GENE-EXPRESSION DURING COLD AND HEAT-SHOCK IN WHEAT

Translatable messenger RNAs expression was compared in cold- and heat-stressed winter wheat (Triticum aestivum L. 'Fredrick' and 'Norstar') and spring wheat (T. aestivum L. 'Glenlea'). Polyadenylated RNA isolated from the crown and leaf tissues was translated in a wheat germ cell free system and the acidic and basic in vitro products were resolved by two-dimensional SDS-PAGE and autoradiography. The results showed that low temperature stress rapidly induced two groups of mRNAs. The first group was transient in nature and consists of 18 mRNAs that reached their highest levels of induction after 24 h of low temperature exposure and then decreased to undetectable levels. The second group consists of 53 mRNAs that were also induced or increased rapidly, but maintained their levels of expression during the 4 weeks required to induce freezing tolerance. Among those, at least 34 were expressed at higher levels in the freezing tolerant winter wheat compared with the less tolerant spring wheat. This suggests a possible relation between the expression of these mRNAs and the capacity of each genotype to develop freezing tolerance. In the case of heat shock, 50 mRNAs were induced or increased after 3 h at 40-degrees-C. Among these, the expression of only six mRNAs was altered in a similar manner in the three genotypes by both treatments. The remaining mRNAs code for typical heat shock proteins which are different from those induced by low temperature. None of these mRNAs has been associated with the development of freezing tolerance. These results suggest that heat and cold stress are controlled by different genetic systems.