Metabolite Responses to Exogenous Application of Nitrogen, Cytokinin, and Ethylene Inhibitors in Relation to Heat-Induced Senescence in Creeping Bentgrass.

Heat is a major abiotic stress which leads to the premature senescence of the widely used perennial grass species creeping bentgrass (Agrostis stolonifera). This premature senescence is associated with a host of physiological changes including altered energy relations induced by decreased photosynthesis and elevated respiration, changes to protein metabolism and increased protein degradation, as well as the production of damaging reactive oxygen species. The application of exogenous treatments such as plant hormones and plant growth regulators have previous been shown to result in improved stress tolerances. However the exact mechanisms by which these exogenous treatments delay heat induced senescence is not fully understood.  Creeping bentgrass plants (cultivar ‘Penncross’) were grown in environmental controlled growth chambers set to 20/15 ºC (day/night).  Plants were treated with exogenous applications of either nitrogen in the form of urea (N) at a 18mM concentration, cytokinin as zeatin riboside (ZR) at a 25 µM concentration, the ethylene inhibitor aminoethoxyvinylglycine (AVG) at a 25 µM concentration, or a water control 3 days prior to the in the induction of heat stress, and received subsequent applications at a 7 day interval.  Temperature treatments consisted of either heat stress conditions of 35/30 ºC or optimal conditions were plants remained at 20/15 ºC for 28 days.  Plants were assessed for heat tolerance using common physiological parameters including chlorophyll content, electrolyte leakage and a visual plant quality rating. Additionally tissue sample were taken for metabolite analysis. Plants treated with N, ZR, or AVG had delayed heat-induced senescence compared to the control treatment. Exogenous treatments resulted in significantly different levels of metabolites in several categories including organic acids such as citric acid, sugars including glucose and sucrose, and amino acids like proline.  The changes of these metabolites provide useful insight into the mechanisms by which these exogenous treatments may improve abiotic stress tolerance.