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 I 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 (PpSUSI), AIV (PpAIVI and PpAIV2) and SPS (PpSPSI) during storage. Cold treatment increased expression of PpAIVI, especially after 14 days of storage and resulted in a slight decrease in PpSPSI transcripts. Cold plus 1-MCP inhibited accumulation of PpAIVI and a decrease in PpSPSI. PpAIV2 and PpSUSI expression was largely unaffected by cold treatment. The increase in PPAIVI transcript through cold storage with the concomitant decrease of PpSPSI transcript may lead to an accumulation of hexoses and a decrease of sucrose. (C) 2007 Elsevier B.V. All rights reserved.