From the Proceedings of the 1977 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 15-16, 1977, Las Vegas, Nevada / Relative water content (RWC), water potential (P), and gas exchange were measured on saltcedar at the Bernardo, New Mexico, lysimeter site. RWC and s were closely correlated; but, water potential measurements, taken with a pressure bomb, were more convenient and reliable. RWC and r decreased sharply from sunup until about 0900, when minimum values of about -26 bars T or 80% RWC were reached. Water status then remained constant or improved slightly through late afternoon. Transpiration rates typically remained high until about noon and then began a steady, gradual decrease that continued throughout the afternoon. The data suggest that water stress may be a factor in initiating stomatal closure; however, transpiration continued to decline despite a constant or improved leaf water status. Maximum net photosynthetic rates occurred by 0900, and depressions throughout the remainder of the day were largely accounted for by increased leaf temperatures. Afternoon depressions in transpiration and photosynthesis occurred in twigs held at constant temperature and relative humidity, suggesting that a diurnal rhythm may be involved in control of gas exchange. Water status of plants growing on the lysimeters was comparable to that of plants in adjacent natural stands; gas exchange rates were slightly higher for the lysimeter-grown plants.

Adaptation to environmental changes is important for the survival of living organisms. Under extreme abiotic conditions, organic molecules (such as lipids, proteins and nucleic acids) are prone to damage. Under these conditions stress response mechanisms are activated, either to prevent the source of damage or to promote the rapid turnover of damaged molecules. Like all photoautotrophic organisms, cyanobacteria are sensitive to high light intensity and oxidative stress, which induces damage to the photosynthetic apparatus. My thesis is divided in two subjects related to particular stress responses in the cyanobacterium Synechocystis sp. PCC 6803: 1) the role of Deg/HtrA proteases and 2) investigations on the small CAB-like proteins. Deg/HtrA proteases are ATP-independent serine endopeptidases with a characteristic C-terminal PDZ domain. These proteases are largely dispersed among living organisms, with many different functions, mostly involved in protein quality control. The genome of Synechocystis sp. PCC 6803 contains three genes coding for Deg/HtrA proteases: HtrA, HhoA and HhoB. These proteases are essential for survival under high light and heat stress, and may overlap in their functions. During my Ph.D. studies I focused on the identification of the precise localization of the Deg/HtrA proteases in the cyanobacterial cell, analyzed the biochemical properties of recombinant Synechocystis Deg/HtrA proteases in vitro and adopted proteomic and metabolomic approaches to study the physiological importance of these proteases. My data show that Deg/HtrA proteases are not only important in stress response mechanisms under adverse conditions, but are also involved in the stabilization of important physiological processes, such as polysaccharides biosynthesis and peptidoglycan turnover. The small CAB-like proteins (SCPs) belong to the light harvesting-like family of stress induced proteins and are thought to be involved in the photoprotection of the photosynthetic apparatus. Five small CAB-like proteins where identified in Synechocystis sp. PCC 6803 (ScpA-E). In my studies I identified another relative to the SCPs, LilA, which I found to be co-transcribed with ScpD. I also focused on the subcellular localization and identification of potential interaction partners of the SCPs.

No description available.

Although a common plant response to environmental gradients, leaf trait plasticity is often uncharted in agroforestry systems. The objective of this study was to examine the effect of a i) local-scale gradient (light, nutrients) induced by shade tree diversity and ii) large-scale gradient (climato-edaphic) induced by altitude on coffee plant response on multiple agroforestry research farms in Costa Rica. Results show large variability of coffee traits: leaf photosynthetic rates, specific leaf area (SLA) and number of fruiting nodes deviate along both gradients. Mean SLA increased with increasing shade tree diversity. However, with increasing altitude, full sun coffee photosynthesized at higher rates than shaded coffee. Concurrently, other coffee leaf physiological and morphological traits differentiated between full sun and shaded coffee with increasing altitude. Results suggest soil moisture and light availability dominate environmental correlates to intraspecific coffee trait plasticity, providing insight to sources of coffee performance variability in monoculture and agroforestry systems.

Although a common plant response to environmental gradients, leaf trait plasticity is often uncharted in agroforestry systems. The objective of this study was to examine the effect of a i) local-scale gradient (light, nutrients) induced by shade tree diversity and ii) large-scale gradient (climato-edaphic) induced by altitude on coffee plant response on multiple agroforestry research farms in Costa Rica. Results show large variability of coffee traits: leaf photosynthetic rates, specific leaf area (SLA) and number of fruiting nodes deviate along both gradients. Mean SLA increased with increasing shade tree diversity. However, with increasing altitude, full sun coffee photosynthesized at higher rates than shaded coffee. Concurrently, other coffee leaf physiological and morphological traits differentiated between full sun and shaded coffee with increasing altitude. Results suggest soil moisture and light availability dominate environmental correlates to intraspecific coffee trait plasticity, providing insight to sources of coffee performance variability in monoculture and agroforestry systems.

Mit zunehmender Meereshöhe werden die Wachstumsbedingungen in tropischen Bergregionen im Allgemeinen ungünstiger, was sich in einer sinkenden Nährstoffverfügbarkeit, sinkenden Temperaturen und sinkendem CO2-Partialdruck zeigt. In tropischen Bergregenwäldern führen verminderte Abbauraten in größeren Höhen einerseits zu dicken organische Auflageschichten und andererseits in Kombination mit verminderten Mineralisierungs- und Nitrifizierungsraten zu Veränderungen in der Verfügbarkeit der verschiedenen Stickstoffformen, und es gibt Nachweise einer Limitierung der Produktivität dieser Wälder durch Stickstoff. Auf welche Weise sich die Photosynthesekapazität (Amax) tropischer Bäume einerseits und die Stickstoffaufnahmekapazität und Präferenz für einzelne Stickstoffformen andererseits an die veränderten Umweltbedingungen entlang von Höhengradienten adaptieren ist nicht genau bekannt. Die vorliegende Untersuchung wurde in drei tropischen Bergregenwäldern durchgeführt, die entlang eines Höhengradienten auf 1000, 2000 und 3000 m ü. NN in Südequador liegen. Das Ziel war es, (1) die Photosynthesekapazität ausgewachsener tropischer Bäume entlang eines Höhengradienten mit Hilfe von Gaswechselmessungen zu bestimmen und die Effekte von Temperatur, CO2-Partialdruck und Nährstoffverfügbarkeit auf die Photosynthese zu quantifizieren und (2) Veränderungen in der Verwendung von Nitrat, Ammonium und organischen Stickstoffquellen durch tropische Waldbäume mit der Meereshöhe mittels einer Tracer-Untersuchung mit stabilen Isotopen an Jungpflanzen zu untersuchen. Mittelwerte der lichtgesättigten Photosyntheserate (Asat) auf Bestandeseben betrugen 8.8, 11.3 und 7.2 µmol CO2 m-2 s-1, die der Dunkelatmung (RD) 0.8, 0.6 und 0.7 µmol CO2 m-2 s-1 jeweils auf 1000, 2000 and 3000 m Meereshöhe, ohne einen signifikanten Höhentrend. Die Einordnung unserer Daten in den Kontext eines pantropischen Asat-Datensatzes von tropischen Bäumen (c. 170 Arten an 18 Standorten unterschiedlicher Meereshöhe) zeigte, dass das flächenbezogene Asat in tropischen Bergen im Mittel 1.3 µmol CO2 m-2 s-1 pro km Höhenzunahme abnimmt (bzw. 0.2 µmol CO2 m-2 s-1 pro K Temperaturabnahme). Die Abnahme von Asat trat auf, obwohl die Blattmasse je Fläche mit der Höhe zunahm. Eine verminderte Photosyntheserate und eine reduzierte Bestandesblattfläche bewirken gemeinsam eine Verringerung der Kohlenstoffaufnahme des Kronenraums mit der Meereshöhe in tropischen Bergregionen. Der Phosphorgehalt pro Blattmasse war der Faktor, der Amax entlang des Höhengradienten hauptsächlich beeinflusste, während die Effekte von Blattstickstoff, Temperatur und CO2-Partialdruck nicht signifikant waren. Amax erfuhr einen teilweisen und RD einen vollständigen homöostatischen Ausgleich als Reaktion auf die Verminderung von Temperatur und CO2-Partialdruck in größeren Höhen, was hauptsächlich durch eine stark reduzierte spezifische Blattfläche (SLA) und die daraus entstehende Zunahme von Blattstickstoff und -phosphor je Blattfläche bedingt war, während keine Zunahme der Karboxylierungseffizienz festgestellt wurde. Wir schlussfolgern, dass die Verminderung von SLA und Gesamtblattfläche mit der Meereshöhe die Kohlenstoffaufnahme von tropischen Wäldern in großen Meereshöhen deutlich stärker bestimmen als adaptive physiologische Modifizierungen des Photsyntheseapparates. Jungpflanzen von sechs Baumarten unterschieden sich hinsichtlich ihrer Präferenz für verschieden Stickstoffformen, allerdings schienen weder das Amonium- und Nitratvorkommen im Boden noch die Meereshöhe die Präferenz zu beeinflussen. Zwei Arten (jeweils die, mit den höchsten Wachstumsraten) bevorzugten Amonium gegenüber Nitrat, während die restlichen vier Arten Nitrat und Amonium mit ähnlichen Raten aufnahmen, wenn beide Stickstofformen verfügbar waren. Nach der Gabe von 15N13C-Glyzin zeigte sich bei drei Arten eine signifikante Akkumulierung von 13C in der Biomasse (zwei Arten mit arbuskulären Mykorrhiza und eine Art mit Ektomykorrhiza) zusätzlich zu einer signifikanten Akkumulierung von 15N, was darauf hindeutet, dass Bäume in tropischen Bergregenwäldern organische Stickstoffverbindungen unabhängig vom Typ ihrer Mykorrhizierung aufnehmen können.

Sink limitations in plants reduce the potential for photosynthesis and yield, particularly under conditions that favour enhanced source activity such as elevated CO2 (EC). Dark respiration, considered catabolic, has rarely been exploited to enhance sink activity in plants. Arabidopsis thaliana L. lines with partially-suppressed mitochondrial pyruvate dehydrogenase (mtPDH) kinase (mtPDHK), a negative post-translational regulator of the mtPDH complex, was shown previously to have both elevated mtPDH complex activity and increased seed weight and oil content at ambient CO2 (AC), suggesting an enhancement of sink activity. The mtPDH links glycolysis with the tricarboxylic acid (TCA) cycle. It was hypothesized that Arabidopsis having suppressed mtPDHK will display their greatest plant productivity at EC through a combined enhancement of source and sink activities. Control and transgenic Arabidopsis having either constitutive or seed-specific expression of antisense mtPDHK were grown at either AC or EC. Expression of mtPDHK and mtPDH complex activity in rosette leaves and reproductive tissues were measured, which required the development of an assay to quantify mtPDH activity. Vegetative and reproductive growth over time, seed oil parameters, and leaf net C exchange were also quantified. A parabolic relationship was found between mtPDHK expression and mtPDH activity, reflecting a role for mtPDH in balancing photosynthetic and respiratory processes. A number of growth and seed oil parameters were improved in transgenic lines, particularly at EC; many of these parameters showed a significant linear or quadratic correlation with mtPDHK expression and mtPDH activity. The proportion of very long chain fatty acids was increased in transgenic lines. Leaf net C exchange was enhanced at AC and EC, and particularly in lines showing repression of mtPDHK. The greatest enhancement in total seed and oil productivity was found for the constitutive lines 104 and 31 at EC (up to 2.8 times). These two lines exhibited a significant increase in inflorescence size, an increase in leaf water use efficiency, the lowest rate of mtPDH complex inactivation by ATP, and an intermediary enhancement of mtPDH complex activity in seeds. Thus, it is concluded that the mtPDH plays a key role in regulating sink and source activities in plants. / Natural Sciences and Engineering Research Council (NSERC) through the Green Crop Networks Research Network; Ontario Graduate Scholarship; Syngenta Graduate Scholarship; Ball Farm Services and Agrico Canada Ltd. Scholarship; Mrs. Fred Ball Scholarship; Arthur D. Latornell Scholarship; Hoskins Scholarship; Robb Travel Grant; Registrars and the Deans Scholarship and travel awards and bursaries from the University of Guelph, and the Ontario Agricultural College.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

The current research project investigated the anoxygenic phototrophic and metal(loid) transforming bacteria of hypersaline and deep ocean hydrothermal environments. The East German Creek brine springs, an unusual flowing hypersaline system, was enumerated using classical techniques. Subterranean sulfide supported purple sulfur and nonsulfur bacteria, but at the highly oxygenated surface, aerobic anoxygenic phototrophs (AAP) were numerically dominant (up to 16-36% of cultivable bacteria). Strains (EG8, EG13, EG17, EG19) with unusual phylogenetic affiliation and novel photosynthetic and metal(loid) reducing traits were described taxonomically. Chromocurvus halotolerans gen. nov., sp. nov. was proposed as a second example of a gammaproteobacterial AAP. It exhibited bent rod-shaped cells, unusual among AAP. Facultatively anaerobic Charonomicrobium ambiphototrophicum gen. nov., sp. nov. was capable of both aerobic and anaerobic anoxygenic photosynthesis, and incapable of photoautotrophy, distinguishing it from both AAP and purple nonsulfur bacteria. Roseovarius vanadiphilum sp. nov. surprisingly produced 4.5 times more biomass and 2 times more bacteriochlorophyll (BChl) at extremely high NaVO3 concentration (7.5 g/l) than in metal-free medium. A second novel metabolic mode, anaerobic respiration on the toxic metalloid tellurate, was described for a relative of non-phototrophic Shewanella frigidimarina (ER-Te-48), from deep ocean hydrothermal vent Paralvinella worms at Explorer Ridge in the Pacific Ocean. Other strains respired on SeO32- (ER-Se-17L), VO3- (ER-V-6), and VO43- (AV-V-25). These organisms provided the first examples of anaerobic respiration on Te, Se and V at hydrothermal vents. High level resistance of AAP to metal(loid)s prompted investigation of the influence of TeO32- on photosynthetic pigment production in species including Erythromicrobium ramosum (from a terrestrial hydrothermal system) and Erythrobacter litoralis (from a hypersaline supralittoral system). Tellurite enhanced photosynthetic pigment production up to 3.4 times, consistent with an antioxidant carotenoid-based defense mechanism. However, in E. litoralis BChl precursors such as Mg protoporphyrin or its monomethyl ester also accumulated, indicating biosynthetic pathway interruption. In hydrothermal and hypersaline ecosystems, largely devoid of eukaryotic phototrophs but often enriched in metal(loid)s, AAP and metal(loid) reducers are key modulators of nutrient and toxin availability. The presented results on their ecology, physiology and biochemistry have important implications for theoretical understanding of extreme environments and hold potential for biotechnological applications.

Artificial photosynthesis is often considered to have great potential to provide alternative, renewable fuels by harvesting, conversion and storage of solar energy. One promising approach is the development of modular molecular photocatalysts inspired by natural photosynthetic enzymes. The first part of this thesis deals with artificial mimics of the water oxidizing photosystem II composed of a chromophore and an electron relay as synthetic counterpart of the P680-TyrZ/His190 ensemble of photosystem II. Three ruthenium polypyridyl - imidazole - phenol complexes with varying position of a methyl group on the phenol ring (Ru-xMe) were synthesized and characterized by electrochemical and photophysical methods. As an improvement compared to earlier complexes the increased redox potential (~0.9 V vs. Ferrocene) of the phenol groups makes their function as an electron relay in a photocatalytic system for water oxidation thermodynamically possible. Time-resolved absorption studies revealed fast intramolecular electron transfer (<5-10 µs in aprotic solvent and <100 ns in water) despite the low driving force and the importance of the hydrogen bond between the phenol and the imidazole group was put in evidence. Slight differences between the three Ru-xMe complexes and investigation of the effect of external bases allowed to derive a mechanistic picture in which the imidazole is involved in a "proton domino" reaction. Accepting the phenolic proton upon ligand oxidation (within the H-bond) renders its second nitrogen site more acidic and only deprotonation of this site pulls the overall equilibrium completely towards oxidation of the ligand. Another part of this thesis comprises a chromophore-tryptophan construct synthesized using a click chemistry approach. Light-induced oxidation of Trp in this Ru-tryptophan complex was shown to follow ETPT mechanism. Depending on the pH conditions tryptophan radicals, either Trp* or TrpH*⁺ were detected and spectral measurement at different time showed the transition between the two forms. Deprotonation of the radical was dependent on the concentration of water as proton acceptor. Later part of the thesis deals with efforts to covalently bind a catalytic unit to the previously characterized chromophore-electron relay module. The click chemistry approach was not successful to obtain the final photocatalytic assembly. Therefore bimolecular activation of a Mn salen catalyst was performed and formation of Mn(IV) species was observed. As a step towards utilization of these types of photocatalysts in a photoelectrochemical cell a [Ru(bpy)₃]²⁺ chromophore with phosphonate anchoring groups (Ru-Phosphonate) was synthesized and grafted on the surface of a TiO₂ mesoporous semiconductor surface anode to perform photocurrent measurements.