Suppression of heat-induced leaf senescence by γ-aminobutyric acid, proline, and ammonium nitrate through regulation of chlorophyll degradation in creeping bentgrass

Heat-induced leaf senescence may be regulated by nitrogen or nitrogen-enriched amino acids. The objectives of the current study were to examine whether exogenous application of.-aminobutyric acid (GABA), proline, and ammonium nitrate (N) could alleviate heat-induced leaf senescence in creeping bentgrass (Agrostis stolonifera L.) and to determine whether the effects of GABA, proline, and N on heat-induced leaf senescence were associated with the alteration of chlorophyll (Chl) metabolism. Plants were exposed to heat stress (35/30 degrees C, day/night) or non-stress (22/18 degrees C, day/night) temperature conditions for 35 d in controlled-environment growth chambers. Turf quality, Chl content, and photochemical efficiency declined whereas the activities of Chl-degrading enzymes (chlorophyllase and pheophytinase) increased in response to heat stress. Application of GABA, proline, or N significantly enhanced turf quality, Chl content, and photochemical efficiency, and suppressed Chl-degrading enzyme activities under heat stress. The activity of a Chl-synthesizing enzyme (porphobilinogen deaminase) was not affected by GABA, proline, or N application. These results indicate that heat-induced leaf senescence could be mainly due to heat-accelerated Chl degradation, and GABA, proline, or N could suppress Chl degradation, alleviating heat-induced leaf senescence in creeping bentgrass.