3.A.3.3.7
Plasma membrane H⁺ ATPase, PMA1 or AHA1 of 949 aas ad 10 TMSs in a 2 + 2 + 6 TMS arrangement. Three isoforms, AHA1, 2 & 3, exhibit different kinetic properties (Palmgren and Christensen, 1994). Both the N- and C-termini are directly involved in controlling the pump activity (Ekberg et al., 2010). Methyl jasmonate elicits stomatal closure in many plant species including A. thaliana, and stomatal closure is accompanied by large ion fluxes across the plasma membrane.  These events appear to be mediated by AHA1 (Yan et al. 2015). It is involved in root nutrient uptake, epidermal stomatal opening, phloem sucrose loading and unloading, and hypocotyl cell elongation (Ding et al. 2021). Auxin activates two distinct, antagonistically acting signalling pathways that converge on rapid regulation of apoplastic pH, a causative determinant of growth. Cell surface-based TRANSMEMBRANE KINASE1 (TMK1) interacts with and mediates phosphorylation and activation of plasma membrane H⁺-ATPases for apoplast acidification, while intracellular canonical auxin signalling promotes net cellular H⁺ influx, causing apoplast alkalinization (Li et al. 2021). Hydrogen sulfide improves salt tolerance through persulfidation of PMA1 in Arabidopsis (Ma et al. 2023). H₂S promotes the binding of PMA1 to the transcriptional growth-regulating factor 4 (GRF4) through persulfidation, and then activating PMA, thus improving the salt tolerance of Arabidopsis (Ma et al. 2023).