Role of abscisic acid (ABA) during persimmon maturation and in detached young fruits

Abstract

The changes in endogenous abscisic acid (ABA) content during ‘Hanagosho’ persimmon (Diospyros kaki Thunb.) development and maturation, as well as the effects of ABA, nordihydroguaiaretic acid (NDGA), 1-methylcyclopropene (1-MCP) application and polyethylene film package treatment on detached young fruit during fruit softening and senescence were investigated. The results showed that the ABA content in both peel and pulp peaked at 30 and 140 days after full bloom (DAFB). Moreover, the ABA content in peel at 30 and 140 DAFB was 17 and 29 times higher than in pulp, respectively. Dehydration in detached fruits induced the production of ABA and ethylene, which further led to fruit softening, and during this process ABA peaked earlier than ethylene. Expressions of the ethylene biosynthesis gene DkACS2 and ethylene oxidase gene DkACO1 were increased by the ABA treatment and their expression peaks also appeared earlier. However, expressions of DkACS2 and DkACO1 were down-regulated by the application of NDGA and 1-MCP, and their expression peaks were delayed. The peak time of 9-cis-epoxycarotenoid dioxygenase genes (DkNCED1) expression was not advanced under ABA, NDGA and 1-MCP treatments. In package-treated fruits, expressions of DkNCED1, DkACS2 and DkACO1 were significantly down-regulated and their expression peaks were delayed. In conclusion, we propose that dehydration could induce the expression of DkNCED1 and trigger ABA biosynthesis, while ABA could induce the expressions of DkACS2 and DkACO1, which initiates the biosynthesis of ethylene, consequently accelerating fruit softening and ripening.