Inhibition of sucrose loss during cold storage in Japanese pear (Pyrus pyrifolia Nakai) by 1-MCP

Maintaining fruit taste during storage is important in many fruit species, including Japanese pear. Since sugars are one of the most important components of fruit taste and quality, we examined changes in sugar metabolism during storage in Japanese pear (Pyrus pyrifolia Nakai cvs. Gold Nijisseiki and Hosui). Storage at room temperature (control) resulted in rapid fruit softening and chlorophyll degradation, whereas these processes were delayed by cold storage. Moreover, additional treatment with 1-MCP (1-methylcyclopropene) extended storage periods for another month compared with cold treatment alone. Thus, cold temperature plus 1-MCP treatment is the most effective method for long storage. Total sugar content was maintained during storage in all treatments. However, cold storage led to an accumulation of hexoses and a decrease of sucrose. After 1 month of cold storage, sucrose content was almost zero, but was maintained in control fruit. However, additional treatment with 1-MCP inhibited sucrose loss and accumulation of hexoses. To investigate whether sucrose loss was related to changes in the expression of sucrose metabolizing enzymes (sucrose synthase, SS; soluble acid invertase, AIV and sucrose phosphate synthase, SPS), we examined the expression of four genes, including SS (PpSUS1), AIV (PpAIV1 and PpAIV2) and SPS (PpSPS1) during storage. Cold treatment increased expression of PpAIV1, especially after 14 days of storage and resulted in a slight decrease in PpSPS1 transcripts. Cold plus 1-MCP inhibited accumulation of PpAIV1 and a decrease in PpSPS1. PpAIV2 and PpSUS1 expression was largely unaffected by cold treatment. The increase in PpAIV1 transcript through cold storage with the concomitant decrease of PpSPS1 transcript may lead to an accumulation of hexoses and a decrease of sucrose.