Expression Patterns of Heat Shock Proteins in Relation to Heat Stress Tolerance of Creeping Bentgrass Treated with Cytokinin and Nitrate.

Heat stress is a primary factor in summer bentgrass decline. Preliminary data suggest that combining exogenous cytokinin and nitrogen may improve creeping bentgrass (Agrostis stolonifera L.) heat tolerance. Changes in gene expression at the transcriptional and/or translation level are thought to be a fundamental mechanism in plant response to environmental stresses. Heat stress redirects protein synthesis in higher plants and results in a nearly exclusive synthesis of stress proteins, particularly heat shock proteins (HSPs). The goal of this work was to analyze the pattern of expression of the major members of the HSP group in creeping bentgrass during different heat stress periods, and then to study the influence of cytokinin and nitrogen on the expression pattern of HSPs. A growth chamber study on ‘Penn-A4’ creeping bentgrass subjected to 35/28 ^oC, day/night was conducted with three nitrate rates (0, 2.5, and 7.5 kg N ha^-1 and three cytokinin concentrations of zeatin riboside (tZR, 0, 10 and 100 μM) all applied biweekly. Green color index (NDVI), photochemical efficiency (Fv/m), shoot electrolyte leakage (EL) and root viability (RV) were monitored, along with the expression pattern of HSPs using western blot. There was no difference in measured parameters between treatments until week 16, except EL at week 6. At week 16, EL ranged from 28% to 45%, and RV was from 0.13 to 0.56. HSP70 expression was increased at high N regardless of CK rates. Bentgrass receiving no supplemental nitrogen or CK had the least amount of HSP70 expression. This study could further improve our understanding of the role of specific HSPs in heat tolerance of creeping bentgrass, especially in terms of understanding the interactive effects of exogenous nitrogen and cytokinin.