| Carbon metabolism in potato tubers is highly influenced by the interconversion between sugar and starch. Growing tubers accumulate starch, and postharvest tubers degrade starch. Starch phosphorylase (STP), in vitro, catalyzes a reversible reaction that synthesizes as well as degrades starch. In this study, the role of STP in potatoes was examined. In growing tubers, STP showed a strong activity and had a similar diurnal change pattern to ADP-glucose pyrophosphorylase (AGPase, a key enzyme for starch synthesis), implying that STP plays a positive role in starch accumulation during tuber growth. In cold-stored tubers, a significant correlation between sugar content and the total activities of STP and invertase (a glucose and fructose forming enzyme) was observed, indicating that STP is involved in sugar accumulation. The results suggest that STP plays a mediatory role in sugar-starch interconversion by either synthesizing or degrading starch depending on physiological and environmental conditions. |
