Drought induces oxidative stress in pea plants

Pea (Pisum sativum L. cv. Frilene) plants subjected to drought (leaf water potential of -1.3 MPa) showed major reductions in photosynthesis (78), transpiration (83), and glycolate oxidase (EC 1.1.3.1) activity (44), and minor reductions (18) in the contents of chlorophyll a, carotenoids, and soluble protein. Water stress also led to pronounced decreases (72–85) in the activities of catalase (EC 1.11.1.6), dehydroascorbate reductase (EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2), but resulted in the increase (32–42) of non-specific peroxidase (EC 1.11.1.7) and superoxide dismutase (EC 1.15.1.1). Ascorbate peroxidase (EC 1.11.1.11) and monodehydroascorbate reductase (EC 1.6.5.4) activities decreased only by 15 and the two enzymes acted in a cyclic manner to remove H₂O₂, which did not accumulate in stressed leaves. Drought had no effect on the levels of ascorbate and oxidized glutathione in leaves, but caused a 25 decrease in the content of reduced glutathione and a 67 increase in that of vitamin E. In leaves, average concentrations of catalytic Fe, i.e. Fe capable of catalyzing free-radical generation by redox cycling, were estimated as 0.7 to 7 M (well-watered plants, depending on age) and 16 M (water-stressed plants); those of catalytic Cu were 4.5 M and 18 M, respectively. Oxidation of lipids and proteins from leaves was enhanced two- to threefold under stress conditions and both processes were highly correlated. Fenton systems composed of the purported concentrations of ascorbate, H₂O₂, and catalytic metal ions in leaves produced hydroxyl radicals, peroxidized membrane lipids, and oxidized leaf proteins. It is proposed that augmented levels and decompartmentation of catalytic metals occurring during water stress are responsible for the oxidative damage observed in vivo.Abbreviations and Symbol ASC ascorbate - DW dry weight - DHA dehydroascorbate - GSH reduced glutathione - GSSG oxidized glutathione - MDHA monodehydroascorbate (ascorbate free radical) - SOD Superoxide dismutase - _wa water potential We thank Dr. R. Picorel (E.E. de Aula Dei, CSIC) for allowing us access to HPLC equipment. J.F.M., 1.1., and S.F. were the recipients of predoctoral fellowships from the Comunidades Autónomas de Aragon, Pais Vasco, and Navarra, respectively. R.V.K. thanks the U.S. Department of Agriculture (grant 91-37305-6705) for travel support. This work was financed by grants from the Comisión Interministerial de Ciencia y Tecnología (AGR-91-0857-C02 to P.A. and M.B.) and the Dirección General de Investigación Científica y Técnica (PB92-0058 to M.B) of Spain.