Horticultural Science and Technology ISSN:1226-8763(Print) 2465-8588(Online) 원예과학기술지

This study aimed to investigate the relationships among fruit size and protein metabolism and profiles during fruit development and ripening of three Asian pear (Pyrus pyrifolia Nakai) cultivars predominantly grown in Korea. The final fruit dry weight was higher in the late-maturing cultivar ‘Niitaka’ than in the early-maturing cultivars ‘Wonhwang’ and ‘Whangkeumbae’. After 87 days after full bloom (DAFB), the fruit amino acid content significantly decreased in ‘Niitaka’ and ‘Wonhwang’ pears, while they remained stable at lower levels in the ‘Whangkeumbae’ pears during fruit development and ripening. At the beginning of our sampling period (57 DAFB) the protein content was the highest in ‘Niitaka’, followed by ‘Wonhwang’ and ‘Whangkeumbae’. The fruit protein content gradually decreased to 117 DAFB for ‘Niitaka’ or 102 DAFB for ‘Wonhang’ and ‘Whangkeumbae’, and then maintained at the similar level to the last sampling date. These reductions in the protein content were consistent with the increases in the protease activity. A rapid increase in the protease activity was observed in the ‘Niitaka’ and ‘Wonhwang’ pears during the early stage of fruit development, whereas a gradual increase was observed in the ‘Whangkeumbae’ pears during the entire period analyzed. The protein pattern varied across the various fruit developmental stages, revealing up- and down-regulated proteins during fruit development as well as highly expressed proteins at the middle phase of the period evaluated. Our results indicate that protein degradation by proteases in the early stage of fruit development, which in turn determines the fruit amino acid content, may affect the final size of Asian pears.