Heat Stress Effects on Protein Synthesis and Exosmosis of Cell Solutes in Three Turfgrass Species 1

Kentucky bluegrass ( Poa pratensis L.), annual bluegrass ( Poa annua L.), and perennial ryegrass ( Lolium perenne L.) differ in their heat tolerance as determined by plant dry weight 2 weeks after exposure to heat stress. The status of the plants at that time depends on the degree of injury that occurs during the stress treatment and the repair or tolerance of that injury. The purpose of this research was to evaluate species differences in the degree of initial injury due to heat stress. The incorporation of radio‐labeled leucine as an indicator of the net rate of protein synthesis and the efflux of cell solutes from plant tissue sections into distilled water were evaluated immediately after turfgrass shoots or tissue sections were exposed to temperatures in the range of 43 to 51 °C for 30 min. Net protein synthesis in the grasses was very heat labile. Incorporation of radiolabeled leucine declined an average of 69% in plants previously heated at 43 °C compared to plants held at 27 °C. Efflux of cell solutes from the tissue sections did not increase in plants that had been heated to 43, 45, 47, or 49 °C compared to plants held at 25 °C. No significant differences were found between the grasses for the parameters tested. Either disruption of some other physiological process or differential repair or tolerance of the heat stress injury accounted for the heat tolerance rankings of the grasses. Also, the results of this study indicate that indirect rather than direct heat injury is responsible for the behavior of the grasses stressed at the temperatures and exposure periods used in this study.