Cytokinesis in higher plants results in the incomplete separation of daughter cells, due to the formation of special plasma-membrane-lined cytoplasmic bridges, called plasmodesmata. Within the green algae, these structures coordinate biochemical and physiological processes by facilitating the cell-to-cell diffusion of simple metabolites and ions. Until recently, most plant biologists thought that plasmodesmata perform a similar function in higher plants. However, it is now known that the more structurally advanced plasmodesmata of higher plants can also traffic macromolecules, including proteins and nucleic acids. These findings give new insights into how green plants evolved the ability to orchestrate their developmental and physiological processes in a supracellular rather than a multicellular manner.
Bibliographical noteFunding Information:
We thank Don Fisher for providing data on wheat phloem sap, and Mitsuo Chino for detailed infor- mation on rice phloem proteins. Work from our lab oratories was sup ported by National Science Foundation grant No. DCB-90- 16756 (W. J. L.) and United States-Israel Binational Science Foundation grant No. 90-00070 (S. W. and W. I. L.).