Sérgio Luiz Ferreira-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.

Cytosolic APx knockdown indicates an ambiguous redox responses in rice

Ascorbate peroxidases (APX, EC 1.1.11.1) are class I heme-peroxidases, which catalyze the conversion of H(2)O(2) into H(2)O, using ascorbate as a specific electron donor. Previously, the presence of eight Apx genes was identified in the nuclear genome of rice (Oryza sativa), encoding isoforms that are located in different sub-cellular compartments. Herein, the generation of rice transgenic plants silenced for either both or each one of the cytosolic Apx1 and Apx2 genes was carried out in order to investigate the importance of cytosolic Apx isoforms on plant development and on plant stress responses. Transgenic double Apx1/2-silenced plants exhibited normal development, even though these plants showed a global reduction of Apx activity which strongly impacts the whole antioxidant system regulation. Apx1/2-silenced plants also showed increased H(2)O(2) accumulation under control and stress situations and presented higher tolerance to toxic concentration of aluminum when compared to wild type plants. On the other hand, silencing OsApx1 and OsApx2 genes individually resulted in strong effect on plant development producing semi-dwarf phenotype. These results suggested that the double silencing of cytosolic OsApx genes induced compensatory antioxidant mechanisms in rice while single knockdown of these genes did not, which resulted in the impairing of normal plant development.

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.

Changes in physiological indicators associated with salt tolerance in two contrasting cashew rootstocks

L.) rootstocks in response to salt stress. The tolerant CCP 09 genotype showed better growthperformance after two weeks under a large range of NaCl salinity (50, 100, 150 and 200 mM). The NaCl treatments induceda significant drop in transpiration as a consequence of an increased stomatal resistance in both genotypes. Nosignificant differences in Na

Influência de porta-enxertos na resistência de mudas de cajueiro ao estresse salino

O objetivo deste trabalho foi avaliar a influencia de porta-enxertos na resistencia de mudas de cajueiro (Anacardium occidentale L.) a salinidade. As mudas foram obtidas pela enxertia do clone BRS 226 sobre os porta-enxertos CAPI 4, CCP 09 e BRS 226. Foram expostas a meio hidroponico sem NaCl (controle) ou com NaCl 200 mM (tratamento salino), sob condicoes controladas de temperatura, umidade e luminosidade, durante 12 dias. O delineamento foi o inteiramente casualizado, em esquema fatorial 3x2 (tres combinacoes de enxerto/porta-enxerto e duas concentracoes de NaCl), com quatro repeticoes. Foram determinados a concentracao de Na+, Cl-, K+ e solutos orgânicos e os sintomas visuais de toxicidade nas folhas. Os conteudos de Na+ e Cl-, a relacao K+/Na+ e as concentracoes de aminoacidos e de prolina livres nas folhas tiveram relacao direta com os sintomas visuais de toxicidade. Os porta-enxertos CAPI 4, CCP 09 e BRS 226 foram classificados como sensivel, intermediario e resistente a salinidade elevada, respectivamente. Essa variacao foi decorrente da influencia do porta-enxerto na particao do Na+ e do Cl-.

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.

Salt-induced changes in antioxidative enzyme activities in root tissues do not account for the differential salt tolerance of two cowpea cultivars

The salt stress effect in root growth and antioxidative response were investigated in two cowpea cultivars which differ in salt tolerance in terms of plant growth and leaf oxidative response. Four-day-old seedlings (establishment stage) were exposed to 100 mM NaCl for two days. The roots of the two cultivars presented distinct response in terms of salt-induced changes in elongation and dry weight. Root dry weight was only decreased in Perola (sensitive) cultivar while root elongation was mainly hampered in Pitiuba (tolerant). Root relative water content remained unchanged under salinity, but root Na+ content achieved toxic levels as revealed by the K+/Na+ ratio in both cultivars. Then, root growth inhibition might be due to ionic toxicity rather than by salt-induced water deficit. Although electrolyte leakage markedly increased mainly in the Perola genotype, lipid peroxidation decreased similarly in both salt-stressed cultivars. APX and SOD activities were reduced by salinity in both cultivars reaching similar values despite the decrease in Pitiuba had been higher compared to respective controls. CAT decreased significantly in Pitiuba but did not change in Perola, while POX increased in both cultivars. The salt-induced decrease in the CAT activity of Pitiuba root is, at principle, incompatible to allow a more effective oxidative protection. Our results support the idea that the activities of SOD, APX, CAT and POX and lipid peroxidation in cowpea seedling roots were not associated with differential salt tolerance as previously characterized in terms of growth rate and oxidative response in plant leaves.

Differences in Cowpea Root Growth Triggered by Salinity and Dehydration are Associated with Oxidative Modulation Involving Types I and III Peroxidases and Apoplastic Ascorbate

The aim of this work was to investigate the balance between the activities of ascorbate peroxidase (APX) and phenol peroxidases (POD) and cowpea root growth in response to dehydration and salt stress. Root growth and indicators of oxidative response were markedly changed in response to salinity and dehydration. Salt treatment strongly inhibited root elongation, which was associated with an increase in lignin content and a significant decrease in the concentrations of apoplastic hydrogen peroxide (H2O2) and ascorbate. In conditions of extreme salinity, cytosol–APX activity was significantly decreased. In contrast, cell-wall POD activity was greatly increased, whereas lipid peroxidation was unchanged. These results indicate that POD could be involved in both H2O2 scavenging and the inhibition of root elongation under high salinity. In contrast, dehydration stimulated primary root elongation and increased lipid peroxidation and apoplastic ascorbate content, but it did not change APX and POD activities or H2O2 concentration. When cowpea roots were subjected to salinity followed by dehydration, the water and pressure potentials were decreased, and lipid peroxidation was markedly increased, highlighting the additive nature of the inhibitory effects caused by salt and dehydration. The proline concentration was markedly increased by dehydration alone, as well as by salt followed by dehydration, suggesting a possible role for proline in osmotic adjustment. Salinity and dehydration induce contrasting responses in the growth and morphology of cowpea roots. These effects are associated with different types of oxidative modulation involving cytosolic-APX and cell-wall POD activities and apoplast H2O2 and ascorbate levels.

Atividade de enzimas antioxidantes e inibição do crescimento radicular de feijão caupi sob diferentes níveis de salinidade

Phenol peroxidase (POX) is a dual enzyme that is involved with hydrogen peroxide scavenging and lignin biosynthesis, contributing to growth inhibition by secondary wall thickening. In order to relate growth inhibition to salt-induced oxidative modulation, the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and POX were evaluated in cowpea roots under salinity. Four-day-old seedlings of the Pitiuba and Perola cultivars were exposed to 0, 25, 50, 75 and 100 mM NaCl in germination paper under controlled conditions. After two days of treatment, root length was reduced under 100 mM NaCl by 56 and 26% in Pitiuba and Perola, respectively, which was associated with enhanced electrolyte leakage and cell death in the root apex. NaCl salinity did not trigger lipid peroxidation, indicating that cell death was probably due to membrane damage instead of oxidative stress. Salt stress reduced the activity of SOD, CAT and APX and increased the POX activity, demonstrating that this enzyme plays a role in oxidative protection in cowpea roots exposed to NaCl salinity. In conclusion, salt-induced growth inhibition in cowpea roots could be attributed, at least in part, to a coordinate action involving an increase in POX activity and a drop in CAT and APX activities.