ANALYSIS OF HEAT-SHOCK RESPONSE IN PERENNIAL RYEGRASS USING MAIZE HEAT-SHOCK PROTEIN CLONES

Evidence suggests that heat shock proteins (HSP) may be involved in differences in thermal tolerance among perennial ryegrass (Lolium perenne L.) cultivars. It seems possible that HSP could be useful in developing laboratory assays for thermal tolerance in perennial ryegrass. To evaluate the possibility of using HSP genes or gene products to screen for thermal tolerance, thermal-tolerant and thermal-sensitive cultivars were germinated and heat treatments were conducted in a dry germinator in constant light. The two cultivars exhibited differences in root, shoot, and total seedling length when briefly subjected to high temperatures (55 degrees C) following an initial acclimation period (40 degrees C). In vitro translation products of total RNA indicated that different messenger RNA (mRNA) populations were present in seedlings exposed to stress temperatures. Hybridizations of two maize (Zea mays L.) heat shock clones, pMON9501 (HSP 70) and pZmHSP26 (HSP 26), to genomic DNA indicated a high degree of homology between the two perennial ryegrass cultivars and the HSP 70 clone and a moderate homology of the cultivars with BSP 26. The HSP 70 clone revealed restriction fragment length polymorphisms between the cultivars. Hybridizations of the two maize heat shock clones to Northern blots with perennial ryegrass total RNA showed that HSP 70 and HSP 26 mRNA were heat inducible. There were detectable differences in the levels of heat-induced HSP 26 mRNA between the two cultivars. Our findings indicated that analysis of HSP could provide the basis of a rapid and reliable characterization of thermal tolerance in perennial ryegrass.