Molecular diversities and structural construction, and intrecellular localization of plant aquqporins

植物水通道蛋白（水通道）有多种亚型，分布在血浆和液泡膜中。针对萝卜的8种异构体（质膜型：PAQ1a、1b、1c、2a、2b和2c；液泡型：γ-VM23和δ-VM23），研究了基因表达的生长阶段特异性和细胞特异性，以及膜中水通道蛋白含量与其膜透水性的关系。(1)对萝卜几种组织水通道蛋白mRNA水平的研究表明，所有mRNA在下胚轴和生长的主根中都有显著的积累。水通道蛋白在幼苗根中柱和下胚轴中大量积累，在叶柄维管组织中丰富。(2)用停流分光光度计测定血浆膜和液泡膜的渗透透水性。液泡膜的透水性高于萝卜和葡萄的质膜。此外，葡萄葡萄两种膜的透性均极低于萝卜膜。结果与膜中水通道蛋白的水平一致。(3)在萝卜水通道蛋白的8个同工异构体中，PAQ2组成员的mRNA和蛋白水平随盐和植物激素的处理而发生变化。此外，paq2组成员的蛋白水平随生长阶段和组织而变化。(4)我们开发了一种从植物组织中特异性分离原生质体并测定原生质体透水性的新方法。我们检测到萝卜皮层和内胚层原生质体具有较高的透水性（300 μm sec^<-1>）。(5)通过酵母的功能表达和膜制备的停流分光光度法测定各异构体的水通道活性。PAQ1组成员没有表现出这种活性。提示该型水通道蛋白的其他生化功能。少

Plant aquaporins (water channels) occur in multiple isoforms and are distributed in both plasma and vacuolar membranes. For eight isoforms (plasma-membrane type : PAQ1a, 1b, 1c, 2a, 2b, and 2c ; vacuolar type : γ-VM23 and δ-VM23) of radish, we investigated growth stage specificity and cell-specificity of gene expression and the relationship between the aquaporin content in the membrane and their membrane water permeability.(1) Investigation of mRNA levels of aquaporins in several tissues of radish showed a marked accumulation of all the mRNAs in hypocotyls and growing taproots. Aquaporin proteins were highly accumulated in the central cylinder of seedling root and hypocotyl, and rich in the vascular tissue of the petiole.(2) Osmotic water permeabilities of the plasma and vacuolar membranes were determined with a stopped-flow spectrophotometer. The water permeability of the vacuolar membrane was higher than that of the plasma membrane of radish and Graptopetalum, a CAM plant. Also, the … More permeability of both membranes of Graptopetalum was extremely lower than that of radish membranes. The result is consistent with the level of aquaporin in the membrane.(3) Among eight isoforms of radish aquaporin, the levels of mRNA and protein of members of the PAQ2 group were changed in response to treatment with salt and phytohormones. Furthermore, the protein levels of the PAQ2-group members varied with the growth stage and the tissues.(4) We developed a new method to specifically isolate a protoplast of interest from plant tissues and to determine the water permeability of the protoplast. We detected a high water permeability (300 μm sec^<-1>) of protoplasts from the cortex and endodermis of radish.(5) The water channel activity of individual isoforms was determined by functional expression in yeast and stopped-flow spectrophotometrical assay of the membrane preparation. PAQ1 group members did not show the activity. It suggests the other biochemical function of this type aquaporin. Less