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Efficient plant acclimation to changing environmental conditions relies on fast adjustments of the transcriptome, proteome, and metabolome. Regulation of enzyme activity depends on the activity of specific chaperones, chemical post-translational modifications (PTMs) of amino acid residues, and changes in the cellular and organellar microenvironment. Central to carbon assimilation, and thus plant growth and yield, Rubisco activity is regulated by its chaperone Rubisco activase (Rca) and by adjustments in the chloroplast stroma environment. Focused on crops, this review highlights the main PTMs and stromal ions and metabolites affecting Rubisco and Rca in response to environmental stimuli. Rca isoforms differ in regulatory properties and heat sensitivity, with expression changing according to the surrounding environment. Much of the physiological relevance of Rubisco and Rca PTMs is still poorly understood, though some PTMs have been associated with Rubisco regulation in response to stress. Ion and metabolite concentrations in the chloroplast change in response to variations in light and temperature. Some of these changes promote Rubisco activation while others inhibit activation, deactivate the enzyme, or change the rates of catalysis. Understanding these regulatory mechanisms will aid the development of strategies to improve carbon fixation by Rubisco under rapidly changing environments as experienced by crop plants.

This dissertation explores the fundamental dynamics that control atmospheric and ocean circulation on water worlds. These planets are defined by the presence of liquid water, which is a minimum requirement for life as we know it, making them compelling targets in the search for extraterrestrial life. This work begins by examining the atmospheric features and surface climates of Earth-like planets with surface liquid water (Chapters I-III). These atmospheres are driven by top-of-atmosphere radiative imbalance. To further our understanding of planetary climate and of the atmosphere’s dynamical controls, particularly with regards to seasonal behavior, we examine the circulation, energy budget, and hydrological cycle responses to changes in shortwave and longwave radiative forcings. This dissertation also explores icy worlds (Chapters IV-V), a type of water world where a liquid water ocean hides beneath a substantial icy shell. Processes occurring at the ocean boundaries can shape the circulation dynamics, stratification, and subsequent heat and salt distributions in the ocean interior. This work presents a new model for exploring these oceans, focusing on ocean-ice interactions and freshwater forcings on Enceladus.

The physiological mechanisms responsible for salinity tolerance in Rhizophora mangle remain unclear. Moreover, the effects of climate change on the distribution and abundance of mangrove forests are unknown. Thus, to elucidate the possible factors responsible for saline tolerance in this species, we investigated the growth and physiological parameters in young plants cultivated in a saline gradient (0, 10, 35, and 70 ppt). Biometric indicators, water status parameters, cell integrity, ions concentrations in leaves and roots, pigment concentrations, chlorophyll a fluorescence, oxidative stress indicators, and antioxidant enzyme activities were evaluated. The results showed that R. mangle could grow in the absence (0 ppt) or moderate salinity (10 ppt). However, by increasing the salinity to sea level (35 ppt), the growth and development decreased compared to plants grown at ten ppt. In hypersalinity (70 ppt), plant growth and development are severely hampered. Under hypersalinity, the increased concentration of H2O2 promoted lipid peroxidation and membrane damage. The chlorophyll contents decreased, and accessory pigment concentrations increased. Moreover, the modulation of the quantum yield of PSII and the antioxidant system was crucial to avoiding photoinhibition and salinity tolerance in R. mangle.

In this study we use idealized aquaplanet simulations of Earth-like planets to explore the large-scale atmospheric circulation’s response to changes in shortwave radiation, through changes in the planet obliquity, and in longwave radiation, through changes in the prescribed optical depth. We primarily focus on the extratropical circulation and the counter-intuitive weakening of extratropical eddy activity, and associated precipitating storm tracks, with increased obliquity. We show that on high obliquity planets with a small surface thermal inertia, net energy deficit during the winter months is primarily balanced by the latent energy component of the atmospheric heat capacity, which buffers any significant atmospheric cooling. As temperatures finally start to decrease, condensational latent heat release of atmospheric moisture further slows down the cooling and keeps the winter pole warmer than the mid latitudes until after the winter solstice. This prevents vigorous baroclinic eddy activity, which lives off the potential energy stored in the sloping isopycnals, as well as the development of a Ferrel cell and storm track. For planets with larger surface heat capacity, we see a similar suppression, with the energy storage in the ocean surface, rather than atmospheric latent energy storage, primarily balancing the net energy loss during the winter months. These results suggest that, regardless of surface thermal inertia, water-covered high obliquity Earth-like planets would not experience significant extratropical storm activity and highlight the need for a proper characterization of polar properties in planetary modeling and observational investigations.

Climate change is mainly driven by the accumulation of carbon dioxide (CO2) in the atmosphere in the last century. Plant growth is constantly challenged by environmental fluctuations including heat waves, severe drought and salinity, along with ozone accumulation in the atmosphere. Food security is at risk in an increasing world population, and it is necessary to face the current and the expected effects of global warming. The effects of the predicted environment scenario of elevated CO2 concentration (e[CO2]) and more severe abiotic stresses have been scarcely investigated in woody plants, and an integrated view involving physiological, biochemical and molecular data is missing. This review highlights the effects of elevated CO2 in the metabolism of woody plants and the main findings of its interaction with abiotic stresses, including a molecular point of view, aiming to improve the understanding of how woody plants will face the predicted environmental conditions. Overall, e[CO2] stimulates photosynthesis and growth and attenuates mild to moderate abiotic stress in woody plants if root growth and nutrients are not limited. Moreover, e[CO2] does not induce acclimation in most tree species. Some high-throughput analyses involving omics techniques were conducted to better understand how these processes are regulated. Finally, knowledge gaps in the understanding of how the predicted climate condition will affect woody plant metabolism were identified, with the aim of improving the growth and production of this plant species.

Rocky planets orbiting M-dwarf stars are among the most promising and abundant astronomical targets for detecting habitable climates. Planets in the M-dwarf habitable zone are likely synchronously rotating, such that we expect significant day-night temperature differences, and potentially limited fractional habitability. Previous studies have focused on scenarios where fractional habitability is confined to the substellar or "eye" region, but in this paper we explore the possibility of planets with terminator habitability, defined by the existence of a habitable band at the transition between a scorching dayside and a glacial nightside. Using a global climate model, we show that for water-limited planets it is possible to have scorching temperatures in the "eye" and freezing temperatures on the nightside, while maintaining a temperate climate in the terminator region, due to a reduced atmospheric energy transport. Whereas on water-rich planets, increasing stellar flux leads to increased atmospheric energy transport and a reduction in day-night temperature differences, such that the terminator does not remain habitable once the dayside temperatures approach runaway or moist greenhouse limits. We also show that, while water-abundant simulations may result in larger fractional habitability, they are vulnerable to water loss through cold-trapping on the nightside surface or atmospheric water vapor escape, suggesting that even if planets were formed with abundant water, their climates could become water-limited and subject to terminator habitability., Comment: 16 pages, 9 figures, 3 tables, Accepted for publication in The Astronomical Journal

Increasing atmospheric [CO 2] is thought to contribute to changes in precipitation patterns, increasing heatwaves and severe drought scenarios. However, how the combination of elevated [CO 2] and progressive drought affect plant metabolism is poorly understood. Aiming to investigate the effects of this environmental condition on photosynthesis and specialized metabolites in leaves of Coffea arabica during the early growth, plants fertilized with ambient (a[CO 2]-400 ppm) and elevated (e[CO 2]-800 ppm) [CO 2] were exposed to well-watered (WW) or water-deficit (WD) regimes for 40 days. Over the 40-day-water-withdrawal, soil moisture, and leaf water potential decreased compared to WW-condition. Elevated [CO 2] stimulates CO 2 assimilation (A) and intrinsic water use efficiency (iWUE) even under WD. Drought condition slightly changed stomatal conductance, transpiration rate and maximum quantum efficiency of photosystem II (PSII) regardless of [CO 2] compared to WW-plants. Total soluble amino acid concentration did not change significantly, while total phenolic compounds concentration decreased under e[CO 2] regardless of water regimes. The combination of e[CO 2]+WD increased the 5-O-caffeoylquinic acid (5-CQA) and caffeine amounts by 40-day when compared to a[CO 2]+WD plants. Altogether, these results suggest that e[CO 2] buffers mild-drought stress in young C. arabica by increasing A, iWUE and stimulating changes in the leaf contents of 5-CQA and caffeine.

Enceladus is believed to have a saltwater global ocean with a mean depth of at least 30~km, heated from below at the ocean-core interface and cooled at the top, where the ocean loses heat to the icy lithosphere above. This scenario suggests an important role for vertical convection to influence the interior properties and circulation of Enceladus' ocean. Additionally, the ice shell that encompasses the ocean has dramatic meridional thickness variations that, in steady state, must be sustained against processes acting to remove these ice thickness anomalies. One mechanism that would maintain variations in the ice shell thickness involves spatially-separated regions of freezing and melting at the ocean-ice interface. Here, we use an idealized, dynamical ocean model forced by an observationally-guided density forcing at the ocean-ice interface to argue that Enceladus' interior ocean should support a meridional overturning circulation. This circulation establishes an interior density structure that is more complex than in studies that have focused only on convection, including a shallow freshwater lens in the polar regions. Spatially-separated sites of ice formation and melt enable Enceladus to sustain a significant vertical and horizontal stratification, which impacts interior heat transport, and is critical for understanding the relationship between a global ocean and the planetary energy budget. The presence of low salinity layers near the polar ocean-ice interface also influences whether samples measured from the plumes are representative of the global ocean.

Ongoing discoveries of terrestrial exoplanets and the desire to determine their habitability have created an increasing demand for studies of a wide range of climatic regimes and atmospheric circulations. These studies have, in turn, challenged our understanding of our own planet’s atmospheric dynamics and provided new frameworks with which we can further our understanding of planetary atmospheres. In this work, we use an idealized moist general circulation model in aquaplanet configuration to study the atmospheric circulation of terrestrial planets with high obliquities. With seasonally varying insolation forcing and a shallow slab ocean as a lower boundary, we emphasize seasonal phenomena that might not be captured in simulations with annual mean forcing and that might involve nonlinear behaviors. By progressively increasing obliquity, we explore the response of the large-scale atmospheric circulation to more extreme seasonal cycles and a reversed annual mean equator-to-pole insolation distribution, and its impact on the energy and water cycles. We show that for high obliquities, the large-scale atmospheric circulation and the meridional energy transport are dominated by seasonally reversing broad cross-equatorial Hadley cells that transport energy from the summer to the winter hemisphere and significantly mitigate temperature extremes. These overturning cells also play a major role in shaping the planet’s hydrological cycle, with the associated ascending branches and precipitation convergence zones becoming progressively broader and more poleward shifted into the summer hemisphere with higher obliquities. While not embedded within the Hadley cell ascending branches, the hot summer poles of high obliquity planets experience nonnegligible precipitation during and at the end of the warm season: during the summer, lower-level moist static energy maxima at the summer poles force locally enhanced convective activity. As temperatures rapidly drop at the end of the summe

Photosynthesis involves the conversion of sunlight energy into stored chemical energy, which is achieved through electron transport along a series of redox reactions. Excess photosynthetic electron transport might be dangerous due to the risk of molecular oxygen reduction, generating reactive oxygen species (ROS) over-accumulation. Avoiding excess ROS production requires the rate of electron transport to be coordinated with the capacity of electron acceptors in the chloroplast stroma. Imbalance between the donor and acceptor sides of photosystem I (PSI) can lead to inactivation, which is called PSI photoinhibition. We used a light-inducible PSI photoinhibition system in Arabidopsis thaliana to resolve the time dynamics of inhibition and to investigate its impact on ROS production and turnover. The oxidation state of the PSI reaction center and rates of CO 2 fixation both indicated strong and rapid PSI photoinhibition upon donor side/acceptor side imbalance, while the rate of inhibition eased during prolonged imbalance. PSI photoinhibition was not associated with any major changes in ROS accumulation or antioxidant activity; however, a lower level of lipid oxidation correlated with lower abundance of chloroplast lipoxygenase in PSI-inhibited leaves. The results of this study suggest that rapid activation of PSI photoinhibition under severe photosynthetic imbalance protects the chloroplast from over-reduction and excess ROS formation.

In nature, plants are simultaneously challenged by biotic and abiotic stresses. However, little is known about the effects of these combined stresses for most crops. This work aimed to evaluate the responsed of the virus-resistant cowpea genotype BRS-Marataoã to the exposure of salt stress combined with CPSMV infection. Cowpea plants were exposed to 200 mM NaCl either simultaneously (SV plant group) or 24 h prior to the CPSMV infection [S(24 h)V plant group]. Physiological, biochemical, and proteomic analyses at 2 and 6 days post salt stress (DPS) revealed that cowpea significantly reprogrammed its cellular metabolism. Indeed, plant size, photosynthetic parameters (net photosynthesis, transpiration rate, stomatal conductance, and internal CO 2 partial pressure) and chlorophyll and carotenoid contents were reduced in S(24 h)V compared to SV. Moreover, accumulation of viral particles at 6 DPS in S(24 h)V was observed indicating that the salt stress imposed prior to virus infection favors viral particle proliferation. Proteomic analysis showed differential contents of 403 and 330 proteins at 2 DPS and 6 DPS, respectively, out of 733 differentially abundant proteins between the two plant groups. The altered leaf proteins are involved in energy and metabolism, photosynthesis, stress response, and oxidative burst. Biological significance: This is an original study in which a virus-resistant cowpea genotype (BRS-Marataoã) was (i) exposed simultaneously to 200 mM NaCl and inoculation with CPSMV (SV plant group) or (ii) exposed to 200 mM NaCl stress 24 h prior to inoculation with CPSMV [S(24 h)V plant group]. The purpose was to shed light on how this CPSMV resistant cowpea responded to the combined stresses. Numerous key proteins and associated pathways were altered in the cowpea plants challenged with both stresses, but unexpectedly, the salt stress imposed 24 h prior to CPSMV inoculation allowed viral proliferation, turning the cowpea genotype from resistant to susceptible

Mechanisms involving ammonium toxicity, excess light, and photosynthesis are scarcely known in plants. We tested the hypothesis that high NH 4 + supply in presence of high light decreases photosynthetic efficiency of rice plants, an allegedly tolerant species. Mature rice plants were previously supplied with 10 mM NH 4 + or 10 mM NO 3 − and subsequently exposed to 400 µmol m −2 s −1 (moderate light—ML) or 2000 µmol m −2 s −1 (high light—HL) for 8 h. HL greatly stimulated NH 4 + accumulation in roots and in a minor extent in leaves. These plants displayed significant delay in D1 protein recovery in the dark, compared to nitrate-supplied plants. These responses were related to reduction of both PSII and PSI quantum efficiencies and induction of non-photochemical quenching. These changes were also associated with higher limitation in the donor side and lower restriction in the acceptor side of PSI. This later response was closely related to prominent decrease in stomatal conductance and net CO 2 assimilation that could have strongly affected the energy balance in chloroplast, favoring ATP accumulation and NPQ induction. In parallel, NH 4 + induced a strong increase in the electron flux to photorespiration and, inversely, it decreased the flux to Rubisco carboxylation. Overall, ammonium supply negatively interacts with excess light, possibly by enhancing ammonium transport towards leaves, causing negative effects on some photosynthetic steps. We propose that high ammonium supply to rice combined with excess light is capable to induce strong delay in D1 protein turnover and restriction in stomatal conductance, which might have contributed to generalized disturbances on photosynthetic efficiency.

Rice is one of the world's most important crops and an excellent model system for understanding the interaction between genes and environmental changes. However, its productivity is often challenged by abiotic stresses, which results in the accumulation of reactive oxygen species. Glutathione peroxidases are part of the mechanism by which plants face oxidative stress. These enzymes can control redox homeostasis and also play a role in redox signaling. Here, we investigate the role of rice GPX3 in plant responses to salt stress using OsGPX3-RNAi silenced rice plants (GPX3s). Our results indicate that GPX3s plants are more sensitive to salinity showing decreased biomass, CO 2 assimilation rate, stomatal conductance, and intercellular CO 2 partial pressure. Moreover, these plants present significant damage to photosystem II activity and decline in chlorophyll content. Salt stress induced ROS accumulation in both non-transformed (NT) and GPX3s plants, indicating that GPX3s sensibility to salt stress was not due to the significant impairment in redox equilibrium. Together, these results show GPX3 importance in rice to achieve salt stress tolerance via an independent ROS-scavenger mechanism. Moreover, it also provides new light into the cross-talk between chloroplasts and mitochondria, suggesting a novel role to this enzyme beyond its role as ROS-scavenger.

Rubisco catalyzes the fixation of CO 2 into organic compounds that are used for plant growth and the production of agricultural products, and specific sugar-phosphate derivatives bind tightly to the active sites of Rubisco, locking the enzyme in a catalytically inactive conformation. 2-carboxy-d-arabinitol-1-phosphate phosphatase (CA1Pase) dephosphorylates such tight-binding inhibitors, contributing to the maintenance of Rubisco activity. Here, we investigated the hypothesis that overexpressing ca1pase would decrease the abundance of Rubisco inhibitors, thereby increasing the activity of Rubisco and enhancing photosynthetic performance and productivity in wheat ( Triticum aestivum). Plants of four independent wheat transgenic lines overexpressing ca1pase showed up to 30-fold increases in ca1pase expression compared to the wild type. Plants overexpressing ca1pase had lower numbers of Rubisco tight-binding inhibitors and higher Rubisco activation state than the wild type; however, there were 17% to 60% fewer Rubisco active sites in the four transgenic lines than in the wild type. The lower Rubisco content in plants overexpressing ca1pase resulted in lower initial and total carboxylating activities measured in flag leaves at the end of the vegetative stage and lower aboveground biomass and grain yield measured in fully mature plants. Hence, contrary to what would be expected, ca1pase overexpression decreased Rubisco content and compromised wheat grain yields. These results support a possible role for Rubisco inhibitors in protecting the enzyme and maintaining an adequate number of Rubisco active sites to support carboxylation rates in planta.

Introduction and objectives: Chronic total coronary occlusion (CTO) of coronary arteries is frequent in heart transplant recipients (HTR). It is usually managed with medical therapy due to the suboptimal results shown by the percutaneous coronary intervention (PCI). Although the PCI of native CTOs is performed in experienced centres, in HTR we do not know PCI results or clinical efficacy. This is the first study ever to actually analyse the PCI-Target Lesion Procedure Success of CTO PCI and its angiographic and clinical follow-up in HTR. In addition, we compared the clinical follow-up of CTO vs non-CTO PCI in HTR. Methods: We retrospectively analysed the baseline characteristics, procedural outcomes and clinical events during the follow-up of HTR with CTO undergoing PCI between January 1, 2006 and December 31, 2016 in 2 centres with an ongoing CTO program. Over the same period, we also compared clinical events during the follow-up of these patients vs PCI on non-CTO stenosis in HTR at one of the centres. Results: PCI was successful in 13 out of 14 patients. A systematic follow-up angiography was conducted at centre 1 (n = 10). Two patients showed in-stent restenosis (20%), and a new PCI was performed successfully in both cases. Mortality rate was 28.5%, after a median follow-up of 33.5 months [interquartile range, 20-50]. We found no statistical differences in the clinical events after the PCI of CTO lesions vs non-CTO lesions in HTR. Conclusions: The PCI of CTO in HTR is feasible in experienced centres and selected patients, with a high success rate and low rate of intraprocedural complications., Introducción y objetivos: Las oclusiones coronarias crónicas totales (OTC) son frecuentes en los pacientes receptores de trasplante cardiaco (PTC) y suelen tratarse con tratamiento médico debido a los resultados subóptimos de la intervención coronaria percutánea (ICP). A pesar de que la ICP de OTC en corazones nativos se lleva a cabo en centros experimentados, no se conocen sus resultados ni la eficacia clínica en PTC. Este es el primer estudio que analiza la tasa de éxito de la ICP sobre OTC en PTC, así como el seguimiento clínico y angiográfico. Así mismo, se comparan los eventos clínicos durante el seguimiento de los PTC tratados con ICP sobre OTC frente a PTC con ICP sobre estenosis no oclusivas. Métodos: Se analizaron retrospectivamente las características clínicas basales, los resultados del procedimiento y los eventos clínicos durante el seguimiento de los PTC con OTC en quienes se realizó una ICP entre el 1 de enero de 2006 y el 31 de diciembre de 2016 en 2 centros con un programa específico de OTC. Además, se compararon los eventos clínicos durante el seguimiento de estos pacientes con los de PTC tratados con ICP sobre una estenosis coronaria no oclusiva en uno de los centros durante el mismo periodo de tiempo. Resultados: La ICP resultó exitosa en 13 de los 14 pacientes. Se realizó un seguimiento angiográfico sistemático en el centro 1 (n = 10). Dos pacientes presentaron reestenosis en el interior del stent (20%), por lo que se realizó una nueva ICP sobre ellas que tuvo éxito en ambos casos. La mortalidad fue del 28,5% con una mediana de seguimiento de 33,5 meses [rango intercuartílico, 20-50]. No se encontraron diferencias estadísticamente significativas entre los eventos clínicos tras la ICP sobre una OTC y tras la ICP sobre una estenosis no oclusiva en PTC. Conclusiones: La ICP sobre OTC en PTC es factible en centros con experiencia y en pacientes seleccionados, con una alta tasa de éxito y una baja frecuencia de complicaciones periprocedimiento.

Aims: Understanding mechanisms underlying N use efficiency (NUE) after luxury consumption and nitrate deprivation is crucial to crop productivity. The aim was to elucidate the importance of photosynthesis, assimilatory nitrate reduction and N-reserve remobilization to NUE in cotton. Methods: Plants were exposed to three conditions in nutrient solution: (a) previous exposure to high nitrate supply (10 mM) for long-term (8 days); (b) nitrate deprivation (NO 3 − withdrawal) for 8 days followed by (c) an early N-deficiency for 4 days. Results: Plants supplied with nitrate excess were able to display increment in shoot NUE related to dry matter gain, whereas photosynthetic N use efficiency did not change, evidencing that excess N per se was not able to improve CO 2 assimilation. Nitrate reductase (NR) activity was crucial to remobilize stored nitrate through deprivation phase and free amino acids, total proteins, and chlorophylls were also essential to N-remobilization. High NUE was important to kept high root growth rates throughout deprivation and early deficiency phases. Despite the great decrease in chlorophyll content, PSII and PSI activities were kept stable until the onset of early N-deficiency, when cotton plants displayed high shoot NUE. Conclusions: These responses are closely associated with high NR activity and sustaining of photosynthesis, which contribute to N-homeostasis in different nutritional regimes.

Primary adrenal insufficiency, a rare disease in pediatric population, has different etiologies that determine treatment and prognosis. Clinical manifestations can be insidious and subtle, delaying the diagnosis. Hyperpigmentation is a characteristic sign of primary adrenal insufficiency and it can be the only manifestation. X-linked adrenoleukodystrophy is a peroxisomal disorder characterized by very long chain fatty acids accumulation in different organs, namely adrenal gland, leading to adrenal insufficiency. The authors report a 10 years-old boy who presented with behavioral changes, hyperactivity, poor school performance and hyperpigmentation. He was diagnosed to have primary adrenal insufficiency secondary to X-linked adrenoleukodystrophy. His diagnosis was delayed because of the initial vague symptoms. With this case the authors aim to increase the awareness to different clinical manifestations of primary adrenal insufficiency as well as create awareness that X-linked adrenoleukodystrophy is an important etiology of adrenal insufficiency in boys.

Spraying sucrose inhibits photosynthesis by impairing Rubisco activity and stomatal conductance (gs), whereas increasing sink demand by partially darkening the plant stimulates sugarcane photosynthesis. We hypothesized that the stimulatory effect of darkness can offset the inhibitory effect of exogenous sucrose on photosynthesis. Source-sink relationship was perturbed in two sugarcane cultivars by imposing partial darkness, spraying a sucrose solution (50 mM) and their combination. Five days after the onset of the treatments, the maximum Rubisco carboxylation rate (Vcmax) and the initial slope of A-Ci curve (k) were estimated by measuring leaf gas exchange and chlorophyll fluorescence. Photosynthesis was inhibited by sucrose spraying in both genotypes, through decreases in Vcmax, k, gs and ATP production driven by electron transport (Jatp). Photosynthesis of plants subjected to the combination of partial darkness and sucrose spraying was similar to photosynthesis of reference plants for both genotypes. Significant increases in Vcmax, gs and Jatp and marginal increases in k were noticed when combining partial darkness and sucrose spraying compared with sucrose spraying alone. Our data also revealed that increases in sink strength due to partial darkness offset the inhibition of sugarcane photosynthesis caused by sucrose spraying, enhancing the knowledge on endogenous regulation of sugarcane photosynthesis through the source-sink relationship.

Cowpea severe mosaic virus (CPSMV) causes significant losses in cowpea (Vigna unguiculata) production. In this present study biochemical, physiological, and proteomic analysis were done to identify pathways and defense proteins that are altered during the incompatible interaction between the cowpea genotype BRS-Marataoã and CPSMV. The leaf protein extracts from mock- (MI) and CPSMV-inoculated plantlets (V) were evaluated at 2 and 6 days post-inoculation (DPI). Data support the assumptions that increases in biochemical (high hydrogen peroxide, antioxidant enzymes, and secondary compounds) and physiological responses (high photosynthesis index and chlorophyll content), confirmed by label-free comparative proteomic approach, in which quantitative changes in proteasome proteins, proteins related to photosynthesis, redox homeostasis, regulation factors/RNA processing proteins were observed may be implicated in the resistance of BRS-Marataoã to CPSMV. This pioneering study provides information for the selection of specific pathways and proteins, altered in this incompatible relationship, which could be chosen as targets for detailed studies to advance our understanding of the molecular, physiological, and biochemistry basis of the resistance mechanism of cowpea and design approachs to engineer plants that are more productive.

Photosynthetic modulation by sugars has been known for many years, but the biochemical and molecular comprehension of this process is lacking. We studied how the exogenous sucrose supplied to leaves could affect sugar metabolism in leaf, sheath and stalk and inhibit photosynthesis in four-month old sugarcane plants. Exogenous sucrose 50 mM sprayed on attached leaves strongly impaired the net CO2 assimilation (PN) and decreased the instantaneous carboxylation efficiency (PN/Ci), suggesting that the impairment in photosynthesis was caused by biochemical restrictions. The photosystem II activity was also affected by excess sucrose as indicated by the reduction in the apparent electron transport rate, effective quantum yield and increase in non-photochemical quenching. In leaf segments, sucrose accumulation was related to increases in the activities of soluble acid and neutral invertases, sucrose synthase and sucrose phosphate synthase, whereas the contents of fructose increased and glucose slightly decreased. Changes in the activities of sucrose hydrolyzing and synthesizing enzymes in leaf, sheath and stalk and sugar profile in intact plants were not enough to identify which sugar(s) or enzyme(s) were directly involved in photosynthesis modulation. However, exogenous sucrose was able to trigger down-regulation in the Rubisco abundance, activation state and enzymatic activity. Despite the fact that PN/Ci had been notably decreased by sucrose, in vitro activity and abundance of PEPCase did not change, suggesting an in vivo modulation of this enzyme. The data reveal that sucrose and/or other derivative sugars in leaves inhibited sugarcane photosynthesis by down-regulation of Rubisco synthesis and activity. Our data also suggest that sugar modulation was not exerted by a feedback mechanism induced by the accumulation of sugars in immature sugarcane stalk.

The relationships between salt tolerance and photosynthetic mechanisms of excess energy dissipation were assessed using two species that exhibit contrasting responses to salinity, Ricinus communis (tolerant) and Jatropha curcas (sensitive). The salt tolerance of R. communis was indicated by unchanged electrolyte leakage (cellular integrity) and dry weight in leaves, whereas these parameters were greatly affected in J. curcas. The leaf Na+ content was similar in both species. Photosynthesis was intensely decreased in both species, but the reduction was more pronounced in J. curcas. In this species biochemical limitations in photosynthesis were more prominent, as indicated by increased Ci values and decreased Rubisco activity. Salinity decreased both the Vcmax (in vivo Rubisco activity) and Jmax (maximum electron transport rate) more significantly in J. curcas. The higher tolerance in R. communis was positively associated with higher photorespiratory activity, nitrate assimilation and higher cyclic electron flow. The high activity of these alternative electron sinks in R. communis was closely associated with a more efficient photoprotection mechanism. In conclusion, salt tolerance in R. communis, compared with J. curcas, is related to higher electron partitioning from the photosynthetic electron transport chain to alternative sinks.

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Languages and Linguistics, Arts, Education and Law, Concerns about student retention and attrition rates in higher education have been steadily increasing over the years. Efforts to identify and treat potential withdrawers have grown considerably; now, more than ever, universities are getting more competitive and financially driven, as the issue of student attrition is threatening to affect the way in which universities continue to run (Harvey, Drew & Smith, 2006). More universities are now developing strategic retention plans that aim at keeping students enrolled in their courses, as there is no doubt that as attrition rates increase, universities’ funding could be at risk (Schwartz, 2007). Literature on student attrition and retention in higher education shows that there has been a substantial amount of research conducted into the issues of attrition and retention in general. Varied conceptual models have been developed to explain and acknowledge student attrition as problematic and these models have focused on determining the factors contributing to student withdrawal, as well as the elements that contribute to student success. However, until now, the literature available shows that there seems to be a shortage of research into the area of foreign language student attrition and retention. As the number of students learning a foreign language in Australian high schools is at its lowest ever, this lack of research is worrying (Group of Eight, 2007). This ultimately illustrates the importance and significance of research studies conducted to determine the reasons why students are withdrawing from foreign language classes at tertiary institutions. This study investigates student attrition and develops a prognostic approach to identify students at risk of withdrawing from their courses. The study was divided into three stages. The first stage examined class assessment reports to provide a picture of existing attrition rates in the course being examined, Elementary Spanish. The second stage explored factors contributing

Concerns about student retention and attrition rates in higher education have been steadily increasing over the years. Efforts to identify and treat potential withdrawers have grown considerably; now, more than ever, universities are getting more competitive and financially driven, as the issue of student attrition is threatening to affect the way in which universities continue to run (Harvey, Drew & Smith, 2006). More universities are now developing strategic retention plans that aim at keeping students enrolled in their courses, as there is no doubt that as attrition rates increase, universities’ funding could be at risk (Schwartz, 2007). Literature on student attrition and retention in higher education shows that there has been a substantial amount of research conducted into the issues of attrition and retention in general. Varied conceptual models have been developed to explain and acknowledge student attrition as problematic and these models have focused on determining the factors contributing to student withdrawal, as well as the elements that contribute to student success. However, until now, the literature available shows that there seems to be a shortage of research into the area of foreign language student attrition and retention. As the number of students learning a foreign language in Australian high schools is at its lowest ever, this lack of research is worrying (Group of Eight, 2007). This ultimately illustrates the importance and significance of research studies conducted to determine the reasons why students are withdrawing from foreign language classes at tertiary institutions. This study investigates student attrition and develops a prognostic approach to identify students at risk of withdrawing from their courses. The study was divided into three stages. The first stage examined class assessment reports to provide a picture of existing attrition rates in the course being examined, Elementary Spanish. The second stage explored factors contributing, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Languages and Linguistics, Arts, Education and Law, Full Text