Changes of lipid composition and saturation level in leaves and roots for heat-stressed and heat-acclimated creeping bentgrass (Agrostis stolonifera)

Changes in membrane lipid compositions and saturation levels during high temperature acclimation and heat stress were investigated in leaf and root tissues for three cultivars of creeping bentgrass (Agrostis stolonifera) that differ in heat tolerance. 'L-93' (heat tolerant), 'Penncross' (heat sensitive) and 'Crenshaw' (intermediate) showed differential decreases in grass visual quality (leaf color and shoot density), increases in TBARS (a measure of oxidative damage), increases in membrane leakage and decreases in chlorophyll content of leaves during 28 days of heat stress (35 °C) in a growth chamber study. Total lipid extracts from the leaves of all three cultivars showed that the lipid saturation level increased over time under heat stress, with the change being predominantly due to decreases in linolenic acid and increases in linoleic and palmitic acids. The only significant difference in leaf lipid saturation between the three cultivars was that L-93 extracts contained a higher proportion of saturated lipids prior to heat stress than the other two cultivars. No cultivar differences in lipid composition were detected during heat stress. Penncross plants given a mild heat pre-treatment (30 °C) (heat acclimated) prior to being exposed to heat stress (35 °C) showed increased saturation of leaf lipids at the initiation of heat stress. There were no significant differences in root lipid composition between heat-acclimated and non-acclimated plants. Penncross plants which had acquired thermotolerance through heat acclimation, and heat tolerant L-93 plants showed similar leaf lipid composition at the initiation of heat stress, and similar levels of thermotolerance during heat stress. These results imply that there may be some connection between the degree of saturation of leaf membrane lipids prior to heat stress and the ability of that plant to limit heat-induced damages during the stress period. Root lipid extracts from the three cultivars showed no change in saturation levels during heat stress. However, Penncross root extracts contained a lower proportion of saturated lipids than L-93 or Crenshaw. These results suggest that lipid composition or saturation level of roots could be an important factor in controlling plant tolerance to heat stress.