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

植物水通道蛋白（水通道）以多种亚型存在，并且分布在质膜和液泡膜中。以萝卜的8种同工型（质膜型：PAQ 1a、1b、1c、2a、2b和2c ;液泡型：γ-VM 23和δ-VM 23）为材料，研究了基因表达的生长期特异性和细胞特异性，以及膜上水孔蛋白含量与膜透性的关系。(1)水通道蛋白在萝卜几个组织中的mRNA水平的调查表明，所有的mRNA在下胚轴和生长的主根显着积累。水通道蛋白在幼苗根和下胚轴的中央柱体中高度积累，在叶柄的维管组织中含量丰富。(2)用停流分光光度计测定质膜和液泡膜的渗透水渗透率。萝卜和风车草属CAM植物液泡膜的透水性高于质膜。还 ...更多信息 风车草属植物的两种膜的透性均极低，萝卜属植物的两种膜的透性均极低。这一结果与细胞膜上水通道蛋白的水平一致。(3)在萝卜水通道蛋白的八种亚型中，PAQ 2组成员的mRNA和蛋白质水平在盐和植物激素处理后发生了变化。此外，PAQ 2-组成员的蛋白水平随生长阶段和组织而变化。(4)我们开发了一种新的方法，从植物组织中特异性地分离感兴趣的原生质体，并测定原生质体的透水性。我们检测到萝卜皮层和内皮层原生质体的高透水性（300 μ msec ^<-1>）。(5)通过在酵母中的功能表达和膜制备的停流色谱测定来确定各个亚型的水通道活性。PAQ 1组成员未显示活性。提示该类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