of normal cytosolic osmolarity, aquaporins can play a major role in extension growth by allowing an influx of water into expanding cells - a process necessary to sustain plant development. Plant aquaporins are also important for mineral nutrition and ion detoxification which are both essential for the homeostasis of boron, silicon, arsenic and bicarbonate. Aquaporins in plants are separated into five main homologous subfamilies, or groups: Plasma membrane Intrinsic Protein (PIP) Tonoplast Intrinsic Protein (TIP) Nodulin-26 like Intrinsic Protein (NIP) Small basic Intrinsic Protein (SIP) X Intrinsic Protein (XIP) These five subfamilies have later been divided into smaller evolutionary subgroups based on their DNA sequence. PIPs cluster into two subgroups, PIP1 and PIP2, whilst TIPs cluster into 5 subgroups, TIP1, TIP2, TIP3, TIP4 and TIP5. Each subgroup is again split up into isoforms e.g. PIP1;1, PIP1;2. As isoforms nomenclature are historically based on functional parameters rather than evolutive ones, several novel propositions on plant aquaporines have been arisen with the study of the evolutionary relationships between the different aquaporins. Within the various selection of aquaporin isoforms in plants, there are also unique patterns of cell- and tissue-specific expression. When plant aquaporins are silenced, the hydraulic conductance and photosynthesis of the leaf decrease. When gating of plant aquaporins occurs, it stops the flow of water through the pore of the protein. This may happen for a number of reasons, for example when the plant contains low amounts of cellular water due to drought. The gating of an aquaporin is carried out by an interaction between a gating mechanism and the aquaporin, which causes a 3D change in the protein so that it blocks the pore and, thus, disallows the flow of water through the pore. In plants, there are at least two forms of aquaporin gating: gating by the dephosphorylation of certain serine residues, in response to drought, and the protonation of specific histidine residues, in response to flooding. The phosphorylation of an aquaporin is involved in the opening and closing of petals in response to temperature. In archaea, eubacteria and fungi Certain bacteria and many other organisms also express aquaporins. Aquaporins also been discovered in the fungi- Saccharomyces cerevisiae (yeast), Dictyostelium, Candida and Ustilago and the protozoans- Trypanosoma and Plasmodium. Clinical significance There have been two clear examples of diseases identified as resulting from mutations in aquaporins: Mutations in the aquaporin-2 gene cause hereditary nephrogenic diabetes insipidus in humans. Mice