Division of Biological Sciences, University of Paisley, Paisley PA1 2BE, UK.
Plant Cell Environ. 2009 Dec;32(12):1761-77. doi: 10.1111/j.1365-3040.2009.02033.x. Epub 2009 Aug 14.
It is not known how the uptake and retention of the key osmolyte K(+) in cells are mediated in growing leaf tissue. In the present study on the growing leaf 3 of barley, we have cloned the full-length coding sequence of three genes which encode putative K(+) channels (HvAKT1, HvAKT2, HvKCO1/HvTPK1), and of one gene which encodes a putative K(+) transporter (HvHAK4). The functionality of the gene products of HvAKT1 and HvAKT2 was tested through expression in Xenopus laevis oocytes. Both are inward-rectifying K(+) channels which are inhibited by Cs(+). Function of HvAKT1 in oocytes requires co-expression of a calcineurin-interacting protein kinase (AtCIPK23) and a calcineurin B-like protein (AtCBL9) from Arabidopsis, showing cross-species complementation of function. In planta, HvAKT1 is expressed primarily in roots, but is also expressed in leaf tissue. HvAKT2 is expressed particularly in leaf tissue, and HvHAK4 is expressed particularly in growing leaf tissue. Within leaves, HvAKT1 and HvAKT2 are expressed predominantly in mesophyll. Expression of genes changes little in response to low external K(+) or salinity, despite major changes in K(+) concentrations and osmolality of cells. Possible contributions of HvAKT1, HvAKT2, HvKCO1 and HvHAK4 to regulation of K(+) relations of growing barley leaf cells are discussed.
目前尚不清楚细胞中关键渗透溶质 K(+)的摄取和保留是如何介导的。在本研究中，我们克隆了编码三种假定 K(+)通道（HvAKT1、HvAKT2、HvKCO1/HvTPK1）全长编码序列的基因，以及编码一种假定 K(+)转运体（HvHAK4）的基因。通过在非洲爪蟾卵母细胞中表达，测试了 HvAKT1 和 HvAKT2 基因产物的功能。这两种都是内向整流 K(+)通道，被 Cs(+)抑制。HvAKT1 在卵母细胞中的功能需要共表达拟南芥中的钙调神经磷酸酶相互作用蛋白激酶（AtCIPK23）和钙调神经磷酸酶 B 样蛋白（AtCBL9），表现出功能的种间互补。在体内，HvAKT1 主要在根中表达，但也在叶组织中表达。HvAKT2 特别在叶组织中表达，HvHAK4 特别在生长的叶组织中表达。在叶片中，HvAKT1 和 HvAKT2 主要在叶肉中表达。尽管细胞中的 K(+)浓度和渗透压发生了重大变化，但基因的表达几乎没有因低外部 K(+)或盐度而发生变化。讨论了 HvAKT1、HvAKT2、HvKCO1 和 HvHAK4 对调节生长大麦叶细胞 K(+)关系的可能贡献。
