The Sucrose Analog Palatinose Leads to a Stimulation of Sucrose Degradation and Starch Synthesis When Supplied to Discs of Growing Potato Tubers

Abstract

In the present paper we investigated the effect of the sucrose (Suc) analog palatinose on potato (Solanum tuberosum) tuber metabolism. In freshly cut discs of growing potato tubers, addition of 5 mm palatinose altered the metabolism of exogenously supplied [U-14 C]Suc. There was slight inhibition of the rate of 14 C-Suc uptake, a 1.5-fold increase in the rate at which 14 C-Suc was subsequently metabolized, and a shift in the allocation of the metabolized label in favor of starch synthesis. The sum result of these changes was a 2-fold increase in the absolute rate of starch synthesis. The increased rate of starch synthesis was accompanied by a 3-fold increase in inorganic pyrophosphate, a 2-fold increase in UDP, decreased UTP/UDP, ATP/ADP, and ATP/AMP ratios, and decreased adenylate energy charge, whereas glycolytic and Krebs cycle intermediates were unchanged. In addition, feeding palatinose to potato discs also stimulated the metabolism of exogenous 14 C-glucose in favor of starch synthesis. In vitro studies revealed that palatinose is not metabolized by Suc synthases or invertases within potato tuber extracts. Enzyme kinetics revealed different effects of palatinose on Suc synthase and invertase activities, implicating palatinose as an allosteric effector leading to an inhibition of Suc synthase and (surprisingly) to an activation of invertase in vitro. However, measurement of tissue palatinose levels revealed that these were too low to have significant effects on Suc degrading activities in vivo. These results suggest that supplying palatinose to potato tubers represents a novel way to increase starch synthesis.

Inhibition of de Novo Pyrimidine Synthesis in Growing Potato Tubers Leads to a Compensatory Stimulation of the Pyrimidine Salvage Pathway and a Subsequent Increase in Biosynthetic Performance

“…Tuber discs were extracted with 80% (v/v) ethanol at 808C (1 mL per two discs) and reextracted in two subsequent steps with 50% (v/v) ethanol (1 mL per two discs at each step), the combined supernatants were dried under an air stream at 408C and taken up in 1 mL of water, and label was separated by ion-exchange chromatography and thin layer chromatography as described by Fernie et al (2001a). The insoluble material left after ethanol extraction was analyzed for label in starch, cell wall, and protein as described by Fernie et al (2002).…”

Alterations in Cytosolic Glucose-Phosphate Metabolism Affect Structural Features and Biochemical Properties of Starch-Related Heteroglycans

“…Subsequently, the pellet was rapidly resuspended in water (2 mL) and an aliquot was used to monitor radioactivity by liquid scintillation counting. Hexoses and Suc from the ethanol-soluble fraction and starch, protein, and cell wall matter were separated by enzymatic degradation as described by Carrari et al (2006) and by subsequent anion-exchange chromatography as detailed by Fernie et al (2001).…”

Manipulation of Photosynthesis in Grape (Vitis vinifera) CV. ‘Flame’ by the Application of Two Sucrose Analogs

“…By other side, 5 mM concentrations of the sucrose analogs palatinose and turanose had been shown to trigger the same kind of metabolic responses as sucrose (Fernie et al, 2001). However, they cannot be metabolized by the plant (Loreti et al, 2000) and they cannot be translocated as the normal sucrose (Bornke et al, 2002).…”