Effects Of Exogenous Nitric Oxide On Hydrogen Peroxide Metabolism And Aging Process Of Wheat(Triticum Aestivum L.) Leaves

As a nontraditional regulator of plant growth, nitric oxide (NO) participated in many physiological responses of plant, such as germination, growth, programmed cell death (PCD), defense responses and ethylene emission. However, whether and how NO played a role during plant aging process were still unclear. The present work focused on the effects of exogenous nitric oxide on hydrogen peroxide (H202) metabolism hi wheat (Triticum aestivum L.) leaves, and further investigated the regulational roles and mechanism of NO on the aging process of wheat leaves.Treatment with different concentrations of sodium nitroprusside (1 mmol/L and 5 mmol/L SNP), a nitric oxide donor in vitro, enhanced H2O2 levels significantly within the first 30 minutes of incubation with detached wheat leaves. Meanwhile, guaiacol peroxidase (POD) activities were dramatically inhibited, and the activities of catalase (CAT) decreased slightly. However, prolonging the treatment to 240 minutes gradually reduced the content of H2O2, which might be due to the restoration of CAT activities rather than consistent inhibition of POD. In vitro experiments also indicated that the inhibition of wheat POD in crude extracts by varying concentrations of SNP might appear to be irreversible in comparison with the reversible inhibition of CAT. Therefore, NO played a role in regulating H2O2 levels in detached wheat leaves in vivo by different inhibiting modes of POD and CAT.When wheat leaves (2nd leaves) were treated with different concentrations (0,0.05,0.1,0.2, 0.5 mmol/L) of nitric oxide donor, sodium nitroprusside (SNP), the contents of H2O2 and malondialdehyde (MDA) reduced at the low concentration (0.05, 0.1, 0.2 mmol/L) treatments, while the above contents enhanced at the high concentration of SNP (0.5 mmol/L). Among the low concentration treatments, the protective effect of 0.1 mmol/L SNP was the most obvious. Furthermore, the treatment with 0.1 mmol/L SNP on the leaves of different positions attenuated the accumulation of H2O2, superoxide anion radical (O2 ~) and MDA levels, alsocounteracted the degradation of chlorophyll and soluble proteins, especially Rubisco, both of which led to the effective delay of aging process in wheat leaves. In vitro aging experiments in chloroplasts, the effects of different SNP concentrations (0, 0.05, 0.1, 0.2, 0.5, 1, 5 mmol/L) also displayed dual roles, one of which, 0.2 mmol/L SNP treatment, protected the membrane structure and attenuated the degradation of Rubisco effectively. Above results indicated that low concentrations of NO played a role in delaying aging process in wheat leaves, which might contribute to the decrease of ROS levels and the alleviation of the further oxidative damage caused by ROS.