Biophysical and Biochemical Studies on Ion Transport in Plants

这个由资金资助的项目继续测试离子在植物细胞膜上传输的化学渗透假说。已证实位于质膜和液泡膜上的H+转运ATPase建立了H+的电化学势梯度，为其他离子和有机小分子通过质子共转运系统的转运提供了驱动力。以番茄和玉米根为实验材料。利用pH梯度和膜电位的荧光探针，结合放射性示踪剂，研究了钠、钾和硝酸盐在分离的质膜囊泡中的共转运系统的存在。在诱导硝酸盐运输后，将尝试确定质膜中硝酸盐的载体蛋白。从原生质体获得的全细胞电压钳记录是用紧密密封的贴片管获得的。这项技术将被用来研究电生H+-ATPase对番茄根细胞质膜电位和电导的贡献。通过用不同的溶液灌流贴片吸管来控制“细胞质”的pH和ATP水平，将被用来比较生电泵的行为和H+-ATPase的已知动力学特性。这项工作的意义在于阐明植物体内离子运输的机制，这是一个至关重要的代谢过程。它通过离子传输吸收营养物质，控制酸度，为生物合成提供原料。

The funded project continues testing a chemiosmotic hypothesis for the transport of ions across plant cell membranes. It is postulated that the H+ -translocating ATPases, which have been demonstrated to be located in the plasma membrane and the tonoplast, set up electrochemical potential gradients of H+ which provide the driving force for the transport of other ions and small organic molecules via proton cotransport systems. Tomato and corn roots are the experimental material. Fluorescent probes for pH gradients and membrane potentials are used in conjunction with radioactive tracers to investigate the occurence of cotransport systems for sodium, potassium and nitrate in isolated plasma membrane vesicles. An attempt will be made to identify the carrier protein for nitrate in the plasma membrane following induction of nitrate transport. Whole- cell voltage clamp recordings from protoplasts are being obtained with tight-seal patch pipets. This technique will be used to investigate the contribution of the electrogenic H+ -ATPase to the membrane potential and conductance of the tomato root cell plasma membrane. Control of the "cytoplasmic" pH and ATP level by perfusion of the patch pipet with different solutions will be used to compare the behavior of the electrogenic pump with the known kinetic properties of the H+ -ATPase. The significance of this work lies in elucidating the mechanism of ion transport in plants, a process of crucial metabolic importance. It is through ion transport that nutrients are absorbed, acidity is controlled and starting materials are provided for biosynthesis.***//