STRESS RESPONSES IN CELL-CULTURES OF LOLIUM-TEMULENTUM .2. INDUCTION OF THERMOTOLERANCE AND ASSOCIATED CHANGES IN GENE-EXPRESSION

The induction and longevity of thermotolerance has been assessed in ce ll cultures of Lolium temulentum and changes in gene expression associ ated with thermotolerance determined. More than 15 minutes at 37 degre es C was required to induce thermotolerance in these cell cultures, wi th the highest levels of thermotolerance being obtained with a one hou r, 37 degrees C conditioning heat shock treatment. Increasing the cond itioning heat shock to two hours at 37 degrees C resulted in a fall in the level of induced thermotolerance. Thermotolerance could not devel op at 37 degrees C but required a recovery period at 25 degrees C for more than one hour before the non-permissive heat shock. Short incubat ions at 45 degrees C were incapable of rendering the cells thermotoler ant, even with a recovery period. Thermotolerance persisted for at lea st 24 hours, but had disappeared by 48 hours. Replicate cultures which were, or were not, thermotolerant were analysed by in vitro translati on of isolated RNAs. The major differences were a decrease in the leve ls of a number of hsp mRNAs, and a more rapid return to pre-heat shock levels of control mRNAs in thermotolerant cells.