Effect of Paclobutrazol on the Activities of some Enzymes of Activated Oxygen Metabolism and Lipid Peroxidation in Senescing Soybean Leaves

Abstract

Summary Nineteen-day-old soybean [Glycine max (L.) Merr. cv. A 2] plants were treated with soil-applied paclobutrazol, an antigibberellin growth inhibitor, at the rate of 125 µg per 10 cm pot. The plants were then grown for 14 days under a 14 hr photoperiod after which they were transferred to the dark for senescence induction. At the end of the 14 day period in the light, treated plants exhibited higher chlorophyll (Chl) content and higher activities of catalase and glycolate oxidase compared to controls. In contrast, control leaves had higher activities of superoxide dismutase and a higher content of malondialdehyde (MDA), a product of lipid peroxidation. Upon transfer to dark, Chl and protein content declined in both control and treated plants, but the decline was much faster in controls. The activity of catalase declined markedly in controls while remaining constant in reated plants. Peroxidase and superoxide dismutase activities and MDA content increased in controls in the dark but remained relatively constant in treated plants. These results suggest that paclobutrazol delays dark-induced senescence in attached soybean leaves and that this delay is associated with the maintenance of catalase activity and the prevention of the senescence-linked rise in peroxidase activity and lipid peroxidation.