HEAT-SHOCK TEMPERATURE-ACCLIMATION OF NORMAL SECRETORY PROTEIN-SYNTHESIS IN BARLEY ALEURONE CELLS

Exposure of barley (Hordeum vulgare L. cv. Himalaya) aleurone layers t o 40 degrees C for a period of 3 h results in the selective suppressio n of the synthesis and secretion of hydrolytic enzymes; other normal c ellular protein synthesis continues during heat shock, This suppressio n is correlated with secretory protein mRNA destabilization and the di ssociation of stacked ER lamellae during heat shock (Belanger et al. 1 986, Proceedings of the National Academy of Sciences USA 83, pp, 1354- 1358), In this report we examined the effect of exposure to extended p eriods of heat shock, If exposure to 40 degrees C was continued for a period of 18 h, the synthesis of alpha-amylase, the predominant secret ed hydrolase,resumed, This was accompanied by increased alpha-amylase mRNA levels and the reformation of ER lamellae, Though initial exposur e (3 h) to 40 degrees C reduced protein secretion to approximate to 10 % of that observed in aleurone cells maintained at 25 degrees C, expos ure for prolonged periods (16-20 h) permitted the resumption of protei n secretion to approximate to 66% of non-heat-shocked control levels, The resumption of normal secretory protein synthesis during prolonged exposure to 40 degrees C was correlated with an increase in the incorp oration of [C-14]glycerol into phosphatidylcholine and an increase in the ratio of saturated to unsaturated fatty acids in lipids isolated f rom ER membrane preparations, Increased fatty acid saturation has been demonstrated to enhance thermostability in biological membranes, and such changes in membrane composition may be important to the recovery of secretory protein synthesis at the ER.