Reduction of paraquat-induced oxidative stress in Phaseolus vulgaris and Malus domestica leaves by α-tocopherol

Studies of the biological efficiency of the antioxidant alpha -tocopherol against oxidative stress were performed under controlled conditions on primary leaves of Phaseolus vulgaris grown in a plant growth chamber and on leaves of Malus domestica trees grown in containers under field conditions. Application of 40 mul of an aqueous alpha -T'OH solution (0.25% a.i.) to the upper leaf surface was followed by application of 20 mul of an aqueous solution of the herbicide paraquat (1,1'-dimethyl-4,4'-bipyridinium-dichloride) to the lower surface of P. vulgaris leaves 4, 24, 48 and 96 h after the tocopherol application. Paraquat is typically used for the induction of oxidative stress. Paraquat solution was also applied to M. domestica leaves 24 h after alpha -T'OH application. The chlorophyll fluorescence (CF) and chlorophyll content of plant tissue were measured 24 h following the paraquat treatment in M. domestica leaves. Subsequently the endogenous tocopherol content was determined in the treated leaf areas. The numbers and area of necrotic lesions were evaluated 24 h after paraquat was applied. Applications of alpha -tocopherol resulted in a lower sensitivity of P. vulgaris and M. domestica leaves to paraquat-induced stress, as compared to the control treated with paraquat only. This was documented by measurement of specific CF parameters, giving precise information on the degree of impairment of the stress-sensitive electron transport in the chloroplasts. Endogenous alpha -tocopherol and chlorophyll content were less affected by paraquat in leaves pretreated with alpha -tocopherol. Hence, alpha -tocopherol treatment prior to paraquat application significantly reduced the number of paraquat-induced necrotic lesions on P. vulgaris leaves by 88% and the area of leaf damage by 55% in M. domestica. (C) 2001 Elsevier Science B.V. All rights reserved.