title: Mechanisms of water transport mediated by PIP aquaporins and their regulation via phosphorylation events under salinity stress in barley roots.
abstract: Water homeostasis is crucial to the growth and survival of plants under water-related stress. Plasma membrane intrinsic proteins (PIPs) have been shown to be primary channels mediating water uptake in plant cells. Here we report the water transport activity and mechanisms for the regulation of barley (Hordeum vulgare) PIP aquaporins. HvPIP2 but not HvPIP1 channels were found to show robust water transport activity when expressed alone in Xenopus laevis oocytes. However, the co-expression of HvPIP1 with HvPIP2 in oocytes resulted in significant increases in activity compared with the expression of HvPIP2 alone, suggesting the participation of HvPIP1 in water transport together with HvPIP2 presumably through heteromerization. Severe salinity stress (200 mM NaCl) significantly reduced root hydraulic conductivity (Lp(r)) and the accumulation of six of 10 HvPIP mRNAs. However, under relatively mild stress (100 mM NaCl), only a moderate reduction in Lp(r) with no significant difference in HvPIP mRNA levels was observed. Sorbitol-mediated osmotic stress equivalent to 100 and 200 mM NaCl induced nearly identical Lp(r) reductions in barley roots. Furthermore, the water transport activity in intact barley roots was suggested to require phosphorylation that is sensitive to a kinase inhibitor, staurosporine. HvPIP2s also showed water efflux activity in Xenopus oocytes, suggesting a potential ability to mediate water loss from cells under hypertonic conditions. Water transport via HvPIP aquaporins and the significance of reductions of Lp(r) in barley plants during salinity stress are discussed.
authors: Group of Molecular and Functional Plant Biology, Institute of Plant Science and Resources, Okayama University, 20-1 Chuo-2-chome, Kurashiki, Okayama 710-0046, Japan.
authors: Tomoaki
authors: T
authors: Horie
authors: Toshiyuki
authors: T
authors: Kaneko
authors: Genki
authors: G
authors: Sugimoto
authors: Shizuka
authors: S
authors: Sasano
authors: Sanjib Kumar
authors: SK
authors: Panda
authors: Mineo
authors: M
authors: Shibasaka
authors: Maki
authors: M
authors: Katsuhara
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D020346:Aquaporins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D009997:Osmotic Pressure; D010766:Phosphorylation / Q000187:drug effects; D010802:Phylogeny; D010940:Plant Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018520:Plant Shoots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000494:pharmacology*; D013012:Sorbitol / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D014867:Water / Q000378:metabolism*; D014981:Xenopus / Q000235:genetics / Q000378:metabolism
chemical_list: D020346:Aquaporins; D004791:Enzyme Inhibitors; D010940:Plant Proteins; C110065:major intrinsic protein, plant; D014867:Water; D012965:Sodium Chloride; D013012:Sorbitol; D019311:Staurosporine