Abstract: Ultrastructural differentiation of the shoot apex of growing vegetative buds of Torreya grandis was studied. At ultrastructural level, the shoot apex had the same zonation as in microstructure. The main characteristics of zonal differences were: the thickness of the cell walls, the size and the structure of the plastids, and the volume of the vacuoles. In the apical initials, the walls between apical initials and subapical group cells were thick, the vacuoles were distributed mainly in the outer half of the cells, and there were small starch grains in plastids. The walls of the subapical group cells were thick, the vacuoles were large, and the plastids contain large starch grains. In peripheral cells, normally there were no starch grains in plastids, the vacuoles were smaller. But there were numerous plasmodesmata in the cell wall. In the rib meristem, the cells were occupied mainly by large vacuoles and rich starch containing-plastids. Numerous plasmodesmata were in the thicken walls. During the four periods of the seasonal activities, the ultrastructure of tile apical cells also changed. In resting period, in comparison with other periods, starch-plastids were nacre developed, cell walls were thicker, and the vacuoles were larger. In bud expansion period, S-plastids decreased or even disappearedin bud scale formation period, large amount of small vacuoles appeared. In new bud formation period, the size of the vacuoles increases, and many cup-shape plastids appear. The relationships between the activities of the cells and the shape of the nucleus were also studied.

Key words: Torreya grandis, Shoot apex, Ultrastructure