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 the antioxidant response system in leaves from wheat (Triticum aestivum cv. Buck Poncho) subjected sequentially to drought and watering. Drought was imposed 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 approximately 2-fold increase in DCFDA oxidation rate. However, no significant effect either on lipid radical content or on hydroperoxide content was measured after drought and drought followed by watering. Microsomes isolated from leaves exposed to drought, and from leaves exposed to drought followed by watering, generated a significantly higher amount of hydroxyl radical as compared to microsomes isolated from control leaves, suggesting a higher production of hydroxyl radical in the cellular water-soluble phase, after drought and watering as compared to control values. The content of alpha-tocopherol in wheat leaves was increased 2.4-fold after drought and beta-carotene content was increased by 2.6-fold after drought. Hydration lowered lipid-soluble antioxidant content to control values. Total thiol content was increased by 70% after drought, and watering did not significantly alter the enhanced 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 reaction with an increased content of alpha-tocopherol and beta-carotene. Moreover, a co-ordinated response involving glutathione reductase activity, thiols and ascorbic acid is triggered to limit free radical dependent effects.