植物蔗糖运输途径关键节点细胞质膜pH梯度与蔗糖的运输和分配

Sucrose is a very pivotal photosynthate in plants, whose translocation and partitioning is close related to the yield of economic organs in crop plants. In the apoplastic path of sucrose translocation, sucrose is mediated by sucrose transport proteins to cross the plasma membrane and is regulated by transmembrane pH gradients. However, several problems remain to be elucidated. For examples, at the source end, the plasma membranes of sucrose cells export sucrose, while the plasma membranes of sieve-companion cell complexes import sucrose; at the sink end, the plasma membranes of sieve-companion cell complexes exclude sucrose, while the plasma membranes of sink cells absorb sucrose. Therefore the problems need to answer are: is the transmembrane pH gradient related to the direction of sucrose transport by plasma membrane? If so, how does the transmembrane pH gradient affect the function of sucrose transport by plasma membrane? One possibility is that the effect of the transmembrane pH gradient on the sucrose transport function by plasma membrane depends on the value of transmembrane pH gradient. The confocal microscope technique to measure pH distribution in tissues make it possible to approach these problem. In this study, we use arabidopsis as materials and measure the transmembrane pH gradients at the key points along the sucrose translocation path by the confocal microscope, in order to establish the basis of studying the relationship between the transmembrane pH gradients and the sucrose transport function.

蔗糖是重要的光合产物，其运输和分配与产量密切相关。在蔗糖质外体运输途径中，蔗糖跨质膜转运由转运蛋白介导，并受质膜pH梯度调节。然而尚有诸多不明确的问题。例如，在源端，源细胞质膜输出蔗糖，筛管-伴胞复合体质膜输入蔗糖；在库端，筛管-伴胞复合体质膜输出蔗糖，库细胞质膜输入蔗糖，但所有这些细胞质膜pH梯度都是内高外低。所以需要回答的问题是：质膜蔗糖转运方向与质膜pH梯度有关吗？如果是，pH梯度是如何调节不同类型细胞质膜蔗糖转运的？有一种可能是质膜pH梯度的调节作用与梯度的大小有关，而不同蔗糖运输节点细胞的质膜pH梯度存在差异。激光共聚焦显微镜测定pH技术的应用为研究这个问题提供了可能。因此，本项目拟以拟南芥为材料，利用激光共聚焦显微镜法测定蔗糖运输途径不同节点细胞跨质膜pH梯度，为确定跨质膜pH梯度与蔗糖转运功能关系的研究奠定基础。

蔗糖是植物重要的光合产物，其运输和分配与经济产量密切相关。在体内蔗糖质外体运输途径中，蔗糖跨质膜吸收或输出都受跨质膜pH梯度调节。然而，细胞质膜pH梯度都是内高外低。可能的解释是跨质膜pH梯度的调节作用与梯度的大小有关，而蔗糖运输途径不同部位的不同类型细胞质膜pH梯度存在差异。激光共聚焦显微镜测定pH技术、液相色谱测定蔗糖技术结合拟南芥蔗糖转运蛋白突变体的利用为研究这个问题提供了可能。本项目利用共聚焦显微镜观察了pH荧光指示剂在拟南芥叶片组织分布情况，表明可以用来检测组织的pH变化。但是本项目需要了解质膜两侧的pH，目前还没有发现适合同时监测质膜两侧pH变化的荧光指示剂，这成为该领域研究深入的瓶颈。拟南芥蔗糖转运蛋白突变体atsuc2、atsuc3、atsuc4、atsuc9、及atsuc3/atsuc9双突变体都影响蔗糖含量，而且，这些突变体的蔗糖含量受IAA、ABA、低温、渗透胁迫和盐胁迫的影响。因此，这些材料可以用来研究跨质膜pH梯度变化与蔗糖转运方向和速率的关系。AtSUC2 和AtSUC4是拟南芥蔗糖转运蛋白基因家族中响应高盐、渗透、低温和外源ABA处理诱导的关键基因，并且参与ABA依赖的信号转导途径。它们的缺失导致叶组织蔗糖的积累、根组织蔗糖含量的降低。相关内容发表在SCI收录期刊Physiologia Plantarum。