The morphological examination of starch grains and the quantitative analysis of starch grain size unequivocally demonstrate that antisense tubers contain starch grains with much smaller diameter and more grains per cell. However, the amount of starch is not the only parameter that seems to control the grain size. A Chlamydomonas mutant lacking granule-bound starch synthase activity and no change in total starch content also has smaller grains, which is most likely due to the total absence of amylase.