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A black bundle of fur hurtled through the doorway of Elm Hall and darted down the hallway. Wild-eyed, a coed shrieked her way after the little animal. Screams echoed through the dormitory as other occupants discovered the object of the chase- a tiny skunk

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

<div><p>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 (<i>Agostis stolonifera</i>) 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.</p></div

Effects of elevated CO₂ on leaf photosynthetic rate (Pn) to leaf respiration rate (R) ratio (Pn/R) at different temperatures at 7 d (a), 14 d (b), 21 d (c), and 28 d (d) of temperature treatment, and the dotted line represents Pn/R ratio was 1.0.

<p>Vertical bars represent the values of least significant difference at p = 0.05 for comparison of CO₂ treatment effects at a given temperature.</p

Amino acid levels during heat stress for AVG, ZR, and N-treated plants, and the water-treated control.

<p>Relative quantities of amino acids at 28-d heat stress for AVG, ZR, and N-treated plants, and the water-treated control. Error bars indicate standard deviations and letters are statistical groups according to Fisher’s protected LSD (p = 0.05), with groups not containing the same letter being significantly different. Only metabolites which had at least one group significantly different from the others are presented.</p

Sugar alcohol levels during heat stress for AVG, ZR, and N-treated plants, and the water-treated control.

<p>Relative quantities of sugar alcohols at 28-d heat stress for AVG, ZR, and N-treated plants, and the water-treated control. Error bars indicate standard deviations and letters are statistical groups according to Fisher’s protected LSD (p = 0.05), with groups not containing the same letter being significantly different. Only metabolites which had at least one group significantly different from the others are presented.</p

Effects of elevated CO₂ on the relative organic acids content in leaves at 28 d of different temperature treatments.

<p>Vertical bars represent the values of least significant difference at p = 0.05 for comparison of CO₂ treatment effects at a given temperature. The LSD value for comparisons between temperature treatments was 0.0318 and 0.0171 under ambient and elevated CO₂ concentration, respectively.</p

Effects of elevated CO₂ on the relative soluble sugars content in leaves at 28 d of different temperature treatments.

<p>Vertical bars represent the values of least significant difference at p = 0.05 for comparison of CO₂ treatment effects at a given temperature. The LSD value for comparisons between temperature treatments was 0.0183 and 0.0223 under ambient and elevated CO₂ concentration, respectively.</p

Monosaccharide levels during heat stress for AVG, ZR, and N-treated plants, and the water-treated control.

<p>Relative quantities of monosaccharides at 28-d heat stress for AVG, ZR, and N-treated plants, and the water-treated control. Error bars indicate standard deviations and letters are statistical groups according to Fisher’s protected LSD (p = 0.05), with groups not containing the same letter being significantly different. Only metabolites which had at least one group significantly different from the others are presented.</p

Physiological effects of AVG, CK, and N in creeping bentgrass.

<p>Changes to turf quality (A), chlorophyll content (B), and electrolyte leakage (C) during 28 d of 20/15 C or 35/30 C when treated with AVG, ZR, N or water as a control. Vertical bars represent least significance difference values between exogenous treatments at p = 0.05.</p

Variable importance plot of metabolites during heat stress.

<p>Variable importance projection plot generated from the partial least squares regression highlighting which metabolites may potentially play a larger role in heat tolerance as predicted by the model. Wold’s citerion is denoted by a horizontal line.</p