molecular analysis of mechanism of fruit ripening and softening in pears

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In order to establish physiological base of postharvest technology for extended shelf life with better quality, we investigated the mechanism of fruit ripening and softening at molecular level. We isolated ethylene biosynthetic gene (four isogenes for ACC synthase and two isogenes for ACC oxidase) and genes encoding cell wall modifying (two isogenes for polygalacturonase, two isogenes for cellulase and eight isogenes for expansin). The ripening ethylene production declined with decrease of transcripts for ACC synthase and ACC oxidase by 1-MCP, a strong inhibitor of ethylene action when it was applied to fruit after onset of climacteric ethylene. The results indicate that ripening ethylene biosynthesis in pear fruit is regulated in positive feedback manner. In addition of suppression of ethylene biosynthesis, 1-MCP application during ripening stage significantly delayed the subsequent fruit softening, resulting in extended shelf life more than twice of non-treated fruit. In the 1-MCP treated fruit the expression of three isogenes for expansin and two for polygalacturonase was suppressed while other members of expansin and two cellulase genes were not affected. These results suggest that expression of some expansin and polygalacturonase genes depends on ethylene and plays an important role in fruit softening. We concluded that application of 1-MCP and metabolic engineering of ethylene biosynthetic gene such as ACC synthase and ACC oxidase promise advanced postharvest technology in transportation and marketing in pear fruit.