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 di fferences in thermal tolerance among perennial ryegrass (Lolium perenn e L.) cultivars. It seems possible that HSP could be useful in develop ing 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 cultiva rs were germinated and heat treatments were conducted in a dry germina tor in constant light. The two cultivars exhibited differences in root , shoot, and total seedling length when briefly subjected to high temp eratures (55 degrees C) following an initial acclimation period (40 de grees C). In vitro translation products of total RNA indicated that di fferent messenger RNA (mRNA) populations were present in seedlings exp osed to stress temperatures. Hybridizations of two maize (Zea mays L.) heat shock clones, pMON9501 (HSP 70) and pZmHSP26 (HSP 26), to genomi c DNA indicated a high degree of homology between the two perennial ry egrass cultivars and the HSP 70 clone and a moderate homology of the c ultivars with BSP 26. The HSP 70 clone revealed restriction fragment l ength polymorphisms between the cultivars. Hybridizations of the two m aize heat shock clones to Northern blots with perennial ryegrass total RNA showed that HSP 70 and HSP 26 mRNA were heat inducible. There wer e detectable differences in the levels of heat-induced HSP 26 mRNA bet ween the two cultivars. Our findings indicated that analysis of HSP co uld provide the basis of a rapid and reliable characterization of ther mal tolerance in perennial ryegrass.