Nitric oxide alleviates lipid peroxidation induced by osmotic stress during senescence of detached leaves of Malus hupehensis Rehd.

The protective effect of nitric oxide (NO) against membrane lipid peroxidation induced by polyethylene glycol (PEG) osmotic stress was investigated in relation to the metabolism of reactive oxygen species (ROS) and proline accumulation during the senescence of detached leaves of Malta hupehensis Rehd. in the dark. Membrane lipid peroxidation was determined by measuring the increase in malondialdehyde (MDA) content. PEG-induced osmotic stress resulted in a marked increase in the contents of MDA and proline, as well as the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Sodium nitroprusside (SNP), a donor of NO, prevented the PEG-induced increase in MDA content, but, with an increase in proline content as well as increases in the activities of CAT and APX, and in the levels of superoxide anions and hydrogen peroxide (H2O2). Treatment with SNP alone also alleviated lipid peroxidation, compared to water-treated leaves, with an increased proline content and SOD activity, but decreased the levels of superoxide anions and H2O2. We concluded that NO was effective at alleviating membrane lipid peroxidation induced by osmotic stress (PEG) during the senescence of detached leaves of M. hupehensis Rehd., suggesting a similar role for NO as in the regulation of ROS-dependent lipid peroxidation in animals. The relationships between NO-mediated regulation of lipid peroxidation and ROS metabolism, as well as proline accumulation, are discussed.