Regulation of Sulfate Assimilation in Plants

硫酸盐同化是无机硫酸盐（SO 42-）被还原用于半胱氨酸合成的途径。半胱氨酸是一种重要的氨基酸，具有多种功能。本研究着重于其作为谷胱甘肽前体的作用，谷胱甘肽是植物中重要的抗氧化剂，APS还原酶催化硫酸盐同化的一个重要步骤，它从5-腺苷酰硫酸盐（APS）产生亚硫酸盐（SO_（32-））。实验证明APS还原酶是通过氧化作用而被激活的。建议的假设是，APS还原酶在氧化应激条件下谷胱甘肽合成的调节中起着关键作用。因此，它可能是植物对氧化胁迫反应的一个重要组成部分。本研究将通过探讨APS还原酶调节的机制和生理效应来验证该项目假设。APS还原酶基因已经从几种不同的植物物种中克隆。每一种都将被氧化条件调节的能力进行研究。据信，APS还原酶调节的机制依赖于蛋白质中可以形成二硫键的两个半胱氨酸残基。将分析酶的半胱氨酸残基的状态。最后，我们还将研究通过在转基因植物中表达细菌同源物绕过APS还原酶步骤的生理效应，这项工作将为植物对氧化应激反应的一个重要方面，即谷胱甘肽合成的调节机制提供新的见解。APS还原酶是由氧化应激条件激活的一小组酶之一。该系统的新奇和与氧化应激的联系是进一步研究APS还原酶的令人信服的原因。

Sulfate assimilation is the pathway by which inorganic sulfate (SO42-) is reduced for cysteine synthesis. Cysteine is an important amino acid with many different functions. This proposal focuses on its role as the precursor of glutathione an important antioxidant in plants.The enzyme APS reductase, which produces sulfite (SO32-) from 5-adenylylsulfate (APS), catalyzes an essential step in sulfate assimilation. Experimental evidence has been obtained that APS reductase is activated by oxidation. The proposal hypothesis is that APS reductase plays a key role in regulation of glutathione synthesis under conditions of oxidative stress. Therefore, it may be an important component in the plant response to oxidative stress.In the work proposed the project hypothesis will be tested by exploring the mechanism and physiological effect of APS reductase regulation. APS reductase genes have been cloned from several different plant species. Each will be studied for the ability to be regulated by oxidative conditions. It is believed that the mechanism of APS reductase regulation relies on two cysteine residues in the protein that can form a disulfide bond. The state of the cysteine residues of the enzyme will be analyzed. Finally, the physiological effect of bypassing the APS reductase step by expressing bacterial homologs in transgenic plants will also be studied.This work will provide new insight into an important facet of plant response to oxidative stress, the mechanism for regulation of glutathione synthesis. APS reductase is one of a small group of enzymes that are activated by oxidative stress conditions. The novelty of this system and the connection with oxidative stress are compelling reasons for further study of APS reductase.