Water channel required to facilitate the transport of water across cell membrane. Active as heteromers with PIP1-1, PIP2-1, PIP2-4 or PIP2-5, but not as homomers. Interacts with PIP2-1 to form heteromers. Highly expressed in developing tassels and at lower levels in roots, shoots, ears and embryos. Expressed in the root growing zone at 5-6 mm from the root tip. Expressed in xylem parenchyma. 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. PIP (TC 1.A.8.11) subfamily.