Abstract: Systematic observation of the ultrastructural changes in the fruit mesocarp cells of the "Kyoho' grapevine ( Vitis vinifera × V. labrusca ) with transmission electron microscopy was conducted. The nhrastructure of a mesocarp cell during the developmental phase Ⅰ (the first rapid growth phase) was mainly characterized by the following features: a large central vacuole; a compact cell wall with evenly stained material distributed in the wall, of which the middle lamella was not easily distinguishable; a electron-dense cytoplasm; a full nucleus of often banana-shaped; numerous highly developed mitochondria distributed around the plastids; plentiful tube-like rough endoplasmic reticula; a quantity of vesicles present in the protoplasm, within which many being coalesced and merged into the central vacuole; small vesicles traversed in array through some plasmadesmata; many developed chloroplast or plastids, within some of which were accumulated starch grains. All of these cellular ultrastructural characteristics during the phase Ⅰ suggested the existence of a very active material and energy metabolism. During the developmental phase Ⅱ (lag phase of berry growth), the most marked ultrastructural changes in the mesocarp cells was a nuclear envelope invagination leading to the formation of the lamella or lobed nucleus with a higher electron density in the agglomerate karyoplasm than that in phase Ⅰ , which was considered as an expansion of the interface between nucleus and cytoplasm so to facilitate the communication between them;some organella such as mitochondria and plastids were wrapped in this lamella nucleus as a result of the invagination of cytoplasm to nucleus; the cytoplasm was less electron-dense than in phase I; plenty of the mitochondria appeared to be distributed preferably around the nucleus and vesicles; a'large number of vesicles formed from dilation of the rough endoplasmic reticulum cisterna merged into the central vacuole and occasionally were seen on the brink of plasma membrane; some circled rough endoplasmic reticula enclosed a portion of the cytoplasm, which were thought to result in cytoplasmic autolysis; the tonoplast structure remained intact;the number of plastids decreased and the starch grains found within it during phase Ⅰ disappeared in this phase; the electron-dense middle lamella of cell wall was clearly visible; invagination or exvagination occurred in the wall and plasma membrane of some cells. Based on the main cytological features during the phase Ⅱ , it was deduced that some intense activities of material metabolism and interor intracellular signal communications were being carried on in the mesocarp cells during this stage under the calm or almost unchanged morphological appearance of the fruit, in order to prepare the sudden change of the developmental phase m . During the developmental phase Ⅲ (second rapid growth phase or ripening period), mesocarp cells presented an obvious process of senescence and degeneration: the cell walls lost their integrity or even disappeared in some cells; the cytoplasm .became very thin or almost electron-transparent, in which only some vesicles, a quantity of wadding debris of dissolved cytoplasmic components and some lipid bodies were left; cytoplasmic contents such as vesicles were fused into the central vacuole of which the tonoplast nearly disappeared. Nevertheless the mitochondria remained intact and numerous; and the plasma membranes appeared still in their integrity, which could be related to the maintenance of berry growth or ripening.

Key words: Grapevine fruit, Developmental phase, Mesocarp cell, Ultrastructure