‘Red Rosa’, a Japanese type plum, was treated with 0.1 ppm 1-methylcyclopropene (1-MCP) for 20 h at 20˚C at harvest and then held at 20˚C for ripening together with untreated fruit, or placed at 0˚C storage for 5 weeks. Another batch of plums were exposed to 15 ppm ethylene during storage at 0˚C. Fruits ripening directly after 1-MCP treatment had lower ethylene production and softened more slowly than untreated fruits. Following storage, both the ethylene-treated and 1-MCP-treated fruits were low in ethylene production and softened more slowly than untreated fruits. They also showed lower exo-polygalacturonase (exo-PG) and endo-glucanase (EGase) activities. Respiration rates, pectin esterase (PE) and endo-PG activities were similar in 1-MCP-treated and control fruits. Cell wall enzyme activities were different amongst the treatments, but did not correlate with the differences in fruit softening. 1-Aminocyclopropane–1-carboxylic acid (ACC) oxidase (ACO) activity was highest in ethylene treated fruit during ripening after storage, while the mRNA abundance was highest in control fruit at removal from storage. ACC synthase (ACS) activity was higher in control and 1-MCP-treated fruit than in ethylene-treated during ripening after storage, and message abundance was highest at removal from storage in control fruit. ACC content was highest in fruits at removal from storage. The results are discussed in terms of the role of ethylene in ripening of ‘Red Rosa’ plums.

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