Expression of a water stress-induced polygalacturonase gene in harvested cucumber fruit

We investigated the molecular response of harvested cucumber (Cucumis sativ us L.) fruit to postharvest water stress. Using RT-PCR, we isolated CUPG1 c DNA, a cDNA clone encoding polygalacturonase (PG) that is inducible by wate r stress in cucumber fruit and characterized the expression of the gene wit h respect to hormonal control. The full length sequence determined by RACE- PCR, encoded a deduced protein of 435 amino acids that contained several co mmon conserved domains as reported for PGs. The CUPG1 gene expression was a lso induced by exogenous ethylene but not by the application of abscisic ac id (ABA). The level of CUPG1 mRNA induced by water stress, was reduced by 5 0% in fruits pre-treated with 1-methyl-cyclopropene (MCP), a strong inhibit or of ethylene action, which suggests that the expression of CUPG1 gene cou ld be induced by a direct mechanism through water stress and an indirect me chanism mediated through ethylene produced in response to water stress. We conclude that water loss in harvested cucumber fruit results not only in ph ysical changes but also leads to molecular responses, including PG gene exp ression.