Fruit ripening in response to treatments with propylene, 1-methycyclopropene (1-MCP), and low temperature was characterized in ‘Sanuki Gold’ kiwifruit, Actinidia chinensis Planch. Propylene treatment immediately induced rapid fruit softening, increased AC-PG (polygalacturonase) and AC-EXP (expansin) mRNA accumulation, and stimulated an increase in the soluble solid concentration (SSC) and a decrease in titratable acidity (TA). After 3 d exposure to propylene, ethylene production and AC-PL (pectate lyase) mRNA accumulation were observed. 1-MCP treatment after 24 h exposure to propylene eliminated AC-PG mRNA accumulation and suppressed continued changes in SSC and TA. Application of 1-MCP at the start of the treatment, followed by continuous propylene exposure, markedly delayed fruit softening, and the expression of the cell wall-modifying genes, and changes in the SSC and TA, indicating that kiwifruit become insensitive to ethylene at least for 3 d following 1-MCP exposure. Surprisingly, significant fruit softening, mRNA accumulation of AC-PG, AC-PL, and AC-EXP, and decreased TA were observed without ethylene production in intact fruit stored at low temperature for 1 month, but not in fruit stored at room temperature. Repeated 1-MCP treatments (twice a week) failed to inhibit the changes that occurred in low temperature storage. These observations indicate that low temperature modulates the ripening of kiwifruit in an ethylene-independent manner, suggesting that kiwifruit ripening is inducible by either ethylene or low temperature signals.

The effects of modified atmosphere (MA) storage and application of 1-methylcyclopropene (1-MCP) at harvest on the storability and quality of 'Sanuki Gold' kiwifruit harvested at two different maturity stages were investigated. MA storage in both fruit harvested early at 136 days after pollination (DAP) or late at 154 DAP delayed flesh softening, increase in soluble solid concentrations (SSC), decrease in titratable acids (TA), and reduction in fruit flesh color index compared to air stored fruit, suggesting that MA storage is effective in prolonging 'Sanuki Gold' kiwifruit storage life. Further, MA stored fruit did not attain full ripening flesh firmness and SSC thresholds even after 4 months of storage under MA conditions, suggesting that early harvested 'Sanuki Gold' kiwifruit can be stored for 4 months in MA. Fruit from both harvesting maturity stages stored under air conditions achieved maximum SSC (18%) values during storage, suggesting that two weeks early harvesting did not compromise edible quality characteristics. Only late harvested fruit treated with 1-MCP and stored in MA showed slight inhibitory effect specific to fruit softening during the first and second month of storage, suggesting that 1-MCP may have some limited ripening inhibitory effect during storage of 'Sanuki Gold' kiwifruit.