HEAT-SHOCK-PROTEIN EXPRESSION IN MYTILUS-CALIFORNIANUS - ACCLIMATIZATION (SEASONAL AND TIDAL-HEIGHT COMPARISONS) AND ACCLIMATION EFFECTS

Heat-shock protein (hsp) expression was examined in gill of field-accl imatized and laboratory-acclimated mussels (Mytilus californianus) fro m the Oregon coast. Endogenous levels of heat-shock proteins in the 70 -kDa class (hsp70 isoforms) and profiles of induction temperature for newly synthesized hsp70 were measured in freshly held-collected specim ens as functions of location height in the intertidal and season, and in mussels after 7 weeks of laboratory thermal acclimation. There were significant differences in endogenous levels of hsp70 as functions of season and collection height. Strong induction of new hsp70 synthesis occurred at body temperatures within the range measured in field spec imens. Profiles of hsp70 thermal induction varied significantly with s eason, but not with height of collection. In contrast to the large dif ferences in hsp70 expression between winter- and summer-acclimatized m ussels, no differences related to temperature occurred in the differen tly acclimated mussels. The differences found between the effects of f ield acclimatization and laboratory thermal acclimation suggest that t he stress response is modulated by environmental factors in addition t o body temperature. Thus, caution is required in extrapolating from la boratory acclimation studies to acclimatization effects in field popul ations. The seasonal and tidal-height variations in the heat-shock res ponse are discussed in the context of energy costs of protein turnover .