The role of aquaporins in cellular and whole plant water balance

Aquaporins are water channel proteins belonging to the major intrinsic prot ein (MIP) superfamily of membrane proteins. More than 150 MIPs have been id entified in organisms ranging from bacteria to animals and plants. In plant s, aquaporins are present in the plasma membrane and in the vacuolar membra ne where they are abundant constituents. Functional studies of aquaporins h ave hitherto mainly been performed by heterologous expression in Xenopus oo cytes. A main issue is now to understand their role in the plant, where the y are likely to be important both at the cellular and at the whole plant le vel. Plants contain a large number of aquaporin isoforms with distinct cell type- and tissue-specific expression patterns. Some of these are constitut ively expressed, whereas the expression of others is regulated in response to environmental factors, such as drought and salinity. At the protein leve l, regulation of water transport activity by phosphorylation has been repor ted for some aquaporins. (C) 2000 Elsevier Science B.V. All rights reserved .