Cytokinin effects on creeping bentgrass response to heat stress: II. Leaf senescence and antioxidant metabolism

In another study, results of growth responses to cytokinin indicate that heat stress injury in creeping bentgrass can be alleviated to some extent by injection of cytokinin to the root zone. The objective of this study was to examine whether the alleviating effects of exogenous application of a cytokinin on heat injury in creeping bentgrass (Agrostis palustris L.) involve regulation of antioxidant activities. Creeping bentgrass was exposed to three air/soil temperature regimes for 56 d in growth chambers: (i) low air and soil temperature control (20/20°C); (ii) high soil temperature (20/35°C); and (iii) high air/soil temperatures (35/35°C). Four different concentrations (0.01, 0.1, 1, and 10 μmol) of zeatin riboside (ZR) or water (control) were injected into the root zone (0 to 5 cm depth) of plants on the day before heat stress was imposed (0 d) and 14 d after. Leaf electrolyte leakage (EL) and the content of a lipid peroxidation product, malondialdehyde (MDA), increased, whereas leaf chlorophyll content and activities of superoxide dismutase (SOD) and catalase (CAT) decreased at 20/35°C or 35/35°C for ZR-untreated plants. Exogenous ZR significantly suppressed these responses under both high temperature regimes. Application of 10 μmol ZR was most effective in slowing leaf senescence and alleviating heat-induced lipid peroxidation of cell membranes, followed by 1 μmol at 35/35°C. Applying 0.1 and 0.01 μmol ZR had no effects on creeping bentgrass responses to 20/35 or 35/35°C. Our results suggested the alleviating effects of ZR at 1 and 10 μmol in heat injury to creeping bentgrass was related to the inhibition of lipid peroxidation and slowing leaf senescence.