RUI: Oxygen Defense Mechanisms in Legume Root Nodules

由于固氮酶对氧的敏感性以及固氮所需的强烈还原条件，固氮微生物特别容易受到氧气的伤害。在豆科植物根瘤中，特殊的防御酶包括超氧化物歧化酶、抗坏血酸过氧化物酶、单脱氢抗坏血酸还原酶和抗坏血酸-谷胱甘肽循环中的其他酶的作用可将氧毒性降至最低。这项研究的主要目的是确定参与氧气防御的酶的特征，确定这些酶的亚细胞定位，确定这些酶是否是根瘤特异的，并检查氧气防御和固氮之间联系的关键。酶学研究将包括纯化和双向凝胶电泳，然后进行免疫学检测。纯化的酶将被用来制备抗血清，用于使用光学和电子显微镜进行亚细胞定位的免疫学检测。无效的结节将接受氧气防御酶缺乏的检查。具有有效根瘤的植物将生长在不同氧浓度的根大气中，并将监测根瘤防御机制的反应。豆类提供世界上相当大一部分蛋白质，而不需要氮肥。加强这些作物以及其他作物的固氮，是增加对氮肥依赖的一个有吸引力的替代方案。为了实现这种改进，我们必须了解氮结核生理学的生物化学和生理学。这项研究调查了负责将这些根瘤中的氧毒性降至最低的酶。更好地了解这些酶可能会允许对它们的操纵，这反过来可能会增加作物产量。此外，它们可能是未来在作物物种中发展新的固氮协会所必需的。

Nitrogen-fixing organisms are especially vulnerable to oxygen damage due to the oxygen sensitivity of nitrogenase and to the strong reducing conditions required to fix nitrogen. In legume root nodules, oxygen toxicity is minimized by action of special defense enzymes including superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase and other enzymes of the ascorbate-glutathione cycle. The main objectives of this research are to characterize the enzymes involved in oxygen defense, to determine the subcellular localization of these enzymes, to determine if these enzymes are nodule-specific, and to examine the criticality of the link between oxygen defense and nitrogen fixation. Enzymological studies will involve purification and 2-D gel electrophoresis followed by immunological detection. Purified enzymes will be used to prepare antisera for immunological detection of subcellular localization using both light and electron microscopy. Ineffective nodules will be examined for deficiencies in oxygen defense enzymes. Plants with effective nodules will be grown in root atmospheres of various oxygen concentrations and the response of nodule defense mechanisms will be monitored.%%% Legumes provide a substantial portion of the world's protein without requiring nitrogen fertilizer. The enhancement of nitrogen fixation in these, as well as other crop plants, is an attractive alternative to increasing reliance on nitrogen fertilizers. In order for such improvements to come about we must understand both the biochemistry and physiology of nitrogen nodule physiology. This research investigates the enzymes responsible for minimizing oxygen toxicity in these nodules. A better understanding of these enzymes may allow for their manipulation which may, in turn, increase crop yields. Furthermore, they may be required for the future development of new nitrogen-fixing associations in crop species.***//