Evandro Nascimento Silva

Photosynthetic changes and protective mechanisms against oxidative damage subjected to isolated and combined drought and heat stresses in Jatropha curcas plants

Photosynthetic changes and protective mechanisms against oxidative damage were evaluated in Jatropha curcas leaves subjected to drought and heat stresses, both individually and combined, in order to elucidate the synergistic and antagonistic mechanisms involved with these abiotic factors. Both the drought and heat stresses caused significant damage to the leaf membrane integrity and lipid peroxidation, and the combination of these stresses greatly enhanced these physiological disturbances. The leaf CO(2) assimilation rate, stomatal conductance and instantaneous carboxylation efficiency (P(N)/C(I)) were significantly decreased in all plants subjected to stressful conditions in comparison to unstressed plants (reference). In contrast, a reduction in photochemical activity was observed only in plants exposed to drought and drought+heat conditions. Catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities were stimulated only under heat stress, whereas APX activity was increased in all treated plants in comparison to the references. Moreover, the leaf H(2)O(2) content was increased similarly under all studied stresses. However, the balance of reduced and oxidized ascorbate did not show significant differences between reference and stressed plants. Although J. curcas plants acclimated to the studied stresses, they did not present an efficient mechanism for protection against drought-induced oxidative stress, especially when at high temperatures. However, heat-treated plants triggered an efficient enzymatic antioxidant system of reactive oxygen species scavenging and an effective protection against photochemical damages. The combination of drought and heat most significantly impaired the photosynthetic assimilation of CO(2) and the photochemical activity. These results indicate that drought greatly disturbs photosystem II activity and oxidative metabolism and that these negative effects are strongly stimulated by heat stress. The data also evidence that the combination of heat and drought triggers an intricate response involving antagonistic and synergistic interactions.

Salt stress induced damages on the photosynthesis of physic nut young plants

A salinidade e um dos principais fatores que limitam a produtividade das culturas no mundo principalmente em regioes semiaridas. Avaliou-se a resistencia da fotossintese de plantas jovens de pinhaomanso (Jatropha curcas L.) submetidas ao estresse salino. O experimento foi realizado em delineamento inteiramente casualizado com tratamentos em fatorial 2 x 3: duas concentracoes de NaCl (0 e 100 mmol L-1) e tres tempos de avaliacao (7 e 14 dias de exposicao e tres dias de recuperacao). As concentracoes de Na+ e Cl- e a relacao K+/Na+ nas folhas, apos sete dias de exposicao ao sal, nao indicaram niveis toxicos, sugerindo os efeitos osmoticos induzidos pelo NaCl prevaleceram sobre as causas ionicas. Sob essas condicoes, o estresse salino causou reducao nos parâmetros de trocas gasosas, como fixacao de CO2, condutância estomatica e transpiracao, mas ao contrario, nao alterou a eficiencia fotoquimica do fotossistema II. Apos 14 dias de tratamento, os ions salinos atingiram concentracoes muito elevadas nas folhas, provavelmente atingindo niveis toxicos. Em tais condicoes, as trocas gasosas e a atividade fotoquimica sofreram forte reducao causada pelo estresse ionico. O tratamento de recuperacao nao induziu queda intensa nas concentracoes dos ions salinos nas folhas e nenhuma melhoria foi observada no desempenho fotossintetico. Plantas jovens de pinhao manso sao sensiveis a condicoes de salinidade elevada por NaCl, mostrando altas concentracoes de Na+ e Cl-, baixa razao K+/Na+ e danos fotossinteticos intensos causados tanto por limitacoes estomaticas como por limitacoes bioquimicas.

Exogenous ornithine is an effective precursor and the δ-ornithine amino transferase pathway contributes to proline accumulation under high N recycling in salt-stressed cashew leaves

The role of the δ-ornithine amino transferase (OAT) pathway in proline synthesis is still controversial and was assessed in leaves of cashew plants subjected to salinity. The activities of enzymes and the concentrations of metabolites involved in proline synthesis were examined in parallel with the capacity of exogenous ornithine and glutamate to induce proline accumulation. Proline accumulation was best correlated with OAT activity, which increased 4-fold and was paralleled by NADH oxidation coupled to the activities of OAT and Δ(1)-pyrroline-5-carboxylate reductase (P5CR), demonstrating the potential of proline synthesis via OAT/P5C. Overall, the activities of GS, GOGAT and aminating GDH remained practically unchanged under salinity. The activity of P5CR did not respond to NaCl whereas Δ(1)-pyrroline-5-carboxylate dehydrogenase was sharply repressed by salinity. We suggest that if the export of P5C from the mitochondria to the cytosol is possible, its subsequent conversion to proline by P5CR may be important. In a time-course experiment, proline accumulation was associated with disturbances in amino acid metabolism as indicated by large increases in the concentrations of ammonia, free amino acids, glutamine, arginine and ornithine. Conversely, glutamate concentrations increased moderately and only within the first 24h. Exogenous feeding of ornithine as a precursor was very effective in inducing proline accumulation in intact plants and leaf discs, in which proline concentrations were several times higher than glutamate-fed or salt-treated plants. Our data suggest that proline accumulation might be a consequence of salt-induced increase in N recycling, resulting in increased levels of ornithine and other metabolites involved with proline synthesis and OAT activity. Under these metabolic circumstances the OAT pathway might contribute significantly to proline accumulation in salt-stressed cashew leaves.

Partial oxidative protection by enzymatic and non-enzymatic components in cashew leaves under high salinity

The work evaluated the role of enzymatic and non-enzymatic antioxidants in cashew (Anacardium occidentale) leaves under 0, 50, 100, 150 and 200 mM NaCl. Salt stress increased protein oxidation and decreased the lipid peroxidation, indicating that lipids are less susceptible to oxidative damage. The superoxide dismutase (SOD) activity was not changed, ascorbate peroxidase (APX) activity steadily decreased while the catalase (CAT) activity strongly increased with the increasing NaCl concentration. High salinity also induced alterations in the ascorbate (AsA) and glutathione (GSH) redox state. The salt resistance in cashew may be associated with maintaining of SOD activity and upregulation of CAT activity in concert with the AsA and GSH antioxidants.

Transporte e distribuição de potássio atenuam os efeitos tóxicos do sódio em plantas jovens de pinhão-manso

A number of studies have pointed out how potassium can alleviate the effects of sodium toxicity on plants. However, the mechanisms of interaction between these two ions at the whole plant level are poorly understood so far. This study assessed some physiological mechanisms involved with the K-Na interaction in Jatropha curcas seedlings exposed to salinity. The experiment was carried out in a completely randomized, 2 × 2 factorial design (two Na and K levels in nutrient solution, with five replications). The plants were exposed to the following treatments: K0Na0 (absence of both Na and K), K0Na1 (0 mmol L-1 K and 50 mmol L-1 Na), K1Na0 (10 mmol L-1 K and 0 mmol L-1 Na) and K1Na1 (10 mmol L-1 K and 50 mmol L-1 Na). After the test period, the results showed a strong antagonistic interaction in terms of K and Na transport rates in roots, stems and leaves. Without [K]ext in the nutrient solution, the Na transport rate in physic nut leaves was high, contributing to an excessive accumulation of this ion in the shoot and inducing toxicity symptoms in leaves. Conversely, the presence of adequate K evels alleviated the excessive accumulation of sodium in various plant parts, causing a decrease in the xylem Na flux rate. These data suggest that [K]ext can mitigate the adverse effects of sodium excess and reduce sodium contents in Jatropha curcas tissues.

Nitrate uptake, xylem NO3- flux, and nitrate assimilation in cowpea exposed to salinity.

This work was carried out to evaluate what is the nitrate acquisition stage (nitrate uptake, xylem nitrate flux or assimilatory reduction) most influenced by the presence of NaCl in cowpea. Twelve day-old seedlings were treated with 50 mM of NaCl in nutrient solution during four days and measurements carried out under two contrasting environmental conditions: typical day (full sun) and completely cloudy day (cloudiness). The salinity affected more intensely the xylem sap flux and nitrate flux than transpiration. Plants treated with NaCl showed a strong decrease in both nitrate uptake rate and leaf nitrate reductase activity as in the full sun as in cloudy day. Transpiration was reduced by the cloudiness while xylem sap flux and nitrate flux remained unchanged, in both salt-treated and control. Moreover, nitrate uptake and nitrate reductase activity were less affected by cloudiness than the transpiration. In addition, NaCl negatively affected nitrate accumulation in roots, stems and leaves while the cloudiness affected only the leaf nitrate accumulation, both in control and stressed plants. Salinity affects more negatively the nitrate xylem flux, as compared with the nitrate uptake and nitrate assimilatory reduction in cowpea leaves.

Salinity affects indirectly nitrate acquisition associated with glutamine accumulation in cowpea roots

The aim of this study was to test the hypothesis that salinity can affect indirectly the nitrate acquisition by a negative modulation triggered by glutamine accumulation. Cowpea plants were exposed to a mild NaCl concentration (50 mM) in order to restrict growth and N-demand. After 21 d, pretreated plants and control plants were supplied with 0, 5 and 10 mM of Ca(NO3)2 for 3 d in absence of NaCl. Salt pretreated plants showed a great limitation in acquisition of NO3−, indicated by decline in the nitrate uptake rate, NO3− accumulation, nitrate reductase activity and protein content. The restriction of NO3− utilization was positively associated with increased glutamine synthetase activity and glutamine accumulation, especially in roots.

Temperaturas elevadas afetam a distribuição de íons em plantas de feijão caupi pré-tratadas com NaCl1

The purpose of this study was to characterize the effect of temperature on the distribution of Na+, Cl- and K+ in roots, stems and leaves of cowpea pre-treated with NaCl. After the acclimation period, plants were divided into two groups: 0 NaCl and 100 mM NaCl for 2 days. Subsequently, the plants were divided into 4 sub-groups and subjected to increasing temperatures of 27, 32, 37 and 42 oC, separately, for a photoperiod of 12 hours at each temperature. The treatment without NaCl at 27 oC was used as reference. The concentrations of Na+ and Cl- in different organs were increased by pretreatment with NaCl and this accumulation was intensified by exposure to high temperatures. In roots, for example, at temperature of 42 oC concentrations of Na were four times higher than in leaves. While Cl- accumulated mainly in leaves, with a 20-fold increase in the concentration of this ion in relation to reference plants. Inversely, K+ concentrations were reduced in all organs analyzed. Thus, it is conclude that high temperatures affect the distribution of ions in different organs directly affecting ion homeostasis in plants.

Salt-induced NO3 - uptake inhibition in cowpea roots is dependent on the ionic composition of the salt and its osmotic effect

Salinity remarkably inhibits NO3- uptake but the mechanisms are not well understood. This study was addressed to elucidate the role of ionic and osmotic components of salinity on NO3- influx and efflux employing classic kinetics involving a low affinity transport system (LATS) and a high affinity transport system (HATS). In the presence of KCl, NaCl, and Na2SO4 at 100 mM concentrations, in both LATS and HATS, Michaelis constant (Km) was similar for the three salts and maximum rate (Vmax) decreased as follows: KCl > NaCl > Na2SO4, compared to control indicating a non-competitive interaction with NO3-. Unexpectedly, iso-osmotic solutions (osmotic potential Ψπ = -0.450) of polyethylene glycol (PEG, 17.84 %, v/v) and mannitol (100 mM) remarkably increased Km in both the LATS and the HATS, but Vmax did not change indicating a competitive inhibition. Under the PEG and mannitol treatments, Km and Vmax were higher than under the salt treatments. The salts increased slightly NO3- efflux in the following order KCl > NaCl > Na2SO4. In contrast, mannitol strongly stimulated and the PEG inhibited NO3- efflux. The obtained data reveal that salinity effects were not dependent on the anion type (Cl- versus SO42-) indicating a non-competitive inhibition mechanism between Cl- and NO3-. In contrast, the cation types (K+versus Na+) had a pronounced effect. The osmotic component is important to net NO3- uptake affecting remarkably the influx in both LATS and HATS components of cowpea roots.

Physiological Mechanisms Involved with Salt and Drought Tolerance in Jatropha curcas Plants

Although the importance ofJ. curcasplants as a bioenergy source is well recognized, the key physiological processes involved in drought and salt tolerance are poorly known. The geographical distribution ofJ. curcasstrongly suggests that this species is drought tolerant. However, the features of the physiological parameters of drought tolerance were based, until now, on a narrow genetic basis that was not well characterized. In the tropical, semi-arid regions where the cultivation ofJ. curcasis increasing, problems of primary salinity and secondary salinization caused by irrigation can be critical. In this review, we present recent results regarding the most important physiological processes related to drought and salt tolerance inJ. curcas,including osmotic adjustment, photosynthesis and oxidative protection. Overall, the data reported suggest thatJ. curcashas both biochemical and physiological characteristics that confer drought tolerance and relative salt sensitivity during its initial growth phase. The possibility of sustainable production ofJ. curcaswithout irrigation in semiarid regions is controversial, partly because the physiology of this species is not yet sufficiently known and the plant breeding has presented little progress. In addition, the development of “evergreen crops” with irrigation also requires physiological studies and genotypes that respond adequately to water investment under adverse conditions of high temperature and salinity.