Ethylene regulation of sugar metabolism in climacteric and non-climacteric plums

We studied the effect of ethylene regulation on sugar metabolism in fruit of two Japanese plum (Prunus salicina Lindl.) cultivars, the climacteric Santa Rosa and its non-climacteric bud mutant Sweet Miriam, throughout ripening in postharvest storage. These cultivars share the same genetic background but due to bud mutations differ in their ripening behavior. We examined the responses to ethylene (propylene) and 1-methylcyclopropane (1-MCP) treatments on 11 key sugar metabolism-associated genes by integrating gene expression profiling and their associated sugar contents. Our results demonstrated that ethylene was a crucial factor affecting overall sugar metabolism in both ripening types. More specifically, ethylene reduced sucrose catabolism and induced sucrose biosynthesis but inversely, stimulated sorbitol breakdown and decrease sorbitol biosynthesis. Our analyses indicated that glucose and fructose contents result from sorbitol and sucrose breakdown in climacteric and non-climacteric fruit, respectively. In addition, a positive interaction was observed between ethylene and galactose metabolism; while a negative effect of ethylene was reported on galactinol, raffinose, myo-inositol and trehalose, which were higher in non-climacteric Sweet Miriam fruit and could contribute to increased fruit tolerance towards the stress imposed by the ripening process per se and to withstand postharvest storage.