Induced thermotolerance and associated expression of the heat-shock protein Hsp70 in adult Drosophila melanogaster

1. Inducible heat-shock proteins are synthesized when temperatures are incr eased to levels substantially above normal. The functional role of these pr oteins is well known at the cellular level. Today increasing interest has b een directed towards the importance of heat-shock proteins for resistance o f whole organisms to high-temperature stress and other environmental stress ors. 2. Here the functional relationship between the heat-shock protein, Hsp70, and thermal resistance in adult Drosophila melanogaster was examined by com paring thermal resistance, i.e, survival at 39 degrees C for 85 min, and le vels of Hsp70 at various times elapsed (2, 4, 8, 16, 32 and 64 h) after the rmotolerance was induced by short-term accrimation/heat hardening at 37 deg rees C for 55 min. 3. Levels of Hsp70 in both males and females were highest 2 h after heat ha rdening and declined with longer times elapsed. The rate of decrease initia lly was very fast but diminished with increasing time. After 32 h the level of Hsp70 approached the level in flies that were not hardened. Levels of H sp70 in males exceeded that of females during the entire period. 4. Survival of both sexes increased with increasing time after heat hardeni ng and reached an optimum between 8 and 32 h. Thereafter resistance decreas ed with longer times elapsed. Survival of females generally exceeded that o f males except after 16 and 64 h. 5. Regression analysis applied to the data on Hsp70 levels revealed that th e model describing these data could not explain the data for survival. Also , higher levels of Hsp70 in males compared with females were not associated with greater survival in males. However, statistical analysis on paired me asurements of Hsp70 and survival revealed a positive association between Hs p70 level and survival at each time elapsed after induction of thermotolera nce.