Abstract
The exogenous application of ethylene inhibitors, cyotkinins, or nitrogen has previously been shown to suppress heat-induced senescence and improve heat tolerance in cool -season grasses. The objectives of this study were to examine metabolic profiles altered by exogenous treatment of creeping bentgrass with an ethylene inhibitor, cytokinin or nitrogen under heat stress and to determine metabolic pathways regulated by those compounds in association with their effectiveness for improving heat tolerance. Creeping bentgrass (Agostis stolonifera) plants (cv. Penncross) were foliar sprayed with 18 mM carbonyldiamide (N source), 25μM aminoethoxyvinylglycine (AVG, ethylene inhibitor), 25μM zeatin riboside (ZR, cytokinin), or a water control, and then exposed to 20/15°C (day/night) or 35/30°C (heat stress) in growth chambers. All three exogenous treatments suppressed leaf senescence, as manifested by increased turf quality and chlorophyll content, and reduced electrolyte leakage under heat stress. Polar metabolite profiling identified increases in the content of certain organic acids (i.e. citric and malic acid), sugar alcohols, disaccharides (sucrose), and decreased accumulations of monosaccharides (i.e. glucose and fructose) with exogenous treatment of N, AVG, or ZR at the previously mentioned concentrations when compared to the untreated control under heat stress. Nitrogen stimulated amino acid accumulation whereas AVG and ZR reduced amino acid accumulation compared to the untreated control under heat stress. These results revealed that the alleviation of heat-induced leaf senescence by N, AVG, and ZR could be due to changes in the accumulation of metabolites involved in osmoregulation, antioxidant metabolism, carbon and nitrogen metabolism, as well as stress signaling molecules.
Highlights
Heat is a major abiotic stress which leads to premature leaf senescence in many plant species, including cool-season grass species
Plants treated with N, ZR, or Aminoethoxy vinyl glycine (AVG) had significantly lower Electrolyte leakage (EL) at 21 and 28 d of heat stress compared to the untreated control
The greater accumulation of sugar alcohols in plants treated with AVG, ZR, or N compared to the untreated control under heat stress suggested that those sugar alcohols could be involved in the suppression of heat-induced leaf senescence by AVG, ZR, or N
Summary
Heat is a major abiotic stress which leads to premature leaf senescence in many plant species, including cool-season grass species. Many approaches have been used to alleviate heat stress-induced senescence and improve whole-plant stress tolerance, including exogenous application of plant growth regulators or hormones, such as ethylene inhibitors and cytokinins and nutrients, such as nitrogen [2,3,4]. Decreased levels of ethylene production have been associated with improved stress tolerance in a cool-season grass species [10]. The use of AVG to reduce endogenous ethylene levels delay senescence has been demonstrated in a number of species including oat (Avena sativa), wheat (Triticum aestivum), and creeping bentgrass [2, 12, 13]. Specific metabolites regulated by an ethylene inhibitor that may suppress heat-induced leaf senescence are yet to be determined
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