The sucrose analog palatinose leads to a stimulation of sucrose degradation and starch synthesis when supplied to discs of growing potato tubers

dIn the present paper we investigated the effect of the sucrose (Suc) analo g palatinose on potato (Solanum tuberosum) tuber metabolism. In freshly cut discs of growing potato tubers, addition of 5 mM palatinose altered the me tabolism of exogenously supplied [(UC)-C-14]Suc. There was slight inhibitio n of the rate of C-14-Suc uptake, a 1.5-fold increase in the rate at which C-14 Suc was subsequently metabolized, and a shift in the allocation of the metabolized label in favor of starch synthesis. The sum result of these ch anges was a 2-fold increase in the absolute rate of starch synthesis. The i ncreased rate of starch synthesis was accompanied by a 3-fold increase in i norganic pyrophosphate, a 2-fold increase in UDP, decreased UTP/UDP, ATP/AD P, and ATP/AMP ratios, and decreased adenylate energy charge, whereas glyco lytic and Krebs cycle intermediates were unchanged. In addition, feeding pa latinose to potato discs also stimulated the metabolism of exogenous C-14-g lucose in favor of starch synthesis. In vitro studies revealed that palatin ose is not metabolized by Suc synthases or invertases within potato tuber e xtracts. Enzyme kinetics revealed different effects of palatinose on Suc sy nthase and invertase activities, implicating palatinose as an allosteric ef fector leading to an inhibition of Suc synthase and (surprisingly) to an ac tivation of invertase in vitro. However, measurement of tissue palatinose l evels revealed that these were too low to have significant effects on Suc d egrading activities in vivo. These results suggest that supplying palatinos e to potato tubers represents a novel way to increase starch synthesis.