Heat-shock response of the upper intertidal barnacle Balanus glandula: thermal stress and acclimation

In the intertidal zone in the Pacific Northwest, body temperatures of sessile marine organisms can reach 35 degrees C for an extended time during low tide, resulting in potential physiological stress. We used immunochemical assays to examine the effects of thermal stress on endogenous Hsp70 levels in the intertidal barnacle Balanus glandula. After thermal stress, endogenous Hsp70 levels did not increase above control levels in B. glandula exposed to 20 and 28 degrees C. In a separate experiment, endogenous Hsp70 levels were higher than control levels when B. glandula was exposed to 34 degrees C for 8.5 h. Although an induced heat-shock response was observed, levels of conjugated ubiquitin failed to indicate irreversible protein damage at temperatures up to 34 degrees C. With metabolic labeling, we examined temperature acclimation and thermally induced heat-shock proteins in B. glandula. An induced heat-shock response of proteins in the 70-kDa region (Hsp70) occurred in B. glandula above 23 degrees C. This heat-shock response was similar in molting and non-molting barnacles. Acclimation of B. glandula to relatively higher temperatures resulted in higher levels of protein synthesis in the 70-kDa region and lack of an upward shift in the induction temperature for heat-shock proteins. Our results suggest that B. glandula may be well adapted to life in the high intertidal zone but may lack the plasticity to acclimate to higher temperatures.