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Jatropha curcas L. is a multipurpose species of the Euphorbiaceae family that is widespread in arid and semiarid regions. This study investigated the ultrastructural and biochemical changes induced by salt stress during J. curcas seed germination and seedling development. Salt stress negatively affected seed germination and increased Na+ and Cl– contents in endosperms and embryo-axis. Lipids represented the most abundant reserves (64% of the quiescent seed dry mass), and their levels were strongly decreased at 8 days after imbibition (DAI) under salinity stress. Proteins were the second most important reserve (21.3%), and their levels were also reduced under salt stress conditions. Starch showed a transient increase at 5 DAI under control conditions, which was correlated with intense lipid mobilisation during this period. Non-reducing sugars and free amino acids were increased in control seeds compared with quiescent seeds, whereas under the salt-stress conditions, minimal changes were observed. In addition, cytochemical and ultrastructural analyses confirmed greater alterations in the cellular reserves of seeds that had been germinated under NaCl stress conditions. Salt stress promoted delays in protein and lipid mobilisation and induced ultrastructural changes in salt-stressed endosperm cells, consistent with delayed protein and oil body degradation.

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Sorghum (Sorghum bicolor) is an important species for semiarid regions, such as Brazilian Northeast, where soil salinization and water quality is becoming a striking problem.Several research centers have evaluated the role of different compounds capable to induce changes in plant metabolism and improve salt tolerance. For some abiotic stress, selenium (Se) emerges as an alternative to activate plant defense responses; however, its involvement in tolerance to salt stress remain poorly understood. Thus, this work aimed to evaluate the effects of exogenous selenium application on the growth of sorghum plants under salt stress. Sorghum plants from CSF 20 (salt-tolerant) and CSF 18 (salt-sensitive) genotypes were grown in nutrient solutions containing sodium selenite (Na2SeO3) at 0 (control), 2, 4, 8 and 16 μM, and subjected to 75 mM NaCl-stress. The analyses were done after ten days of saline treatments. Overall, the benefits effects of Se were observed only in sorghum plants from salt-sensitive genotype, whereas no expressive modulation was registered in the salt tolerant one. Although leaf area and root dry mass were severely decreased by salt stress, the salt negative effects were almost completely abolished by 16 μM-Se supply in salt-sensitive genotype; nonetheless, the same responses were not observed for dry mass of leaves. In conclusion, selenium supply may constitute a strategy to overcome salt damage in S. bicolor growth depending on dose and plant genotype. Diversos centros de pesquisa têm avaliado o papel de diferentes compostos na indução de alterações no metabolismo das plantas e na melhora da tolerância ao estresse salino. Para alguns estresses abióticos, o selênio (Se) surge como uma alternativa que induz respostas de defesa de plantas, no entanto seu envolvimento na tolerância de plantas ao estresse salino permanece pobremente compreendido. Assim, este trabalho teve como objetivo avaliar os efeitos da aplicação exógena de Se no crescimento de plantas de sorgo sob estresse salino. Plantas de sorgo dos genótipos CSF 20 (tolerante a sal) e CSF 18 (sensível a sal) foram cultivadas em soluções nutritivas contendo selenito de sódio (Na2SeO3) a 0 (controle), 2, 4, 8 e 16 μM e submetidas a estresse salino com NaCl a 75 mM. As análises foram feitas após dez dias dos tratamentos salinos. Em geral, os efeitos benéficos do Se foram observados apenas em plantas de sorgo do genótipo sensível ao sal, enquanto que nenhuma modulação expressiva foi registrada no tolerante. Embora a área foliar e a massa seca da raiz tenham sido severamente diminuídas pelo estresse salino, os efeitos negativos do sal foram quase completamente eliminados pelo fornecimento de Se a 16 μM no genótipo sensível. Contudo, as mesmas respostas não foram observadas para massa seca de folhas. Desta forma, o fornecimento de selênio pode constituir uma estratégia para superar os danos causados pelo estresse salino no crescimento de S. bicolor, porém seus efeitos são dependentes da dose e do genótipo da planta. KEYWORDS:

SUMMARY: Jatropha curcas L. is an oilseed plant that has been considered an alternative crop for semiarid regions, due to its adaptability to water deficit. This study aimed to evaluate the salt stress effects on germination and the antioxidative system of J. curcas seeds and seedlings. The germination parameters were significantly affected by salt treatment, and the percentage of seed germination was the most affected. The activities of antioxidative enzymes [superóxido dismutase, catalase (CAT), peroxidases do ascorbato e guaiacol] were significantly increased in salt-stressed endosperms and embryo axes at 6 and 8 DAS. Among these enzymes, CAT showed to be the strongest involved in hydrogen peroxide scavenging, due to CAT highest values in all evaluated periods, especially in salt stress conditions after germination. The lipid peroxidation was significantly highest until 4 DAS in control conditions; thereafter, these values sharply decreased. In addition, it was noticed that the antioxidative enzymes were not completely effective in avoiding the oxidative damages promoted by salt stress, which can have contributed to the high levels of lipid peroxidation, mainly at 6 and 8 DAS. We assumed that the increase in J.curcas antioxidant enzymatic system in the salt stress response may represent an adaptive condition to seed germination in saline conditions. KEYWORDS: Antioxidative enzymes, Lipid peroxidation, NaCl stress. AVALIAÇÃO DO ESTRESSE OXIDATIVO EM SEMENTES DE PALAVRAS-CHAVE:Enzimas antioxidativas, peroxidação lipídica, estresse salino.