EFFECT OF FLOODING ON THE ACTIVITIES OF SOME ENZYMES OF ACTIVATED OXYGEN-METABOLISM, THE LEVELS OF ANTIOXIDANTS, AND LIPID-PEROXIDATION IN SENESCING TOBACCO-LEAVES

Effects of flooding on the activities of some enzymes of activated oxy gen metabolism, the levels of antioxidants, and lipid peroxidation in senescing leaves of tobacco were investigated. As judged by the decrea se in chlorophyll and protein levels, flooding accelerated the senesce nce of tobacco leaves. Total peroxide and the lipid peroxidation produ ct, malondialdehyde, increased in both control and flooding-treated le aves with increasing duration of the experiment. Throughout the durati on of the experiment, flooded leaves had higher levels of total peroxi de and malondialdehyde than did control leaves. Flooding resulted in a n increase in peroxidase and ascorbate peroxidase activities and a red uction of superoxide dismutase activity in the senescing leaves. Glyco late oxidase, catalase, and glutathione reductase activities were not affected by flooding. Flooding increased the levels of total ascorbate and dehydroascorbate. Total glutathione, reduced form glutathione, or oxidized glutathione levels in flooded leaves were lower than in cont rol leaves during the first two days of the experiment, but were highe r than in control leaves at the later stage of the experiment. Our wor k suggests that senescence of tobacco induced by flooding may be a con sequence of lipid peroxidation possibly controlled by superoxide dismu tase activity. Our results also suggest that increased rates of hydrog en peroxide in leaves of flooded plants could lead to increased capaci ties of the scavenging system of hydrogen peroxide.