| Research Abstract |
Persimmon fruit undergoes intensive cell wall modification during fruit softening in its postharvest life. In order to investigate the mechanism of fruit softening, we employed a strong inhibitor of ethylene action, 1-MCP, and the technique of molecular biology. As the first step, we cloned cDNAs for ACC synthase, ACC oxidase, cellulase (Cel), polygalacturonase (PG) and for expansin, from persimmon fruit and characterized their expression.
Ethylene production was induced within a few days of harvest in all fruit tissues tested, accompanied by temporally and spatially coordinated expression of all the DK-ACS and DK-ACO genes. In all tissues except the calyx, treatment of 1-MCP suppressed ethylene production and ethylene biosynthesis-related gene expression. In the calyx, however, DK-ACS2 exhibited increased mRNA accumulation accompanied by a large quantity of ethylene production, and 1-MCP treatment did not prevent the events. Furthermore, the alleviation of water stress by packaging the
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fruit with perforated polyethylene bag significantly delayed the onset of ethylene production and the expression of DK-ACS2 in the calyx. These results indicate that ethylene biosynthesis in persimmon fruit is initially induced in calyx and is modulated by water loss through transcriptional activation of DK-ACS2. The ethylene produced in the calyx subsequently diffuses to other fruit tissues and acts as a secondly signal that stimulates autocatalytic ethylene biosynthesis in these tissues, leading to intensive fruit softening.
The accumulation of DK-Cel3, DK-PG1, and DK-Exp2 mRNAs was induced simultaneously with commencement of ethylene production and softening in harvested 'Hiratanenashi' persimmon fruit. The MCP pre-treatment delayed the accumulation of these mRNAs and fruit softening while propylene treatment resulted in the accumulation of these mRNAs within one day and a rapid fruit softening. On the other hand, mRNAs for DK-Cell, DK-Cel2, and DK-Exp1 had already accumulated in the fruit at harvest and decreased during shelf life. These results indicate that the ethylene dependent gene expression of DK-Cel3, DK-PG1, and DK-Exp2 might be closely involved in fruit softening of 'Hiratanenashi' persimmon.
We investigated the potential for commercial use of 1-MCP to extend the shelf life of 'Tonewase' and 'Saijo' fruit, in combination with de-astringency treatment using high carbon dioxide. The non-1-MCP treated fruits softened within 5 days after harvest, resulting in unacceptable quality. The 1-MCP treatments at more than 100 nl 1^<-1> for 16 -48 h inhibited fruit softening for 12 days and 16 days after harvest at room temperature in 'Tonewase' and 'Saijo', respectively. A time lag of up to 12 h from harvest to the beginning of 1-MCP treatment did not damage the beneficial effects of 1-MCP. These results indicate that 1-MCP is a promising chemical to extend shelf life of Japanese persimmons. Less
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