THE SYNTHESIS OF HSPS IN SUGAR-BEET SUSPENSION-CULTURE CELLS UNDER HYPERTHERMIA EXHIBITS DIFFERENTIAL SENSITIVITY TO CALCIUM

Experiments aimed at testing the effect of Ca2+ on heat shock-induced changes in protein synthesis of cultured sugar beet cells were perform ed. Heat shock inhibits the synthesis of non-heat shock proteins (non- HSPs) and promotes the synthesis of a set of HSPs. Extracellular Ca2appeared to be strictly required for the synthesis of non-HSPs. Calciu m was found to differentially exert its effect on the HSP synthesis: c alcium induced (96 and 76 kDa), stimulated (94, 67, 58, 52, 32, 30, 26 and 22 kDa) or did not influence (82, 17 kDa) the de novo production of various HSPs. Cell injury increased if the cells were exposed to hi gh temperature in a Ca2+-deficient medium. Calcium supplement to Ca2+- depleted cells resulted in the recovery of HSP synthesis and reduced c ell injury by heat shock.