A water stress treatment was imposed on peach trees [Prunus persica (L.) Batsch `Kansuke Hakuto' (Peach Group)] to elucidate the relationship among sugar accumulation, sugar metabolism, and abscisic acid (ABA) in fruit under water stress. Treatment was carried out on peach trees grown in containers from 8 July 1996 [80 days after full bloom (DAFB)] for 16 days, to achieve a predawn water potential of -0.8 to -1.1 MPa compared to that of -0.4 to -0.6 MPa in control trees. Levels of sorbitol, sucrose, and total sugars, as well as the activity of sorbitol oxidase increased in fruit of water stressed trees under moderate water stress (-0.8 MPa), whereas under severe water stress (-1.1 MPa), no difference between the waterstressed trees and the controls was observed. Water stress also induced an increase in ABA in the fruit. These initial results indicated that water-stress-induced ABA accelerated sugar accumulation in peaches by activating sorbitol metabolism.
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