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The objective of this study was to investigate transcriptomic changes and molecular factors regulated by cytokinins that may contribute to improved drought tolerance in creeping bentgrass (Agrostis stolonifera) overexpressing adenine isopentenyltransferase (ipt). Wild-type (WT) and ipt-transgenic plants were maintained well irrigated or exposed to 21 days of drought stress in growth chambers. Transcriptomic analysis conducted by RNA-seq revealed 661 and 648 upregulated and 764 and 862 downregulated drought-responsive genes (DRGs) in the WT and ipt-transgenic plants, respectively, under drought stress using adjusted P-value of 0.001 and log2 fold change. Gene ontology (GO) term classification showed that a greater number of DRGs were found in ipt-transgenic plants than in WT plants pertaining to biological functions including metabolic process, cellular process, cell structure and growth, macromolecular complex, and binding and catalytic activity, whereas fewer DRGs were found in ipt-transgenic plants than in WT plants pertaining to response to stimulus and antioxidant activity. Furthermore, plant hormone signal transduction pathway analysis revealed three downregulated transcripts [type B - Arabidopsis response regulators (B- ARR), ABA-responsive element binding factor (ABF) and pyrabactin resistance/like (PYR/ PYL)] and two upregulated transcripts (BIN2 and JAZ) that were significantly differentiated between ipt-transgenic and WT plants under drought stress, which are particularly interesting for further investigation of molecular mechanisms of hormone-regulation of drought tolerance. [ABSTRACT FROM AUTHOR]

Abscisic acid (ABA), salicylic acid (SA) and γ-aminobutyric acid (GABA) are known to play roles in regulating plant stress responses. This study was conducted to determine metabolites and associated pathways regulated by ABA, SA and GABA that could contribute to drought tolerance in creeping bentgrass (Agrostis stolonifera). Plants were foliar sprayed with ABA (5 μ M), GABA (0.5 m M) and SA (10 μ M) or water (untreated control) prior to 25 days drought stress in controlled growth chambers. Application of ABA, GABA or SA had similar positive effects on alleviating drought damages, as manifested by the maintenance of lower electrolyte leakage and greater relative water content in leaves of treated plants relative to the untreated control. Metabolic profiling showed that ABA, GABA and SA induced differential metabolic changes under drought stress. ABA mainly promoted the accumulation of organic acids associated with tricarboxylic acid cycle (aconitic acid, succinic acid, lactic acid and malic acid). SA strongly stimulated the accumulation of amino acids (proline, serine, threonine and alanine) and carbohydrates (glucose, mannose, fructose and cellobiose). GABA enhanced the accumulation of amino acids (GABA, glycine, valine, proline, 5-oxoproline, serine, threonine, aspartic acid and glutamic acid) and organic acids (malic acid, lactic acid, gluconic acid, malonic acid and ribonic acid). The enhanced drought tolerance could be mainly due to the enhanced respiration metabolism by ABA, amino acids and carbohydrates involved in osmotic adjustment (OA) and energy metabolism by SA, and amino acid metabolism related to OA and stress-defense secondary metabolism by GABA. [ABSTRACT FROM AUTHOR]

Knowledge of heat‐responsive proteins is critical for further understanding of the molecular mechanisms of heat tolerance. The objective of this study was to compare proteins differentially expressed in two C3 grass species contrasting in heat tolerance, heat‐tolerant thermal Agrostis scabra and heat‐sensitive Agrostis stolonifera L., and to identify heat‐responsive proteins for short‐ and long‐term responses. Plants were exposed to 20/15°C (day/night, control) or 40/35°C (day/night, heat stress) in growth chambers. Leaves were harvested at 2 and 10 days after temperature treatment. Proteins were extracted and separated by fluorescence difference gel electrophoresis (DIGE). Thermal A. scabra had superior heat tolerance than A. stolonifera, as indicated by the maintenance of higher chlorophyll content and photochemical efficiency under heat stress. The two‐dimensional difference electrophoresis detected 68 heat‐responsive proteins in the two species. Thermal A. scabra had more protein spots either down‐ or up‐regulated at 2 days of heat stress, but fewer protein spots were altered at 10 days of heat stress compared with A. stolonifera. Many protein spots exhibited transient down‐regulation in thermal A. scabra (only at 2 days of heat treatment), whereas down‐regulation of many proteins was also found at 10 days of heat treatment in A. stolonifera, which suggested that protein metabolism in thermal A. scabra might acclimate to heat stress more rapidly than those in A. stolonifera. The sequences of 56 differentially expressed protein spots were identified using mass spectrometry. The results suggest that the maintenance or less severe down‐regulation of proteins during long‐term (10 days) heat stress may contribute to the superior heat tolerance in thermal A. scabra, including those involved in photosynthesis [RuBisCo, RuBisCo activase, chloroplastic glyceraldehydes‐3‐phosphate dehydrogenase (GAPDH), chloroplastic aldolase, oxygen‐evolving complex, photosystem I subunits], dark respiration (cytosolic GAPDH, cytoplasmic aldolase, malate dehydrogenase, hydroxypyruvate reductase, sedoheptulose‐1,7‐bisphosphatase), photorespiration [(hydroxypyruvate reductase, alanine aminotransferase (AlaAT), hydroxymethyltransferase (SHMT), glycine decarboxylase (GDC)], as well as heat and oxidative stress protection [heat shock cognate (HSC) 70 and FtsH‐like protein]. [ABSTRACT FROM AUTHOR]

Agrostis palustris sods were grown sequentially in a controlled environment chamber at 20–10, 25–15, 30–20, 35–25, and 40–30°C day‐night temperature regimes. Leaves grown at 40–30°C contained 53% more ethanol soluble and 51% more water soluble carbohydrate than those grown at the 4 lower temperature regimes. The increase in ethanol and water soluble carbohydrate in leaves at 40–30°C could not be attributed to a blockage in translocation of photoassimilate to lower plants parts based on quantitative carbohydrate analyses on stem and stolon tissue. Manometric measurements of photosynthesis indicated that leaf blades grown at the five temperature regimes exhibited different rate capabilities when tested under non‐limiting light and carbon dioxide levels. Oxygen evolution increased directly with temperature from 20 to 40°C and was 8 to 11 fold greater than the rate of carbon dioxide evolution. Both quantitative and qualitative differences in the photosynthetic rate were postulated in the leaf blade tissue tested. The quantitative difference was attributed to a possible difference in the number of cells per unit area and their size. The qualitative difference was attributed to greater thermal stability of leaf proteins when plants were grown at supraoptimal temperatures. Manometric respiratory rate studies did not indicate similar differences in temperature response in leaf blade tissue grown at the five temperature regimes. The cause of decreased shoot growth at supraoptimal temperatures could not be attributed to decreased and limiting C‐6 carbohydrate synthesis. [ABSTRACT FROM AUTHOR]

Agrostis palustris turfs cut weekly at 1.3 cm were subjected to successive four‐week periods with day‐night temperature regimes of 20–10, 25–15, 30–20, 35–25 and 40–30°C. Plants grown at 40–30°C exhibited a growth character distinctly different from those grown at 20–10°C. They were more upright and bristle‐like in growth habit. The percentage dry weight of leaf blade tissue increased 67% and weight per unit area increased 53% between 20–10 and 40–30°C. Reduced leaf blade width was noted first at 30–20°C while leaf blade length reduction first occurred at 35–25°C. Weekly yields were significantly reduced at the supraoptimal temperature regimes of 35–25 and 40–30°C. Chlorophyll content was lowest at 20–10 and 40–30°C, the lowest and highest temperature regimes studied. Shoot density appeared to decrease under the 35–25°C regime, but no dead plants were observed. The apparent decrease in shoot density was attributed to the upright growth habit. Density decreased at 40–30°C upon death of individual plants. A community of grass plants maintained as a turf was found to change in form quite rapidly in response to temperature. [ABSTRACT FROM AUTHOR]

We compared the foliar antioxidant status of native Agrostis stolonifera L. communities growing at two distinct CO2-enriched sites of geothermal origin (E) and at a control field location with normal CO2. Compared to the control, plants from both E-sites showed an increased size of the GSH pool, essentially due to enhanced GSSG levels, and a consequent decrease in the ratio between reduced and oxidised glutathione forms. Such differences were maintained and even enhanced in the vegetatively-propagated progenies of control and E-plants, grown under both greenhouse conditions and normal CO2 levels. The above results confirmed previous observations on native and crop plants exposed to elevated CO2. It is therefore suggested that changes in the glutathione redox balance might be of adaptive significance under conditions of permanent exposure to high CO2. [ABSTRACT FROM AUTHOR]

The influence of temperature was studied in relation to nitrate reductase activity of creeping bentgrass (Agrostis palustris Huds. cv. 'Toronto') a cool season grass and bermudagrass (Cynodon dactylon L. cv. 'Tifgreen') a warm season grass. Maximum nitrate reductase activity of both species occurred at 20°C. The nitrate reductase level in bentgrass leaves was reduced when grown at 35°C while bermudagrass leaves were relatively unaffected. The activity per se of the bentgrass enzyme preparation was inhibited rather than synthesis of the enzyme. [ABSTRACT FROM AUTHOR]