HEAT-SHOCK PROTEINS DO NOT PROVIDE THERMOPROTECTION TO NORMAL CELLULAR PROTEIN-SYNTHESIS, ALPHA-AMYLASE MESSENGER-RNA AND ENDOPLASMIC-RETICULUM LAMELLAE IN BARLEY ALEURONE LAYERS

Heat shock in barley (Hordeum vulgare L. cv. Himalaya) aleurone layers induces the synthesis of heat shock proteins (hsps) and suppresses th e synthesis and secretion of alpha-amylase, the principal secretory pr otein. This is accompanied by the destabilization of alpha-amylase mRN A and a concomitant dissociation of ER lamellae. In the absence of hea t shock alpha-amylase mRNA is extremely stable (Belanger et al. 1986. Proc. Natl. Acad. Sci. USA 83: 1354-1358). In most organisms there is a direct correlation between the synthesis of hsps and thermotolerance . The ability of hsps to provide thermoprotection to secretory protein synthesis, alpha-amylase mRNA and ER lamellae was analyzed. Sodium do decyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of pulse-c hased, [S-35]-methionine-labeled proteins revealed that the half-life of hsps in barley aleurone cells recovering from heat shock was approx imately 12 h. Within approximately 6 h, there was a recovery of alpha- amylase mRNA and a reformation of ER lamellae. Heat shock protein synt hesis was induced by either heat shock (40 degrees C) or arsenite, the cells were allowed to recover for S h, then were re-exposed to heat s hock. Results from SDS-PAGE showed that, despite the presence of hsps, alpha-amylase synthesis was suppressed. Northern blot hybridizations showed that alpha-amylase mRNA levels were reduced in heat-shocked tis sues. Transmission electron microscopy demonstrated that ER lamellar s tructures were dissociated. The synthesis of hsps did not enable barle y aleurone cells to sustain the synthesis of any proteins at lethal te mperature. In contrast, similar conditions established thermotolerance and provided thermoprotection to protein synthesis in germinating bar ley embryos. Our findings suggest that the aleurone layer does not bec ome thermotolerant following the induction of hsp synthesis.