[Hydrogen peroxide is involved in regulation of tobacco leaf senescence]

Effects of various exogenous hydrogen peroxide (H2O2) concentrations on leaf senescence of tobacco (Nicotiana tabacum L.) were studied. The results showed that 0.1 and 1 mmol/L H2O2 had little effects on the leaf senescence of tobacco, the contents of chlorophyll and soluble protein were decreased in varying degrees by 10, 100 mmol/L H2O2 treatment, the decreased chlorophyll and soluble protein contents were significantly correlated with increased endogenous H2O2 content. SDS-PAGE of soluble protein and localized staining of H2O2 showed consistency with respective content. Chloroplast ultrastructure were observed in the mesophyll cells of tobacco and there was a little change by 10 mmol/L H2O2 treatment, and a remarkable breakdown of granal stacks and disorganized thylakoid membranes were revealed by 100, 200 mmol/L H2O2 treatment. RT-PCR analysis showed the expression level of senescence associated genes SAG12 was low by 10mmol/L H2O2 treatment and increased by 100 mmol/L H2O2 treatment. These results strongly suggested the tobacco leaf senescence was induced by 10 mmol/L H2O2 and accelerated the progression by high concentration (100, 200 mmol/L) H2O2 stress.