Effects of foliar-applied ethylene inhibitor and synthetic cytokinin on creeping bentgrass to enhance heat tolerance
Heat stress is a major factor causing leaf senescence and other physiological damages in cool-season grass species. Cytokinins and ethylene are two major plant hormones affecting leaf senescence. The objective of this study was to determine whether foliar application of an ethylene synthesis inhibitor (aminoethoxyvinylglycine, AVG) and a synthetic cytokinin (trans-zeatin riboside, t-ZR) would enhance creeping bentgrass (Agrostis stolonifera L.) tolerance to heat stress associated with the suppression of leaf senescence. Creeping bentgrass ‘Penncross’ was exposed to either heat stress (35°C) or optimal growth temperature (20°C) for 35 d in growth chambers. Plants at each temperature were treated with 25 µM AVG, 25 µM t-ZR or water (control). Foliar spray of AVG or zeatin riboside (ZR) solution resulted in increases in turf quality, leaf chlorophyll content, activities of antioxidant enzymes, and the reduction in lipid peroxidation, compared with water-treated plants, for plants exposed to heat stress. In addition, foliar application of AVG suppressed ethylene evolution, whereas exogenous ZR resulted in elevated endogenous cytokinin levels under heat stress. The results suggest that the application of AVG or ZR suppressed leaf senescence and improved heat tolerance of creeping bentgrass, which could be because of their effects on endogenous production of ethylene and cytokinins and on antioxidant metabolism.