Different Activities of Pectin-degrading Enzymes Affecting the Growth of Asian Pears

Fruit size is determined by the number and size of cells resulting from cell division and expansion, which are correlated with changes in the cell wall content. The pivotal roles of pectin-methylesterase (PME) and polygalacturonase (PG) have been well documented with regard to fruit ripening. Therefore, this study analyzed fruit growth and pectin contents for three consecutive years (from 2019 to 2021) until 180 days after full bloom (DAFB) at 15-day intervals to examine how pectin in the cell wall components affects fruit growth and development. Although there were no differences in the fruit size at harvest for these three years, the absolute fruit growth rate (AGR) peaked most rapidly in 2020, reaching the maximum fruit size earlier compared to the other two years. The pectin content of fruits in 2020, which showed the fastest growth, remained at a low level early in the growing season compared to those in the other years. The change in the pattern of the gradual increase in the PG activity with a decrease in the PME activity resulted in correspondingly different intersecting points over the three years. We found that the intersection of PME and PG activities observed in the order of 2020, 2021, and 2019 was identical to the order when the fruits reached their final weight. Interestingly, this timeline coincided with the point in time when the AGR increased rapidly over these three years. Differences in fruit volume increases, pectin contents, and pectin-degrading enzyme activities observed during fruit growth over three years suggest that the intersection of PME and PG activities is one of the key factors influencing cell expansion activation. Taken together, these results indicate that the intersection of PME and PG activities may affect the pectin content during fruit growth and development, which in turn affects the fruit growth rate in Asian pears.