The present invention relates to DNA molecules encoding enzymes which are involved in the starch synthesis of plants. These enzymes represent two different isotypes of the soluble starch synthase as well as a starch granule-bound starch synthase. This invention furthermore relates to vectors, bacteria, as well as to plant cells transformed with the DNA molecules described and to plants regenerated from them.Furthermore, the invention relates to starch that can be isolated from plants having an increased or reduced activity of the proteins described.