Changes in protein content, protease activity, and amino acid content associated with heat injury in creeping bentgrass

Various physiological processes may deteriorate in response to increasing temperatures, contributing to the decline in turf quality for cool-season turfgrasses during heat stress. This study was performed to investigate metabolic changes (membrane lipid peroxidation, total protein content, amino acid content, and protease activity) associated with turf quality decline for creeping bentgrass (Agrostis stolonifera Huds.) in response to gradually increasing temperatures for a short duration and prolonged exposure to lethally high temperature. Plants were subjected to increasing temperatures of 20, 25, 30, 35, and 40 degrees C for 7 days at each level of temperature [gradual heat stress (GHS)] or exposed to high temperature of 40 degrees C for 28 days [prolonged heat stress (PHS)] in growth chambers. During the GHS treatment, significant decline in turf quality occurred when plants were exposed to 30 degrees C for 7 days; simultaneously, malondialdehyde (MDA) content increased and total protein content in shoots decreased significantly compared to those at 20 degrees C. Protease activity increased at 25 degrees C and then decreased as temperature was elevated from 30 to 40 degrees C during the GHS treatment. Amino acid content decreased under GHS, beginning at 25 degrees C. Under the PHS treatment, turf quality declined and MDA content increased significantly, beginning at 14 days of PHS, while total protein content decreased at 7 days of PHS. Protease activity and amino acid content increased at 7 days of PHS, and then declined with longer stress duration. Our results indicated that protease activity, and amino acid and total protein content were more responsive to GHS or PHS than that of lipid peroxidation and turf quality. Changes in metabolic parameters of protease activity, amino acid and total protein content, and lipid peroxidation may contribute to leaf senescence and poor turf performance under severe or prolonged heat stress conditions for creeping bentgrass.