HEAT-SHOCK PROTEIN GENE-EXPRESSION IN DIPLOID WHEAT GENOTYPES DIFFERING IN THERMAL TOLERANCE

Under high temperature stress, plants synthesize a set of proteins called heat-shock proteins (HSPs). The objective of this research was to investigate HSP gene expression in two diploid wheat (Triticum monococcum L., 2n = 2x = 14) genotypes differing in thermal tolerance. Genotypes M3 (tolerant) and M9 (susceptible) were determined to be significantly different in acquired thermal tolerance based on the following criteria: reduction in regrowth during recovery from heat stress, reduction in chlorophyll content, and 2,3,5,-triphenyltetrazolium chloride reduction after 12 h of heat hardening prior to a normally lethal heat treatment. Electron micrographs revealed that the cellular ultrastructure of M3 was more thermally stable than that of M9 after only 2 h of heat hardening prior to a normally lethal heat treatment. Two-dimensional analysis of in vitro translated heat shock proteins revealed no observable qualitative differences in the HSP profile between the two genotypes. Northern analysis using HSP cDNAs 16.9, 26, and 70 as probes, indicated that M3 had higher steady state levels of HSP mRNA than M9 during the 2-h heat hardening. The results suggest that acquired thermal tolerance in wheat is correlated with the level of heat-shock gene expression during the first 2 h heat stress.