Drought and watering-dependent oxidative stress: effect on antioxidant content in Triticum aestivum L. leaves

The purpose of the present work was to evaluate both oxidative stress and t he antioxidant response system in leaves from wheat (Triticum aestivum cv. Buck Poncho) subjected sequentially to drought and watering. Drought was im posed by withholding water until soil water potential reached -2.0 MPa and maintained under those conditions for 24 h. DCFDA oxidation by wheat leaves was not significantly affected by drought, but watering led to an approxim ately 2-fold increase in DCFDA oxidation rate. However, no significant effe ct either on lipid radical content or on hydroperoxide content was measured after drought and drought followed by watering, Microsomes isolated from l eaves exposed to drought, and from leaves exposed to drought followed by wa tering, generated a significantly higher amount of hydroxyl radical as comp ared to microsomes isolated from control leaves, suggesting a higher produc tion of hydroxyl radical in the cellular water-soluble phase, after drought and watering as compared to control values. The content of alpha-tocophero l in wheat leaves was increased 2.4-fold after drought and beta-carotene co ntent was increased by 2.6-fold after drought. Hydration lowered lipid-solu ble antioxidant content to control values. Total thiol content was increase d by 70% after drought, and watering did not significantly alter the enhanc ed values. Drought decreased by 28.5% the content of reduced ascorbic acid. Taken as a whole, active species formed at wheat membranes after exposure to moderate water stress, are efficiently removed upon rehydration by react ion with an increased content of alpha-tocopherol and beta-carotene. Moreov er, a co-ordinated response involving glutathione reductase activity, thiol s and ascorbic acid is triggered to limit free radical dependent effects.