Ripening of 'Red Rosa' plums: effect of ethylene and 1-methylcyclopropene

'Red Rosa', a Japanese type plum, was treated with 0.1 ppm 1-methylcyclopro pene (1-MCP) for 20 h at 20 degreesC at harvest and then held at 20 degrees C for ripening together with untreated fruit, or placed at 0 degreesC stora ge for 5 weeks. Another batch of plums were exposed to 15 ppm ethylene duri ng storage at 0 degreesC. Fruits ripening directly after 1-MCP treatment ha d 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 acti vities were similar in 1-MCP-treated and control fruits. Cell wall enzyme a ctivities 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 r ipening after storage, while the mRNA abundance was highest in control frui t at removal from storage. ACC synthase (ACS) activity was higher in contro l and 1-MCP-treated fruit than in ethylene-treated during ripening after st orage, and message abundance was highest at removal from storage in control fruit. ACC content was highest in fruits at removal from storage. The resu lts are discussed in terms of the role of ethylene in ripening of 'Red Rosa ' plums.