Abstract:The relation between starch synthases and starch composition in the germinating pinyon ( Pinus edulis Engelm) seedlings was studied. Using the method of 14C-glucose transferred from 14C-ADPG in the assay of starch synthases activity. Starch was extracted with 32% HC1O4, separated on glass fiber with DMSO, and assayed with the sulfuric acid-phenol method. After the emergence of radicle, starch content increased rapidly accompanied with the increase of starch grains in number and size, the increase of both soluble and granulebound starch synthase activity and the change of the pattern of Western-blot. Amylopectin was the major composition in pinyon starch, accounted for 84% of the total starch. The activity of soluble starch synthase was 1.3 times higher than that of the granule-bound starch synthase, corresponding to the ratio of amylopectin to amylose. This result supports the conventional theory that soluble starch synthase is the major enzyme responsive for the synthesis of amylopectin, and also supports that granule-bound starch synthase is functional in the synthesis of amylopectin.