Endocytosis in plants

Endocytosis in animal cells has been heavily documented. Both fluid-phase and receptor-mediated modes of uptake have been frequently studied, and the endocytic pathway is well defined. This contrasts markedly with the situation in plants where our knowledge of this process is still rudimentary. Partly responsible for this situation has been the view, widely held among plant physiologists, that because of turgor, endocytosis cannot occur in plant cells. As discussed below, the case against endocytosis is no longer water-tight.
Endocytosis is a fact in protoplasts. It can be demonstrated with electron-dense tracers as well as with membrane impermeant dye Lucifer Yellow CH. The latter has also been used with success on both suspension-cultured and tissue cells of higher plants, suggesting that fluid-phase endocytosis is also a feature of cells with walls. Through the application of fluorescently labelled elicitor molecules, which specifically bind to the cell surface of suspension-cultured cells, it has also been possible to provide convincing evidence for the operation of receptor-mediated endocytosis in plants. A number of studies on protoplasts and cells clearly indicate that endocytosis in plants can be mediated by coated pits in the plasma membrane. At least one of the organelles that lie on the endocytic pathway in plants has a structurally similar counterpart in animal cells: the multivesicular body. The first recipient of internalized molecules is the partially coated reticulum, although its relationship to the Golgi apparatus and Golgi function remain to be clarified. The final target for endocytosis in plants appears to be the vacuole.