J Integr Plant Biol. ›› 2001, Vol. 43 ›› Issue (5): 441-460.

• Research Articles •     Next Articles

Plasmodesmata: Dynamic Channels for Symplastic Transport

MA Fengshan, Carol A. PETERSON   


Plasmodesmata (PDs) are cytoplasmic structures that link adjacent cells to form the symplast of a plant. PDs are involved extensively in a plant's life by mediating symplastic transport of a wide range of ions and molecules. Major components of a plasmodesma (PD) include a plasma membrane, a desmotubule, and a cytoplasmic annulus, all of which are readily detectable by electron microscopy. Both the plasma membrane and the desmotubule contain proteinaceous particles, thought to be involved in altering the size of the cytoplasmic annulus. Cytoskeleton elements (actin and myosin) are essential for maintaining the integrity of PDs. Together with these elements, calcium-binding proteins probably play a significant role in regulating PD function. Symplastic transport occurs through the cytoplasmic annulus for the great majority of solutes, while other substances may traverse through the desmotubule internal compartment, the desmotubule shell, or the plasma membrane. The symplast is subdivided into several domains with varying molecular size exclusion limits (ranging from <1 kD to >10 kD). Plasmodesmata can be either primary or secondary; the former are developed during new wall formation and the latter are made in existing walls. The dynamic nature of plasmodesmata is also reflected by their changing frequencies, which, in turn, depend on the developmental and physiological status of the tissue or the entire plant. While diffusion is the major mechanism of symplastic transport, plasmodesmata are selective for certain ions and molecules. Upon viral infection, viral movement proteins interact with PD receptor proteins and, as a result of yet unknown mechanisms, the plasmodesmata are remarkably dilated to allow viral movement proteins and the bound viral genome to enter healthy cells. Some proteins of plant origin are also able to traverse plasmodesmata, presumably in ways similar to viral movement proteins. Some of these plant proteins are probably signal molecules contributing to cell differentiation and other activities. Other proteins move cell-to-cell in a non-specific manner.

马丰山1,2* Carol A.PETERSON 1

(1. Department of Biology, Unixersity of Waterloo, Waterloo,Ontario N2L 3G1, Canada;2.Department of Biology, Unixersity of  Guelph,Guelph,Ontario N1G2W1,Ganada)


关键词: 细胞骨架;移动蛋白;韧皮部;胞间连丝;蛋白质;可过分子限度;共质体运输;病毒

Key words: cytoskeleton, movement protein, phloem, plasmodesmata, protein, size exclusion limit, symplastic transport, virus

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