starch, vine, an insoluble carbohydrate polymer composed of glucose residues. It is non-osmotic and is the principal storage substance in plants, forming as starch grains. Starch grains occur in the leaf and in cells of storage tissue in stems and roots of the vine. During daylight hours, when sucrose levels rise in leaves due to photosynthesis, starch grains build up. At night they are metabolized to provide the sugar needed for respiration (this is also their fate in the human gut). Starch, natural storage reserves, are remobilized when buds burst and shoots begin to grow. Unlike many fruits, grape berries do not contain much starch, which is one reason why grapes do not ripen after picking (apart from changes associated with dehydration). Starch is the principal carbohydrate reserve of vines.