Physiological and biochemical changes occurring in dwarf-cashew seedlings subjected to salt stress

Abstract

The effects of salt stress on some physiological and biochemical traits were evaluated in dwarf-cashew seedlings at the same developmental stage. Seeds were sown in trays containing vermiculite moistened with distilled water or with NaCl solutions having different electrical conductivities: 0.7, 1.8, 6.0, 9.8, 13.4, 17.4 and 20.6 dS m-1. Salinity delayed and inhibited seedling growth and development, particularly in the shoot. Concentrations of Na+ and Cl-, but not of K+, increased with increasing stress severity. With the exception of proline, concentration of organic solutes was only marginally affected by salt stress. Catalase activity in leaves increased slightly as a result of salt stress, whereas guaiacol peroxidase activity was induced only under low levels of salt. In contrast, activities of guaiacol peroxidase and ascorbate peroxidase increased dramatically in roots. Apparently, roots were better protected against oxidative damage than shoots, as judged from the decrease in lipid peroxidation in root tissues. In leaves, expression of 75 proteins, evaluated by 2D electrophoresis, was altered by salt stress: 35 of them increased their expression and three were apparently de novo synthesized. In roots, 69 proteins were modified by salt stress: 34 proteins increased their expression and two proteins appeared only in stressed seedlings. The changes in protein patterns were caused by the imposed salt stress rather than by a response to the developmental stage. Overall, these responses could play an important role in salt stress acclimation of cashew seedlings.