Mechanism of fruit softening and its inhibition during distribution and storage in persimmon fruit

梨果实采后软化过程中细胞壁发生强烈的变化。为了探讨果实软化的机理，本研究采用了乙烯作用的强抑制剂1-MCP，并利用分子生物学技术对果实软化机理进行了研究。首先，我们克隆了柿果实ACC合成酶、ACC氧化酶、纤维素酶（Cel）、多聚半乳糖醛酸酶（PG）和膨胀素（expansin）的cDNA，并对其表达进行了分析，结果表明，在柿果实采收后的几天内，乙烯的产生在所有组织中均被诱导，同时伴随着所有DK-ACS和DK-ACO基因在时间和空间上的协调表达。在除花萼外的所有组织中，1-MCP处理抑制乙烯产生和乙烯生物合成相关基因的表达。然而，在花萼中，DK-ACS 2表现出增加的mRNA积累，伴随着大量的乙烯产生，1-MCP处理不能阻止这些事件。此外，通过包装的水分胁迫的缓解， ...更多信息 结果表明，套袋处理显著延迟了乙烯的产生和DK-ACS 2在花萼中的表达。这些结果表明，柿果实中乙烯的生物合成最初是在花萼中诱导的，并通过DK-ACS 2的转录激活受到水分损失的调节。结果表明，在采收后的“平种梨”柿果实中，DK-Cel 3、DK-PG 1和DK-Exp 2 mRNA的积累与乙烯的产生和软化同时进行。MCP预处理延迟了这些mRNA的积累和果实软化，而丙烯处理导致这些mRNA在一天内积累和果实快速软化。另一方面，DK-Cell、DK-Cel 2和DK-Exp 1的mRNA在收获时已经在果实中积累，并在货架期内减少。这些结果表明，DK-Cel 3、DK-PG 1和DK-Exp 2的乙烯依赖性基因表达可能与“平种梨”果实软化密切相关。我们研究了1-MCP与高CO2脱涩处理相结合延长“远早”和“西条”果实货架期的商业应用潜力。非1-MCP处理的果实在收获后5天内软化，导致不可接受的品质。1-MCP处理<-1>16 - 48 h，在室温下，对采后12天和16天的果实软化分别有抑制作用。从收获到1-MCP处理开始的长达12小时的时间滞后并没有损害1-MCP的有益效果。这些结果表明，1-MCP是一种很有前途的化学品，以延长日本柿货架期。少

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 … More 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