Vacuolar Compartments

Research into plant vacuoles has, over the last 5 years or so, been injected with new data which has already radically changed our concept of the vacuolar compartment in plant cells. In fact, we should no longer speak of the vacuole, but rather of vacuolar compartments which are functionally different entities and can coexist in the same cell. There is no longer a universal vacuole in which all vacuolar functions can be recognized. Single types of vacuole may be present in a plant cell, but they may give way to other types during development, and a single type of vacuole may arise through fusion of different ones. Vacuoles can be distinguished not only on the basis of their stored contents, but also in terms of the processing of enzymes that they contain and the type of aquaporin present in their boundary membrane, the tonoplast. The multi-vacuole hypothesis, as we might term it, has considerable repercussions for protein trafficking, making the plant cell a considerably more complex system to work with than in other eukaryotes.