Reduction of chilling injury and transcript accumulation of heat shock proteins in tomato fruit by methyl jasmonate and methyl salicylate

Abstract

Changes in heat shock protein (HSP) gene expression induced by vapor application of methyl jasmonate (MeJA) and methyl salicylate (MeSA) in tomato fruit were investigated and compared to the well-described heat shock response. Northern hybridization experiments involving six cDNAs, encoding class I and II tomato small HSPs (sHSPs) and three members of HSP 70 family, showed that accumulation of class I and II sHSP mRNAs was increased significantly by MeJA and MeSA. When the treated fruits were transferred to low temperature, class I and II mRNA levels initially decreased, but then subsequently increased. Accumulation of HSP transcripts was also observed in non-treated fruit between 7 and 14 days at low-temperature storage, but all decreased to undetectable levels after 21 days. Following MeJA and MeSA treatments, the transcripts of HSP 70 family accumulated to higher levels than following the heat treatment. MeJA- and MeSA-treatments were clearly shown to alleviate chilling injury (CI), whereas tomato fruit stored at 5 °C without pretreatment developed typical symptoms and severe decay. These results demonstrated that MeJA and MeSA induced the accumulation of sHSP transcripts in tomato. The increased transcript abundance of HSPs, especially class II sHSPs, was correlated with protection against CI.