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

Abstract

Activities of NAD+-dependent sorbitol dehydrogenase (SDH), sucrose synthase (SS), acid invertase (AI), and neutral invertase (NI) in ‘Encore’ peach (Prunus persica L.) fruits and developing shoot tips were followed during the growth season to see whether they could serve as indicators of sink strength. In fruit flesh, SS was active during stage I of growth, when cells were actively dividing, and SDH activity was detected during stage III, when cells were actively enlarging. Acid invertase was active in stage I and showed the best correlation with the relative increase in fruit weight during the season. During seed filling and pit hardening (stage II), when relative fruit growth rate was slowest, activities of carbohydrate metabolizing enzymes in fruit flesh were not detectable. No sorbitol oxidase (SOX) activity was detected during stages I and II. The highest sucrose content occurred when sucrose metabolizing enzyme activities were low, near the end of fruit development. In developing shoot tips, SDH activity was low at the beginning and end of the season when vegetative growth was slowest. Also, shoot tips exhibited a 2 : 1 sorbitol : sucrose (w : w) ratio during these periods. A 1 : 1 sorbitol : sucrose (w : w) ratio along with an increase in SDH activity was present in shoot tips during mid-growing season. In root tips of ‘Nemaguard’ peach, SDH exhibited its highest activity compared to that in other organs. When sorbitol and sucrose metabolizing enzyme activities were correlated with shoot growth of ‘Nemaguard’ plants, only SDH activity showed a positive response.