Effects of Storage Temperature on Fruit Quality and Expression of Sucrose Phosphate Synthase and Acid Invertase Genes in Japanese Pear

Japanese pear (Pyrus pyrifolia Nakai) ‘Gold Nijisseiki’ fruit were stored for 28 days at 0, 4, 10, 15, or 22°C. The effects of storage temperature on sucrose metabolism and on the expression of genes for sucrose-metabolizing enzymes were investigated. Fruit firmness, skin color, and content of various sugars were affected by storage temperature. Fruit stored at 22°C underwent rapid fruit softening and skin color change. Fruit stored at 15 or 10°C had lower sucrose content and higher glucose and fructose content than those stored at 0, 4, or 22°C. To investigate whether sucrose loss is related to changes in the expression of sucrose-metabolizing enzymes (vacuolar acid invertase: AIV; and sucrose phosphate synthase: SPS), we examined the expression of 3 genes during storage, namely, those encoding AIV (PpAIV1 and PpAIV2) and SPS (PpSPS1). Storage at 10 and 15°C increased the expression of PpAIV2 within a week and that of PpAIV1 in 14 days, while storage at 0 and 4°C delayed increased expression of PpAIV1 and PpAIV2 until after 28 days. Changes in the gene expression of sucrose-metabolizing enzymes were followed by delayed responses in sugar content.