Soluble Sugar Concentrations Associated with Tuber and Winter Bud Sprouting

Many aquatic weeds rely on vegetative structures for survival and propagation, rather than seeds. American pondweed ( Potamogeton nodosus Poiret) winter buds , and hydrilla ( Hydrilla verticillata (L.f.) Royle, monoecious and dioecious types) tubers were allowed to sprout in water in the dark. At two-tothree day intervals individual propagules and dependent shoots were analyzed for soluble sugars. There was a significant decline in propagule fresh weight over time indicating mobilization of stored materials. Sucrose was the most abundant soluble sugar in all the propagules, but found in higher concentrations in American pondweed winter buds than in hydrilla propagules. Fructose, glucose, raffinose, and sucrose were present in American pondweed, and hydrilla. Stachyose was present in all except dioecious hydrilla and sorbitol was not detected. During sprouting, soluble sugar concentrations decreased within the original propagule and increased in shoots for hydrilla biotypes. Fructose and glucose concentrations were greater in newly formed shoots than in winter buds of American pondweed by day 14 and in hydrilla shoots versus propagules by day 22. The striking increases in concentrations of these soluble sugars in propagules and newly emergent leaf tissue suggest that starch hydrolysis is a key metabolic control point during sprouting.