INDUCTION TEMPERATURE OF HEAT-SHOCK PROTEIN-SYNTHESIS IN WHEAT

The adverse effects of heat stress are a major limitation to realizing the genetic potential for productivity of wheat (Triticum aestivum L.). This study was undertaken to characterize the temperature-dependent induction response of heat-shock protein (HSP) synthesis in wheat seedlings, and to determine if HSPs could be detected in flag leaves of flowering wheat plants at nonlethal temperatures similar to those encountered during agricultural production. The HSP profile was characterized by isoelectric focusing and polyacrylamide gel electrophoresis of S-35-methionine labeled products of an in vitro translation of poly (A)+ RNA obtained from seedling leaf blades exposed to temperatures of 22, 25, 28, 31, 34, and 37-degrees-C for 2 h and in flag leaf blades exposed to 32-degrees-C for 2 h. Synthesis of HSPs was detected in seedling leaf tissue during heat shock between 28 and 31-degrees-C and in flag leaves at 32-degrees-C. This observation in seedlings was confirmed by northern blot analysis utilizing HSP 16.9 and HSP 70 P-32-labeled probes. These results indicate that both low and high molecular weight HSPs are synthesized in wheat as a response to heat stress when leaf temperatures increase almost-equal-to 10-degrees-C above the optimal growth temperature of 18 to 23-degrees-C. Detection of low and high molecular weight HSPs synthesized in seedlings and flag leaves of flowering plants suggests that HSPs are synthesized before leaf temperatures reach levels that are considered injurious to growth and development.