Abstract
In our previous paper, it was reported that mume fruits became chilling-insensitive when they were harvested at a late period, and that the surface color of the stone may be a useful criterion of harvest time. This paper deals with the changes in stone color, K+ leakage rate, and phospholipid composition with reference to fruit maturity and chilling sensitivity.1. ‘Ohshuku’ mume fruits were harvested at weekly intervals from May 16 to June 13 and investigated for the relation between surface color of the stone and fruit maturity. The stone was white in fruits harvested before May 30, and the embryos were not yet matured. Stone color changed to light brown in fruits harvested on June 6 and the embryos were mature.2. HCl-soluble pectin content decreased rapidly after June 6 and water-soluble pectin content increased concomitantly. Citric acid content increased and malic acid content decreased during maturation; especially, a marked decrease of malic acid content was found after June 6.3. The number of days from harvest to the beginning of rapid increase of CO2 and C2H4 production, and peel yellowing, decreased during maturation. A marked decrease was found between May 23 and June 6.4. As an index of membrane permeability, the rate of K+ leakage was measured at 3, 6, 8°C on the harvest day, and its relation to chilling sensitivity was investigated. The rate of K+ leakage was low in fruits harvested from May 23 to June 6; these fruits showed high chilling sensitivity.5. As an index of membrane flexibility, the phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio was investigated in relation to harvest maturity. Theratio was very low in fruits harvested from May 23 to June 6, which showed high chilling sensitivity. Fruits harvested on June 13 showed a high ratio and low chilling sensitivity.From these results it was concluded that the time of stone-color change from white to light brown or brown coincides with a physiological turning point of fruits, and that mume fruits acquire chilling resistance after that.
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