Stress Responses in Cell Cultures of Lolium temulentum. II. Induction of Thermotolerance and Associated Changes in Gene Expression

Abstract

Summary The induction and longevity of thermotolerance has been assessed in cell cultures of Lolium temulentum and changes in gene expression associated with thermotolerance determined. More than 15 minutes at 37 °C was required to induce thermotolerance in these cell cultures, with the highest levels of thermotolerance being obtained with a one hour, 37 °C conditioning heat shock treatment. Increasing the conditioning heat shock to two hours at 37 °C resulted in a fall in the level of induced thermotolerance. Thermotolerance could not develop at 37 °C but required a recovery period at 25 °C for more than one hour before the non-permissive heat shock. Short incubations at 45 °C were incapable of rendering the cells thermotolerant, even with a recovery period. Thermotolerance persisted for at least 24 hours, but had disappeared by 48 hours. Replicate cultures which were, or were not, thermotolerant were analysed by in vitro translation of isolated RNAs. The major differences were a decrease in the levels of a number of hsp mRNAs, and a more rapid return to pre-heat shock levels of control mRNAs in thermotolerant cells.