Sugar accumulation in peach fruit as affected by abscisic acid (ABA) treatment in relation to some sugar metabolizing enzymes

Spraying 500 mg . liter(-1) abscisic acid (ABA) on fruit 90 days after full bloom (DAFB) enhanced sugar accumulation in 'Hakuho' peach fruit which was accompanied by a temporal rise in ABA content. Simultaneously, the activit y of sorbitol axidase (SOX), a predominant enzyme in the metabolism of the translocated sugar alcohol, sorbitol, increased. Activities of the sugar me tabolizing enzymes, sucrose synthase (SS), sucrose phosphate synthase (SPS) , and acid invertase were unaffected by the ABA treatment, whereas NAD(+)-d ependent sorbitol dehydrogenase (SDH) activity was not detected. These resu lts indicate that ABA may stimulate SOX activity, enhancing sugar accumulat ion in the fruit. Possible mechanisms of accelerated sugar accumulation by ABA are discussed in relation to sugar metabolism.