Effect of low‐temperature rearing on heat shock protein synthesis and heat sensitivity in Drosophila melanogaster

The patterns of synthesis of heat shock proteins (hsp) and heat sensitivity to elevated temperatures in larvae of Drosophila melanogaster reared since hatching at 20°C (warmreared) or at 10°C (cold‐reared) were compared. The pattern of hsp synthesis in salivary glands from the cold‐ and warm‐reared late‐third‐instar larvae exposed for l hr to 33°C or to 37°C was generally similar except for remarkable differences in the 23 kd hsp and a heat‐inducible 14 kd polypeptide. The hsp 23 was abundantly synthesised in control as well as heat‐shocked warm‐reared larval salivary glands, its synthesis in heat‐shocked glands being dependent on new transcription. The synthesis of hsp 23 was much less in control glands of cold‐reared larvae and was not further inducible by heat shock. The 14 kd polypeptide synthesis was greater in control as well as heat‐shocked salivary glands of cold‐reared larvae, whereas, in the warm‐reared ones, its activity was much less. The cold‐reared larvae showed greater sensitivity to elevated temperature; fewer adults eclosed when the cold‐reared late‐third‐instar larvae were exposed to 40°C for l hr and also a pretreatment at 37°C for l hr was less effective in stopping the killing effect of a subsequent 40°C heat shock in cold‐reared than in warmA‐reared larvae. The greater thermosensitivity of the cold‐reared larvae may be correlated with the altered patterns of heat shock gene transcription and translation in cold‐reared larvae.