engleski

THE CORRELATION BETWEEN OXIDATIVE STRESS AND SENESCENCE IN TOBACCO (Nicotiana tabacum L.) LEAVES

The process of senescence is characterized by decline in photosynthesis and induction of oxidative stress. We investigated the process of natural senescence in tobacco leaves old 14, 30, 120 and 270 days and the process of premature senescence induced by hydrogen peroxide in 14d old leaves. Both natural and H2O2-induced senescence was accompanied by a decrease of chlorophylls content and by an increase of oxygen consumption. Effective quantum yield of PSII, F/F'm, declined in naturally senescent leaves and was not affected by exogenous H2O2. Both natural and H2O2-promoted senescence caused oxidative damage to lipids and proteins while DNA damage was noticed only in the oldest leaves (270 d). The process of natural senescence induced superoxide dismutase activity (H2O2-producing enzyme) and inhibited catalase and peroxidase activities (H2O2-destroying enzymes) Accordingly, endogenous H2O2 levels increased nearly linearly with progression of natural senescence. However, the promotion of senescence by the exogenous H2O2 was not associated with an increase in its endogenous level which is probably the result of increased ascorbate and pyrogallol peroxidase activities. Presented results show that increased radical levels displayed during natural senescence are not only caused by the elevated production of radicals but also by a loss in antioxidant capacity. The results also show the importance of hydrogen peroxide as a signal molecule.

tobacco; senescence; oxidative stress

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