Effects of some oxidants and antioxidants on senescence of isolated leaves of sunflower with special reference to glycolate content, glycolate oxidase, and catalase activities

Abstract

Incubation of leaf discs of sunflower (Helianthus annuus L. cv. EC.68414) for 6 days in the dark caused a general decline in the contents of chlorophyll, protein, and glycolate in these tissues as well as in the activities of catalase and glycolate oxidase. Treatments with either glycolate or hydrogen peroxide decreased the contents of chlorophyll and protein and the activity of catalase but increased glycolate oxidase activity, hastening senescence. Treatments with ascorbate or 2-mercaptoethanol significantly arrested the decline in chlorophyll and protein levels, deferring senescence. Glycolate content was reduced in leaves treated with glycolate, hydrogen peroxide, ascorbate, or 2-mercaptoethanol. But the extent of reduction in the latter case was less pronounced than that following treatments with glycolate or hydrogen peroxide. Only the highest concentrations of either ascorbate or 2-mercaptoethanol increased the activity of catalase, whereas glycolate oxidase activity was increased by these chemicals in all concentrations.