Heat shock response of warm-incubated barley aleurone layers

Heat shock suppresses secretory protein synthesis in GA(3)-stimulated barley (Hordeum vulgare cv. Himalaya) aleurone layers by selectively destabilizing their mRNAs and dissociating the stacked rough endoplasmic reticulum (ER) lamellae upon which they are translated. Heat shock also increases phosphatidylcholine (PC) synthesis, and these PC molecules have increased levels of fatty acid saturation. This appears to be adaptive, for aleurone layers maintained at heat shock temperatures for 18 h resynthesize secretory protein mRNAs, rebuild stacked ER lamellae, and resume secretory protein synthesis. In the present study aleurone layers were incubated at warmer than normal pre-heat shock temperatures to determine whether this would favor the formation of heat-resistant ER lamellae that could continue secretory protein synthesis during heat shock. Western blot and SDS-PAGE analyses showed that such treatment did not induce heat shock protein (HSP) synthesis, but it preserved significant secretory protein synthesis during heat shock. Northern hybridizations revealed that levels of mRNAs encoding secretory proteins were several-fold elevated as compared to 25°C preincubated controls, and transmission electron microscopic observations revealed stacked ER lamellae. Thin layer and gas chromatography showed that PC molecules in warm-incubated barley aleurone layers had more fatty acid saturation than did controls. These observations indicate that previous incubation temperature influences both the induction of HSP synthesis and the suppression of normal protein synthesis in the heat shock response. However, we found that it does not affect the temperature at which heat shock becomes lethal.