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

柿果实在采后软化过程中经历了密集的细胞壁修饰。为了研究果实软化的机理，我们采用了一种强的乙烯作用抑制剂1-MCP，并利用分子生物学技术。作为第一步，我们从柿果实中克隆了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，并对它们的表达进行了研究。在除花萼外的所有组织中，1-MCP处理抑制了乙烯的产生和乙烯生物合成相关基因的表达。然而，在花萼中，DK-ACS2表现出增加的mRNA积累伴随着大量的乙烯产生，而1-MCP处理并不能阻止这一过程。此外，通过包装…来缓解水分胁迫聚乙烯袋穿孔果实的增多显著推迟了乙烯的产生和DK-ACS2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-ACS2的转录激活而受到失水的调控。花萼中产生的乙烯随后扩散到其他果实组织，作为第二信号刺激这些组织中自催化乙烯的生物合成，导致果实严重软化。‘平山柿’果实在开始乙烯产生和软化的同时，诱导了DK-Cel3、DK-PG1和DK-Exp2mRNAs的积累。MCP处理延缓了这些mRNAs的积累和果实软化，而丙烯处理则导致这些mRNAs在一天内积累，果实软化迅速。另一方面，DK-Cell、DK-Cel2和DK-Exp1的mRNAs在采收时已在果实中积累，并在货架期下降。这些结果表明，DK-Cel3、DK-PG1和DK-Exp2的乙烯依赖基因表达可能与‘Hiratanenashi’果实软化密切相关。我们研究了1-MCP在延长‘Tonewase’和‘Saijo’果实货架期方面的商业应用潜力，并结合高二氧化碳脱涩处理。未经1-MCP处理的果实在采收后5天内软化，品质不佳。在室温条件下，1-MCP浓度超过100nL处理16~48h，对‘通新斯’和‘Saijo’果实软化的抑制时间分别为12d和16d。从采收到1-MCP处理开始的12h的时间间隔不会损害1-MCP的有益效果。这些结果表明，1-MCP是一种很有前途的延长日本柿货架期的化学品。较少

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