Effects of chilling on the expression of ethylene biosynthetic genes in Passe-Crassane pear (Pyrus communis L.) fruits.

摘要

Passe-Crassane pears require a post-harvest exposure to chilling temperatures for ethylene production and normal ripening. ACC synthase and ACC oxidase cDNA probes were isolated to evaluate the role of chilling on ethylene biosynthetic gene expression in pear. A 3-month chilling treatment at 0 鳦 strongly stimulated ACC oxidase activity, and to a lesser extent ACC synthase activity. The levels of mRNAs hybridizing to ACC synthase and ACC oxidase probes also increased dramatically. Fruit stored at 18鳦 immediately after harvest did not exhibit any of these changes, whilst fruit that had been previously chilled exhibited a burst of ethylene production associated with high activity of ACC oxidase and ACC synthase upon rewarming. ACC oxidase mRNA strongly accumulated in rewarmed fruits, while ACC synthase mRNA level decreased. The chilling-induced accumulation of ACC synthase and ACC oxidase transcripts was strongly reduced when ethylene action was blocked during chilling with 1-methylcyclopropene (1-MCP). Upon rewarming, ACC synthase and ACC oxidase transcripts rapidly disappeared in 1-MCP-treated fruits. A 5-week treatment of non-chilled fruits with the ethylene analogue propylene led to increased expression of ACC oxidase and to ripening. However, ethylene synthesis, ACC synthase activity and ACC synthase mRNAs remained at very low levels. TThese data indicate that ACC synthase gene expression is regulated by ethylene only during or after chilling treatment, while ACC oxidase gene expression canbe induced separately by either chilling or ethylene. Nucleotide sequence data reported here will appear in the EMBL/GenBank/DDBJ sequence databases under accession numbers X87097 and X87112.