THE HEAT-SHOCK RESPONSE AND EXPRESSION OF HEAT-SHOCK PROTEINS IN WHEAT UNDER DIURNAL HEAT-STRESS AND FIELD CONDITIONS

The occurrence of heat-shock proteins (HSPs) in response to high tempe rature stress is a universal phenomenon in higher plants and has been well documented. However, in agriculturally important species, less is known about the expression of HSPs under natural environments. A revi ew of the heat-shock response in wheat (Triticum aestivum L.) is prese nted and recent results on the expression of wheat HSPs under diurnal stress and field conditions are reported. In the field experiment, nag leaf blade temperatures were obtained and leaf blades collected for n orthern blot analysis using HSP 16.9 cDNA as a probe. Temperatures of leaf blades ranged from 32 to 35 degrees C under the tested field cond itions at New Deal near Lubbock, Texas. Messenger RNAs encoding a majo r class of low molecular weight HSPs, HSP 16.9, were detected in all w heat genotypes examined. The results suggested that HSPs are synthesis ed in response to heat stress under agricultural production, and furth ermore, that HSPs are produced in wheats differing in geographic backg round. In the controlled growth chamber experiment, HSP expression in two wheat cultivars, Mustang (heat tolerant) and Sturdy (heat suscepti ble) were analysed to determine if wheat genotypes differing in heat t olerance differ in in vitro HSP synthesis (translatable HSP mRNAs) und er a chronic, diurnal heat-stress regime. Leaf tissues were collected from seedlings over a time-course and poly (A)(+) RNAs were isolated f or in vitro translation and 2-D gel electrophoresis. The protein profi les shown in the 2-D gel analysis revealed that there were not only qu antitative differences of individual HSPs between these two wheat line s, but also some unique HSPs which were only found in the heat toleran t line. This data provides evidence of a correlation between HSP synth esis and heat tolerance in wheat under a simulated field environment a nd suggests that further genetic analysis of HSPs in a segregating pop ulation is worthy of investigation. In conclusion, the results of this study provide an impetus for the investigation of the roles of HSP ge nes in heat tolerance in wheat.