GENE EXPRESSION AND INTERNAL FEEDBACK REGULATION OF ETHYLENE BIOSYNTHESIS IN RIPENING FRUITS

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Expression and internal feedback regulation of the genes related to ethylene biosynthesis during ripening in banana and tomato fruits were investigated.MA-ACS1 was the gene in banana fruit related to the ripening process and was inducible by exogenous ethylene. At the onset of climacteric, ethylene production increased greatly with a sharp peak concomitant with an increase in the accumulation of MA-ACS1 mRNA and then decreased rapidly. This sharp peak of ethylene production was accompanying a sharp peak of in vivo ACC oxidase activity. However, the level of MA-ACO1 transcripts remained high from the onset of climacteric to the fully ripe stage. This discrepancy between enzyme activity and gene expression of ACC oxidase was, at leastin part, due to reduced contents of ascorbate and ferrous, cofactors of the enzyme, during ripening.We examined extraction method for ACC synthase from banana pulp using polyethyleneglycol added buffer followed by acetone washing. The method gave a high ACC synthase activity in accordance with ethylene production throughout fruit ripening.A trasgenic tomato plants were obtained in which LE-EIL genes, a most down stream gene in ethylene signalings, were introduced into the plants.