The Arabidopsis thaliana stomatal complex contains a pair of guard cells surrounded by subsidiary cells, which assist in turgor-driven stomatal movement and receive water and ions. This transport, driven by environmental signals, involves a translocation factor of the plasma membrane proton pump H + -ATPase AHA1, PATROL1. In this study, we investigated the responses of PATROL1 to salinity and hyperosmotic stresses. Specifically, we analyzed the effects of 125 mM NaCl or 231 mM mannitol on the

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... tyledon pavement cell cortexes in transgenic A. thaliana seedlings expressing green fluorescent protein (GFP)-tagged PATROL1. Cells treated with NaCl had few GFP-PATROL1-labeled dot-like structures but contained unusual labeled large bodies and rod-like structures. Cells treated with mannitol had similar large bodies, but not rods, indicating that the rod-like structures form specifically under salinity stress conditions. Dual observations of GFP-PATROL1 and red fluorescent protein (RFP)-tagged AHA1 in stress-treated cells revealed that the latter did not accumulate in the stressinduced GFP-PATROL1 structures, suggesting that the stress-induced GFP-PATROL1 structures are not involved in RFP-AHA1 localization. Additionally, the primary root growth of the patrol1 mutant was more sensitive to NaCl treatment than was that of wild type. Thus, PATROL1 appears to contribute to salinity stress tolerance, possibly by regulating membrane trafficking.