Water channel required to facilitate the transport of water across cell membrane. May support the rapid influx of water into vacuoles during cell expansion, permit osmotic equilibration between the cytosol and the vacuolar content and rapid transcellular water flow through living cells. Its function is impaired by Hg(2+). Tonoplast. Expressed in roots, shoots, leaves, tassels, ears and embryos. Expressed in meristems and zones of cell enlargement: tips of primary and lateral roots, leaf primordia, and male and female inflorescence meristems. Highly expressed in the root epidermis and endodermis, parenchyma cells surrounding mature xylem vessels in the root and the stem, phloem companion cells and a ring of cells around the phloem strand in the stem and the leaf sheath, and the basal endosperm transfer cells in developing kernels. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Belongs to the MIP/aquaporin (TC 1.A.8) family. TIP (TC 1.A.8.10) subfamily.