Water channel required to facilitate the transport of water across cell membrane. Active as heteromers with PIP1-2, but not as homomers. May interact with PIP1-2 to form heteromers. Highly expressed in roots, shoots and developing tassels, and at lower levels in leaves. Expressed in roots with a circadian rhythm showing an increase at the end of the night period, a peak during the first part of the light period and then a decrease. 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.