Differential Responses of Antioxidant Enzymes in Salt-Stressed Almond Tree Grown Under Sun and Shade Conditions

We studied the effects of solar irradiance on antioxidant enzymes and polyphenols in sweet almond cv. Mazzetto grown in salt soil. Photosynthetic performance, leaf pigments, activities of antioxidant enzymes and concentrations of polyphenols were measured in plants growing in shade or full sun and supplied with 100 mM NaCl over a 4-week period. In response to the salt stress treatment, photosynthetic rates decreased more in sun plants than in shade plants, likely because of declines in chlorophyll and carotenoids content coupled with significant reductions in stomatal conductance and MDA increases. Antioxidant enzymatic activities such as APX and POD were much greatest in sun leaves under unstressed conditions, however it increased in response to salt stress more in shade leaves. Whereas, Cat decreased under all treatments. Polyphenols markedly increased in response to full sunlight irrespective of salt treatment; however, polyphenols concentrations increased more in response to salt stress in shade leaves.