Symplastic isolation and symplastic continuity are related to a process of cell-to-cell commu- nication via plasmodesmata. Functional states of plasmodesmata are dynamically changing. Opened plasmodesmata facilitate symplastic transport between cells. Closed plasmodesmata isolate a cell or a group of cells and assure their functional integrity. Cell-to-cell communication may also be regulated due to formation of new plasmodesmata and elimination of existing ones. Symplastic continuity is present between mature cells, which perform the same functions, as well as between cells of undiffe- rentiated structures and organs. The cells performing different functions or beginning a differentiation are symplastically isolated. The phenomenon of symplastic isolation is universal in plant organisms. It has been detected in meristematic tissues and in fully differentiated structures. Symplastic continuity, which makes intercellular communication possible and symplastic isolation, which separates particular groups of cells, both regulate processes of growth and development and guarantee proper functioning of cells in mature plant structures.