Starch Hydrolytic Enzyme Activities Following Defoliation of White Clover

White clover (Trifolium repens L.) is an important legume in grass-land ecosystems. Its persistence in mixed grass-clover swards, however, is dependent on utilization of stored carbohydrates during over-wintering and subsequent spring regrowth. Reserve carbohydrate is stored as starch in stolons. Our objective was to determine how activities of starch hydrolytic enzymes change during defoliation-induced starch mobilization in clover stolons. Starch degradation was induced by defoliating clonally propagated plants maintained in a controlled environment. Defoliation resulted in rapid, extensive starch remobilization from older stolon tissues, and prevented starch accumulation in young, developing stolon tissues. Amylase activities of stolon tissue were determined immediately, 1, 2, 4, 8, and 12 d post-defoliation. Total amylolytic activity decreased following defoliation. Of the starch hydrolytic enzyme activities determined, only the activity of α-amylase increased as a consequence of defoliation (two-fold, with respect to the control). β-amylase, which constituted the greatest proportion of total amylolytic activity, decreased two- to three-fold in stolons of defoliated plants, but increased six-fold in young stolon tissue, and almost two-fold in old stolon tissue. The increase in enzyme activity correlated with starch deposition in control plants. Starch phosphorylase activity also decreased as a result of defoliation, while activity of α-glucosidase changed little following the defoliation treatment. Our results suggest starch degradation in stolons of white clover is regulated by α-amylase activity.