1.A.8.11.3
Plasma membrane aquaporin 1, PIP1, PIP1;2, PIP1b, of 286 aas and 6 TMSs (Törnroth-Horsefield et al., 2006).  Transports H₂O, H₂O₂ (Dynowski et al., 2008), O₂ and CO₂ (Zwiazek et al. 2017)_.  Forms active heterotetramers with PIP2;1 (1.A.8.11.4); down regulated under drought stress (Najafabadi et al., 2008); plays a role in salt tolerance (Li et al. 2018). Gated by H⁺, Ca²⁺, Mn²⁺ and Cd²⁺ (Verdoucq et al., 2008). The wheat orthologue has been described (Ayadi et al., 2011). 96% identical to PIP1;3. In Selaginella moellendorffii (Sm; spikemoss), SmPIP1;1 is retained in the ER while SmPIP2;1 is found in the plasma membrane but, upon co-expression, both isoforms are found in the plasma membrane as a heterotetramer, leading to a synergistic effect on water membrane permeability (Bienert et al. 2018). In some speices, PIP1 is inactive (e.g., in maize), but formation of a hetrotetramer with PIP2 allows transport (Vajpai et al. 2018). Transmembrane helices 2 and 3 determine the localization of plasma membrane PIPs (Wang et al. 2019). PIP1;2 from Malus domestica confers salt tolerance in transgenic Arabidopsis (Wang et al. 2022).