Starch is insoluble in water, yet it is accumulated in large quantities in potato tuber because

Sugars are synthesized in leaves and stored in other parts like seed, root, stem. In a potato, sugars are synthesized in leaves and then transported to stem for storage. Sugars are usually synthesized in hexose form but translocated as sucrose and stored as starch in roots, stems or seeds. Starch is a complex insoluble polysaccharide carbohydrate of green plants, one of the principal energy (food) reserve materials. It is formed by polymerization of several hundred glucose subunits. Though it is insoluble in water, yet it is stored in colourless plastids (leucoplasts) in storage tissues (eg; Potato tuber). It is formed into grains, laid down in a series of concentric layers.