The Sucrose-to-Hexose Ratio is a Significant Determinant for Fruit Maturity and is Modulated by Invertase and Sucrose Re-Synthesis During Fruit Development and Ripening in Asian Pear (Pyrus pyrifolia Nakai) Cultivars
Bok‐Rye Lee, Jeong-Hwa Cho, Seung Gon Wi, Ung Suk Yang, Woo‐Jin Jung, Sang-Hyun Lee
Abstract
This study investigated the regulatory mechanism controlling fruit maturity, focusing on sugar metabolism during pear fruit development and ripening. Three Asian pear cultivars, 'Wonhwang' (early-maturity), 'Whangkeumbae' (early-maturity), and 'Niitaka' (late-maturity), were selected. Absolute growth rate was the highest at 117 days after full bloom (DAFB) in early-maturing cultivars, 'Wonhwang' and 'Whangkeumbae', and at 147 DAFB in the late-maturing cultivar, 'Niitaka'. Hexose (glucose and fructose) content was relatively higher in 'Wonhwang' and 'Whangkeumbae' than in 'Niitaka' during the early stage of fruit development, concomitant with an increase in the activities of cell wall invertase (CWINV), vacuolar invertase (VINV), and neutral invertase (NINV). During the late stage of fruit development, sucrose content and the sucrose-to-hexose ratio were relatively higher in 'Wonhwang' and 'Whangkeumbae' than in 'Niitaka', accompanied by an increase of sucrose phosphate synthase (SPS) activity involved in sucrose re-synthesis. Principal component analysis (PCA) distinctly separated the fruit development into two parts, showing a shift in the early to late stage of fruit development, consistent with the point when the sucrose-to-hexose ratio began to increase. During the late stage of fruit development and ripening, the sucrose-to-hexose ratio was positively correlated with fresh weight, CWINV, and SPS activities and negatively correlated with starch or NINV and VINV activities. These results indicate that the sucrose-to-hexose ratio is an important factor in regulating fruit maturity and is modulated by invertases and SPS activities.