ANTIOXIDANT RESPONSE TO NACL STRESS IN SALT-TOLERANT AND SALT-SENSITIVE CULTIVARS OF COTTON

The mechanism(s) imparting salt tolerance to plants remains unresolved. Although cotton (Gossypium hirsutum L.) is classified as a salt-tolerant plant, variation in salt tolerance has been observed among different cultivars. The purpose of this study was to determine if more salt-tolerant cultivars contain higher constitutive or inducible levels of antioxidants than more salt-sensitive cultivars. Greenhouse-grown salt-tolerant (cv. Acala 1517-88 and Acala 1517-SR2) and salt-sensitive (cv. Deltapine 50 and Stoneville 825) cotton plants treated with either 0 or 150 mM NaCl were analyzed for differences in growth and antioxidant capacities. The 150 mM NaCl treatment resulted in more than 40% reduction in growth of Deltapine 50 and Stoneville 825 and less than 30% reduction in the Acala cultivars. The more salt-tolerant cultivars had higher constitutive levels of catalase (121-215%) and alpha-tocopherol (312-420%). The salt treatment resulted in a 38 to 72% increase in peroxidase activity and a 55 to 101% increase in glutathione reductase activity in the Acala cultivars while the activities of these enzymes remained constant or decreased in the more sensitive cultivars. The Acala cultivars also exhibited a lower oxidized/reduced ascorbic acid ratio and a higher reduced/oxidized glutathione ratio than the more sensitive cultivars when grown at 150 mM NaCl. When subjected to a one-time salt treatment, lipid peroxidation in Deltapine 50 increased 51% over Acala 1517-88. These data indicate that protection from oxidative damage by higher levels of antioxidants and a more active ascorbate-glutathione cycle may be involved in tbe development of salt tolerance in cotton.