Carbohydrate metabolism of vegetative and reproductive sinks in the late-maturing peach cultivar 'Encore'

Activities of NAD(+)-dependent sorbitol dehydrogenase (SDI-I), sorbitol oxi dase (SOX), sucrose synthase (SS), acid invertase (AI), and neutral inverta se (NI) in 'Encore' peach (Prunus persica L.) fruits and developing shoot t ips were assayed during the growing season to determine whether carbohydrat e metabolizing enzymes could serve as indicators of sink strength. In fruit flesh, SS activity was detected during Stage I of growth, when cells were actively dividing, and SDH activity was detected during Stage III, when cel ls were actively enlarging. Acid invertase activity was detected during Sta ge I and showed a closer correlation with relative increase in fruit weight during the growing season than SS activity. During seed filling and pit ha rdening (Stage II), when relative fruit growth rate was slowest, activities of carbohydrate metabolizing enzymes in fruit flesh were not detectable. N o SOX activity was detected during Stages I and II. The highest sucrose con tent occurred near the end of fruit development when the activities of sucr ose metabolizing enzymes were low. In developing shoot tips, the sorbitol:s ucrose ratio was 2:1 (w/w) and SDH activity was low at the beginning and en d of the season when vegetative growth was slowest. The sorbitol:sucrose ra tio changed to 1:1 (w/w) along with an increase in SDH activity in shoot ti ps during the mid-growing season. In 'Nemaguard' peach, SDH exhibited highe r activity in root tips than in other organs. Among the sorbitol- and sucro se-metabolizing enzyme activities, only SDH activity was positively correla ted with shoot growth in 'Nemaguard' plants.