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.
Plant Cell Physiol. 2011 Apr;52(4):663-75. doi: 10.1093/pcp/pcr027. Epub 2011 Mar 24.
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.
水稳态对于植物在与水相关的胁迫下的生长和存活至关重要。已表明质膜内在蛋白（PIPs）是介导植物细胞水分吸收的主要通道。本文报道了大麦（Hordeum vulgare）PIP 水通道蛋白的水运输活性和调节机制。单独在非洲爪蟾卵母细胞中表达时，发现 HvPIP2 而不是 HvPIP1 通道表现出强大的水运输活性。然而，在卵母细胞中共表达 HvPIP1 和 HvPIP2 会导致与单独表达 HvPIP2 相比，活性显著增加，这表明 HvPIP1 通过异源二聚体参与水运输，可能与 HvPIP2 一起。严重盐胁迫（200 mM NaCl）显著降低根水力传导性（Lp(r)）和 10 个 HvPIP mRNAs 中的 6 个的积累。然而，在相对温和的胁迫（100 mM NaCl）下，仅观察到 Lp(r) 适度降低，而 HvPIP mRNA 水平没有显著差异。相当于 100 和 200 mM NaCl 的山梨醇介导的渗透胁迫几乎相同程度地降低了大麦根的 Lp(r)。此外，完整大麦根中的水运输活性据推测需要磷酸化，该磷酸化对激酶抑制剂，星形孢菌素敏感。HvPIP2 也在非洲爪蟾卵母细胞中显示出水流出活性，这表明在高渗条件下，它可能具有介导细胞失水的能力。本文讨论了 HvPIP 水通道蛋白介导的水运输以及在盐胁迫期间大麦植物中 Lp(r) 降低的重要性。
