Abstract
The hypothesis that heat shock induces systemic acquired resistance (SAR) was supported by an analysis of salicylic acid (SA) content and the expression of a SAR related gene, CuPil, in cucumber. Twenty-two cultivars of cucumber were exposed to heat shock at maximum 45°C for 1 hr every day from July 7 till Sept. 14. The SA content in leaves was estimated using capillary electrophoresis. The SA content increased much more in heat-shocked leaves than in non-treated leaves in 18 varieties. However, there was no correlation between SA content and heat sensitivity in the heat tolerance test using chlorophyll fluorescence. To prove that SA induced by heat shock acts as a SAR signal transducer, the expression of CuPil, a SAR related gene, was traced using a RT-PCR-based assay. CuPil mRNA was expressed after heat shock. In conclusion, SAR appeared to be induced by heat shock without chemical inducers or infection. It is suggested that heat shock should be useful for inducing SAR.
