Nitric oxide improves chilling tolerance of maize by affecting apoplastic antioxidative enzymes in leaves

The effects of nitric oxide (NO) on chilling tolerance (freezing injury, ice nucleation activity, contents of hydrogen peroxide and superoxide anion, and lipid peroxidation level) and the activities of apoplastic antioxidant enzymes (peroxidase and superoxide dismutase) were investigated in the leaves of maize (Zea mays) exposed to short-term chilling. NO treatment was carried out through spraying of sodium nitroprusside (SNP), which is a donor of NO, in concentrations of 0.0, 0.1 and 1 mu M on the leaves of 10-day plants. The plants then were transferred into the chilling condition (10/7 A degrees C) 2 days before the harvesting of leaves (14th and 21th days). Application of 0.1 mu M NO had more effect on the alleviation by decreasing the freezing injury in maize at least for 11 days after the application. Both concentrations of NO generally increased ice nucleation activity of apoplastic proteins extracted from leaves. The SNP applications decreased the contents of reactive oxygen species such as hydrogen peroxide and superoxide anion and the level of lipid peroxidation, while further increasing the activities of the apoplastic antioxidant enzymes studied. The results show that exogenous NO treatment provides important contributions to increasing the chilling tolerance of maize by regulating the biochemical mechanisms of chilling response, including apoplastic antioxidant enzymes. It can be seen that the NO treatment can play positive roles in alleviating chilling-induced damage in maize. Therefore, it is suggested that NO treatments may contribute to research studies related to diminishing chilling-induced damage in agricultural applications.