhodoliths are well adapted to high temperatures and excess light, a behaviour which enables them to thrive even in intertidal areas.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3353. Adviser: Stephen P. Long. Includes bibliographical references (leaves 109-116) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--Ohio State University, 1967. / Includes bibliographical references. Available online via OhioLINK's ETD Center

No description available.

Cyanobacteria are an ancient and globally distributed group of photosynthetic prokaryotes including species capable of fixing atmospheric dinitrogen (N2) into biologically available ammonia via the enzyme complex nitrogenase. The ability to form symbiotic interactions with eukaryotic hosts is a notable feature of cyanobacteria and one which, via an ancient endosymbiotic event, led to the evolution of chloroplasts and eventually to the plant dominated biosphere of the globe. Some cyanobacteria are still symbiotically competent and form symbiotic associations with eukaryotes ranging from unicellular organisms to complex plants. Among contemporary plant-cyanobacteria associations, the symbiosis formed between the small fast-growing aquatic fern Azolla and its cyanobacterial symbiont (cyanobiont), harboured in specialized cavities in each Azolla leaf, is the only one which is perpetual and in which the cyanobiont has lost its free-living capacity, suggesting a long-lasting co-evolution between the two partners. In this study, the genome of the cyanobiont in Azolla filiculoides was sequenced to completion and analysed. The results revealed that the genome is in an eroding state, evidenced by a high proportion of pseudogenes and transposable elements. Loss of function was most predominant in genetic categories related to uptake and metabolism of nutrients, response to environmental stimuli and in the DNA maintenance machinery. Conversely, function was retained in key symbiotic processes such as nitrogen-fixation and cell differentiation. A comparative analysis shows that the size of the cyanobiont genome has remained relatively stable, and that few genes have been completely eliminated, since the symbiotic establishment. Indications of genes acquired via horizontal gene transfer were discovered in thec yanobiont genome, some of which may have originated from the bacterial community in the Azolla leaf-cavities. It is concluded that the perpetual nature of the Azolla symbiosis has resulted in pronounced ongoing streamlining of the cyanobiont genome around core symbiotic functions, a process not described previously for complex cyanobacteria or for any bacterial plant symbiont. Further, the status of the genome indicates that the cyanobiont is at an early stage of adapting to its host-restricted environment and continued co-evolution with the plant may result in additional genome reductions. However, although a vertical transmission process is already established, the unusual extracellular location of the cyanobiont and the intricate nature of the symbiosis, may still impose restrictions on such a reductive process. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript.</p>

In spite of the fact that it is one of the most widely researched subjects in plant biology, the physiology of salt tolerance is still not well understood. This research was undertaken to investigate salt tolerance in the extreme halophyte, Salicornia bigelovii Torr. Halophytes, plants that are naturally salt tolerant, are well suited to research on salt tolerance because millions of years of evolution have fine tuned their adaptation to high salinity to the extent that their growth is inhibited when they are grown in reduced salinity. S. bigelovii was grown in different concentrations of NaCl and growth responses were compared. My emphasis was on salinity effects on cell wall extensibility, wall yielding threshold (minimum turgor required for growth), and water relations. When S. bigelovii was grown in low salinity, relative growth rate was slower, fresh and dry weight, relative water content and succulence were reduced, and both epidermal and cortex parenchyma cells were smaller. The plants also accumulated less Na⁺ and more K⁺, Ca²⁺ and Mg²⁺. These results prompted two specific questions. Was the excess Ca²⁺ accumulated by the plants grown in low salinity bound to cell walls and did it cause reduced cell wall extensibility and increased yield threshold? Was growth inhibition a consequence of low turgor due disturbances in water relations? Even though there was three times more Ca²⁺ in the walls of the plants grown in I salinity, cell wall extensibility was not significantly different between salinity treatments. However, the wall yielding threshold of the plants grown in low salinity was significantly lower. Turgor was also significantly lower in these plants. But, since the minimum turgor required for growth was even lower, reduced turgor was not responsible for growth inhibition. Based upon the results of this research, I have concluded that growth inhibition in S. bigelovii in reduced salinity was not due to disturbances in water relations nor was it the result of detrimental changes in cell wall properties. It is becoming increasingly clear that specific ion effects play an important role in limiting the growth of S. bigelovii in low salinity. This research has led to the identification of several new directions for future investigation into the salt tolerance mechanisms of this unique plant.

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

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

Soybean contains a range of compounds with putative health benefits including isoflavones and tocopherols. A study was conducted to determine the effects on these compounds of high temperature stress imposed at specific development stages. Isoflavones and tocopherols response was the greatest when stress occurred during the R5-8 development stages (seed formation) and less during all other stages. Stress imposed at the R5-8 stages reduced total isoflavones concentration by an average of 85% compared to the control, while increasing α-tocopherol by as much as 752%. Another study was conducted to determine the effects of high temperature stress during the R5-8 plant development stages on the expression of four key genes (i.e., CHS7, CHS8, IFS1 & IFS2) involved in isoflavone synthesis. High temperature stress had a large effect on the expression of all genes in both seeds and pods; however, there was no correlation between gene expression and isoflavones concentration. / Le soja contient plusieurs composés ayant des effets bénéfiques sur la sante humaine. Une première étude a été réalisée afin de déterminer les effets d'un stress de haute température imposé à des stades de développement spécifiques sur ces composés. La réponse des isoflavones et des tocopherols a été maximale lorsque que le stress a été imposé durant les stades R5-8 (stades formation des grains) et durant tout les stades de développement, ces traitements réduisant la concentration en isoflavone total par 85% en moyenne lorsque comparé à un traitement contrôle, et augmentant la α-tocopherol par autant que 752%. Une deuxième étude a été réalisée afin de déterminer les effets d'un stress de haute température durant les stades R5-8 sur l'expression de quatre gènes clefs (i.e., CHS7, CHS8, IFS1 & IFS2) impliques dans la synthèse des isoflavones. Le traitement de stress a eu un important effet sur tous les gènes dans les gousses et les grains ; cependant il n'y avait pas de corrélation entre l'expression génique et les concentrations en isoflavones.