THERMOTOLERANCE AND HEAT-SHOCK PROTEINS IN CHIRONOMUS

The acquisition of thermotolerance in Chironomus thummi has been analysed. When larvae were subjected to 15 min exposure at 40-degrees-C, over 90% of larvae died a few hours later. Under these conditions, no heat shock protein synthesis could be detected in cells from larvae tissues. If a conditioning treatment (35-degrees-C 1 h) was given prior to the test treatment, the larvae were thermotolerant between 3-72 h after the conditioning treatment. The optimal post-test treatment level of survival was reached at 8-24 h after the conditioning treatment. When thermotolerance was induced, the cells acquired the ability to synthesize heat shock proteins after the second heat exposure. This second synthesis took place during the recovery period and also occurred if a carbon dioxide treatment was applied as the conditioning treatment. If heat shock protein synthesis was inhibited by blocking transcription with Actinomycin-D (AMD) it was also possible to induce thermotolerance, but with some differences: the posterior survival was restricted to 24-48 h after test treatment. Actinomycin-D itself could induce the same state of thermotolerance. Our data indicate that it is possible to induce thermotolerance in C. thummi which can then be expressed as two different types of survival: a short-term survival achieved independently of heat shock protein synthesis, and a long-term survival which seems to be connected with the synthesis of heat shock proteins after the second treatment.