Expressão de caracteres fisiológicos induzida por estresse salino em três progênies de cajueiro

Abstract

The main aim of this study was to test the hypothesis that cashew seedlings from diverse environmental conditions show different biochemical and physiological characters in response to salt stress. Different cashew plant genotypes regionally known as "comum" (Anacardium occidentale L.) from coastal dunes subjected to salinization, "anão-precoce CP76" (Anacardium occidentale L var. nanum) and "microcarpo" (Anacardium microcarpum Ducke) — a native cashew plant species were evaluated in relation to their response to NaCI salinity during the initial growth. Plants were grown either in sand culture or on vermiculite, under different NaCI levels (0, 50, 100, 150 e 200 mM) and at different time exposure. Plants were cultured under greenhouse condition at a 12 h photoperiod, reaching the maximal photosinthetic active radiation of 1,000 µmol..m2.s1. Average temperatures were 27 °C at night and 24 °C by day, while average air humidity ranged between 40% and 80%. The results show that microcarpo cashew plants was the most sensitive of the three genotypes studied, concerning dry mass decrease and leaf visual toxicity sympthoms. Microcarpo sensitiviness to NaCI was directedly related to leaf C1 and Na+ content, to a higher Clleaf/root relation, and also to a lower leaf proline accumulation. In spite of the fact that "comum" and "anão" cashew stock plants show great phenotypical differences, the derived seedlings did not exhibit much contrast as to salt tolerance, although "anão" presented more root and shoot biomass on both control and salt treatment. Although the physiological characters studied (inorganic ion accumulation and partitioning, organic ion accumulation, enzyme activities of inorganic N assimilation, porometric measurements — stomatal behaviour and leaf transpiration rate) exhibit outstanding alterations in response to salt stress, they could not explain the the distinct NaCI sensibility presented by the three genotypes. Anyways, salt stress affected more decissively root endogenous K+ level, leaf expasion, nitrate reductase activity, stomatal conductance and Ca+2 and Mg+2 in leaf. On the other way, gluthamine sinthetase and soluble sugar content were less affected by salinity. Consequentely, only Na+ and Cl- accumulation as well as proline level colud partially explain NaCI sensibility. In general, cashew seedling responses to NaCI are extremely complex and suggest that the characters that may confer tolerance do not act isolatedely but are rather interactive.