Salminen S O, Streeter J G
Department of Agronomy, Ohio State University, 1680 Madison Avenue, Wooster, Ohio 44691.
Plant Physiol. 1992 Oct;100(2):597-604. doi: 10.1104/pp.100.2.597.
The aim of the work reported here was to ascertain that the patterns of labeling seen in isolated bacteroids also occurred in bacteroids in intact nodules and to observe early metabolic events following exposure of intact nodules to (14)CO(2). Intact nodules of soybean (Glycine max L. Merr. cv Ripley) inoculated with Bradyrhizobium japonicum USDA 110 and pea (Pisum sativum L. cv Progress 9) inoculated with Rhizobium leguminosarum bv viciae isolate 128C53 were detached and immediately fed (14)CO(2) for 1 to 6 min. Bacteroids were purified from these nodules in 5 to 7 min after the feeding period. In the cytosol from both soybean and pea nodules, malate had the highest radioactivity, followed by citrate and aspartate. In peas, asparagine labeling equaled that of aspartate. In B. japonicum bacteroids, malate was the most rapidly labeled compound, and the rate of glutamate labeling was 67% of the rate of malate labeling. Aspartate and alanine were the next most rapidly labeled compounds. R. leguminosarum bacteroids had very low amounts of (14)C and, after a 1-min feeding, malate contained 90% of the radioactivity in the organic acid fraction. Only a trace of activity was found in aspartate, whereas the rate of glutamate and alanine labeling approached that of malate after 6 min of feeding. Under the conditions studied, malate was the major form of labeled carbon supplied to both types of bacteroids. These results with intact nodules confirm our earlier results with isolated bacteroids, which showed that a significant proportion of provided labeled substrate, such as malate, is diverted to glutamate. This supports the conclusion that microaerobic conditions in nodules influence carbon metabolism in bacteroids.
本文报道的研究目的是确定在分离的类菌体中观察到的标记模式在完整根瘤中的类菌体中是否也会出现，并观察完整根瘤暴露于（14）CO（2）后的早期代谢事件。将接种了日本慢生根瘤菌USDA 110的大豆（Glycine max L. Merr. cv Ripley）完整根瘤和接种了豌豆根瘤菌蚕豆生物型分离株128C53的豌豆（Pisum sativum L. cv Progress 9）完整根瘤摘下，立即用（14）CO（2）饲喂1至6分钟。饲喂期结束后5至7分钟，从这些根瘤中纯化类菌体。在大豆和豌豆根瘤的胞质溶胶中，苹果酸的放射性最高，其次是柠檬酸和天冬氨酸。在豌豆中，天冬酰胺的标记量与天冬氨酸相等。在日本慢生根瘤菌类菌体中，苹果酸是标记最快的化合物，谷氨酸的标记速率是苹果酸标记速率的67%。天冬氨酸和丙氨酸是其次标记最快的化合物。豌豆根瘤菌类菌体的（14）C含量非常低，饲喂1分钟后，苹果酸在有机酸部分中含有90%的放射性。在天冬氨酸中仅发现微量活性，而饲喂6分钟后，谷氨酸和丙氨酸的标记速率接近苹果酸的标记速率。在所研究的条件下，苹果酸是供应给这两种类菌体的标记碳的主要形式。这些完整根瘤的结果证实了我们早期对分离类菌体的研究结果，即所提供的标记底物（如苹果酸）中有很大一部分被转移到谷氨酸中。这支持了根瘤中的微需氧条件影响类菌体碳代谢的结论。
