Using the technique of differential hybridization screening, we have isolated the cDNAs for two low-molecular-mass heat-shock proteins and their corresponding genes, HSP17.4 and HSP18.2, from Arabidopsis thaliana. These two genes encode polypeptides that are 79.2% identical to each other with respect to amino acid sequence, and contain several overlapping sequences that are similar to the consensus sequences for the heat-shock elements (HSE) in Drosophila in the regions upstream from the promoters. The 5' region of the HSP18.2 gene has been fused, in frame, to the uidA gene from Escherichia coli which encodes beta-glucuronidase (GUS), and the product has been introduced into petunia by Agrobacterium-mediated transformation. We have demonstrated that the GUS activity in transformed petunia plants is enhanced by heat shock.