Caution, Students at Large

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

Root electrolyte leakage (A) and MDA content (B) of <i>A</i>. <i>stolonifera</i> and <i>A</i>. <i>scabra</i> following control and heat stress treatment.

<p>Data shown are the mean ± SE of four biological replicates. Different letters atop bars indicate significant differences exist at the P ≤ 0.05 level.</p

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

<p>Relative quantities of organic 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

Transcript level of <i>SOD</i> (A), <i>POD</i> (B) and <i>CAT</i> (C) in roots of control or heat-stressed <i>A</i>. <i>stolonifera</i> and <i>A</i>. <i>scabra</i>.

<p>Data shown are the mean ± SE of four biological replicates. Different letters atop bars indicate significant differences exist at the P ≤ 0.05 level.</p

Reduced ascorbate (A), total ascorbate (B) and glutathione (C) content in <i>A</i>. <i>stolonifera</i> and <i>A</i>. <i>scabra</i> roots under control and heat stress condition.

<p>Data shown are the mean ± SE of four biological replicates. Different letters atop bars indicate significant differences exist at the P ≤ 0.05 level.</p

Effects of elevated CO₂ on turf quality responses to increasing temperatures at 7 d (a), 14 d (b), 21 d (c), and 28 d (d) of temperature treatment.

<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 0.1198 and 0.0284 under ambient and elevated CO₂ concentration, respectively, at 7 d, 0.0283 and 0.0229 at 14 d, 0.1909 and 0.1685 at 21 d, and 0.1928 and 0.1732 at 28 d.</p

Histochemical staining of <i>A</i>. <i>stolonifera</i> (A to F) and <i>A</i>. <i>scabra</i> (G to L) root tips under control and heat stress conditions using DAB.

<p>Bar represents 100 μm.</p

Effects of elevated CO₂ on the responses of shoot dry weight (a), root dry weight (b), and root/shoot dry weight ratio (c) to increasing temperatures at 28 d of temperature treatment.

<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 0.7078 and 0.9462 under ambient and elevated CO₂ concentration, respectively.</p

Root respiration rate for <i>A</i>. <i>stolonifera</i> and <i>A</i>. <i>scabra</i> under heat stress condition as affected by SNP or SHAM.

<p>Data shown are the mean ± SE of four biological replicates. Different letters atop bars indicate significant differences exist at the P ≤ 0.05 level.</p