Signal Transduction Across Plant Plasma Membranes

该实验室以前的结果表明，植物防御反应的激发子与植物细胞表面的受体结合，并在0-8分钟内刺激过氧化氢的爆发。这种过氧化氢的突然产生不仅可以破坏某些致病化合物，还可能抑制随后的植物抗毒素的产生。本研究的下一个目标是表征氧化猝发，确定其在触发植物抗毒素生物合成中的作用，评估其他防御化合物是否由氧化猝发诱导，并确定参与其合成的酶和底物。最近的结果还表明，激发子分子与植物细胞表面的激发子受体结合后，通过内吞作用被内化。在进一步的实验中，将研究受体内化的动力学，并将监测其从细胞表面移动到最终细胞内目的地的路径。不同激发子的受体是否遵循相同的途径也将被评估。最后，研究发现，植物细胞具有生物素受体，如果大分子首先与生物素共价衍生，大分子可以通过生物素受体介导的内吞作用进入活的植物细胞。将探索利用这种途径将酶、核酸、毒素和抗体等输送到活的植物细胞中。正如高等动物有良好的免疫反应来抵御病原体一样，高等植物也有防御反应，使它们能够抵抗入侵和破坏。植物防御反应的调控机制是一个非常重要的基本问题，到目前为止，人们对此知之甚少。在NSF先前的支持下，Low博士和Heinstein博士发现，大豆细胞暴露在防御反应的化学触发物(“激发子”)下后，植物细胞很快就会产生过氧化氢。这项研究的进一步目标是阐明过氧化氢在防御反应中的作用，并寻找有关植物暴露于潜在病原体和植物产生保护性化学物质之间的事件序列的其他线索。这个项目的结果将有助于我们理解调节植物防御反应的细胞信号机制。

Prior results from this laboratory have shown that elicitors of a plant's defense response bind to receptors on the plant cell surface and within 0-8 minutes stimulate a burst of hydrogen peroxide. This sudden production of hydrogen peroxide serves not only to destroy certain pathogenic compounds but may also stiimulate subsequent phytoalexin production. The next goals of this research are to characterize the oxidative burst, determine its role in triggering phytoalexin biosynthesis, evaluate whether other defense compounds are induced by the oxidative burst, and identify the enzymes and substrates involved in its synthesis. Recent results also indicate that the elicitor molecule is internalized via endocytosis following association with its receptor on the plant cell surface. In further experiments, the kinetics of internalization of the receptor will be examined, and its path will be monitored as it moves from the cell surface to its final intracellular destination . Whether receptors for different elicitors follow identical pathways will also be evaluated. Finally, it has been found that plant cells have receptors for biotin and that macromolecules can be delivered into a living plant cell via biotin receptor-mediated endocytosis if the macromolecules are first covalently derivatized with biotin. The use of this pathway to deliver enzymes, nucleic acids, toxins and antibodies, etc into living plant cells will be explored. Just as higher animals have well developed immune responses to defend against pathogens, higher plants also have defense responses that allow them to resist invasion and damage. The mechanisms by which plant defense responses are regulated is a very important fundamental problem about which, thus far, little is known. With prior NSF support, Drs. Low and Heinstein discovered that exposure of soybean cells to a chemical trigger ("elicitor") of a defense response is followed very quickly by production of hydrogen peroxide by the plant cells. The further goals of this research are to clarify the role of hydrogen peroxide in the defense response, and to pursue other leads concerning the sequence of events between exposure of a plant to a potential pathogen and the production by the plant of protective chemicals. The results of this project should contribute to our understanding of the cellular signaling mechanisms that regulate plant defense responses.