Changes in Prooxidant and Antioxidant Enzymes and Reduction of Chilling Injury Symptoms during Low-temperature Storage of ‘Fuyu’ Persimmon Treated with 1-Methylcyclopropene

‘Fuyu’ perisimmon fruit were treated with 500 nL L 1-methylcyclopropene (1-MCP) for 24 h at 20 8C and then stored at 4 8C for 45 days to investigate the effects of 1-MCP on chilling injury (CI) during storage at 4 8C. Persimmon fruit developed CI, manifested as rapid softening and external and internal browning. Injury symptoms were reduced by 1-MCP treatment. 1-MCP also delayed increases in respiration and ethylene production. Compared with control fruit, 1-MCP-treated fruit exhibited increased superoxide dismutase and catalase activities within the initial storage period and lower membrane permeability, malondialdehyde content, and peroxidase and polyphenol oxidase activities throughout the entire storage period. These results suggest that reduction of CI symptoms in persimmon fruit in response to 1-MCP treatment may be attributed to altered oxidative status. Persimmon (Diospyros kaki L. cv. Fuyu) is a crop of high economic importance in northwest China. The fruit is susceptible to chilling injury (CI) during postharvest storage, developing symptoms at 0 to 4 C that increase in severity with longer storage (Woolf et al., 1997). The symptoms become most severe after transferring fruit to ambient temperature, rendering the fruit unmarketable (Collins and Tisdell, 1995; MacRea, 1987; Sargent et al., 1993). CI in persimmon fruit is expressed as enhanced softening, browning of skin and flesh, flesh gelling, and loss of flavor (MacRea, 1987). There are several physiological changes occur in parallel with CI in persimmon. For example, MacRea (1987) demonstrated that ethylene production and respiration rates increased rapidly along with appearance of CI symptoms after transfer from low temperature to ambient conditions. Beede (1983) noted that CI was enhanced in persimmon fruit by exposure of fruit to 1 mL L or higher ethylene at 20 C before cold storage at 5 to 7 C. These findings indicate that ethylene contributes to the symptomatology of CI in persimmon (Park and Lee, 2005). Other researchers have proposed that development of specific CI symptoms might result from imbalances in cellular oxidative metabolism involving oxidative enzymes, including peroxidase (POD) and polyphenol oxidase (PPO) (Hershkovitz et al., 2005). Oxidative stress could also be promoted by the presence of excess reactive oxygen species (ROS) that induce peroxidation and breakdown of unsaturated fatty acids in membrane lipids (Sevillano et al., 2009). A role for disturbances in redox homeostasis in development of CI in persimmon is indirectly supported by the report of Lee et al. (1993), in which antioxidant (diphenylamine) treatment reduced the incidence of skin browning and inhibited softening in ‘Fuyu’ persimmon fruit during storage at 0 C. 1-Methylcyclopropene (1-MCP), a potent inhibitor of ethylene action (Sisler, 2006), can maintain quality by suppressing ripening and senescence in a wide range of horticultural crops (Blankenship and Dole, 2003; Huber, 2008; Watkins, 2008). 1-MCP has been reported to reduce CI symptoms of coldstored ‘Fuyu’ (Girardi et al., 2003; Kim and Lee, 2005; Krammes et al., 2006) and ‘Rojo Brillante’ (Pérez-Munuera et al., 2009; Salvador et al., 2004) persimmon accompanying with delay of softening. Delay of softening during storage at ambient temperature (20 C) in persimmon treated with 1-MCP has been correlated with inhibition of cell wall-degrading enzymes (Luo, 2004; Xu et al., 2004). Ultrastructural analysis indicated that reduction of CI in 1-MCP-treated ‘Rojo Brillante’ persimmon was associated with maintenance of cell wall integrity and intercellular adhesion (Pérez-Munuera et al., 2009). Although it is clear that some CI symptoms are alleviated by suppression of ethylene action, to our knowledge, there have been no attempts at addressing whether the amelioration of CI symptoms through suppression of ethylene action is accompanied by parallel changes in the oxidative metabolism of persimmon. The objective of this study was to determine whether prestorage 1-MCP application could enhance tolerance to CI in ‘Fuyu’ sweet persimmon fruit during low-temperature storage (4 C). The study specifically addressed the effects of inhibition of ethylene action on changes in the oxidant and antioxidant system, including membrane permeability, membrane lipid peroxidation, and activities of prooxidant (POD and PPO) and antioxidant enzymes [superoxide dismutase (SOD) and catalase (CAT)]. Material and Methods Plant material. Sweet persimmon fruit (Diospyros kaki L. cv. Fuyu) with 70% of surface yellow coloration (ripening initiated) were obtained from a persimmon orchard in Yangling, Shaanxi province on the day of harvest and transported to the postharvest facilities in Northwest A&F University within 12 h. Fruit of uniform size without mechanical damage were selected for the experiments. 1-Methylcyclopropene treatment. ‘Fuyu’ Persimmon fruit were divided into two groups, 300 fruit per group. The two groups were separately placed in two 360-L chambers and one chamber exposed to gaseous 1-MCP (500 nL L) for 24 h at 20 C. The second group of persimmon without exposure to 1-MCP was regarded as the control. 1-MCP gas was released from a commercial powdered formulation (Rohm and Haas Inc., China, a.i. 0.14%). 1-MCP powder (0.29 g) was placed in a 25-mL flask with septa followed by injecting 5 mL KOH (2%). The sealed flask containing 1-MCP was transferred into the 360-L chamber and opened before immediately sealing the chamber. After24 h, the chambers were opened and the fruit transferred to Received for publication 23 July 2010. Accepted for publication 18 Aug. 2010. Zhengke Zhang and Yu Zhang contributed equally to this work. This research was supported by the National Natural Science Foundation of China (30771756). To whom reprint requests should be addressed; e-mail [email protected]. HORTSCIENCE VOL. 45(11) NOVEMBER 201