Vance C P, Boylan K L, Maxwell C A, Heichel G H, Hardman L L
Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55108.
Plant Physiol. 1985 Aug;78(4):774-8. doi: 10.1104/pp.78.4.774.
Nodulated and denodulated roots of adzuki bean (Vigna angularis), soybean (Glycine max), and alfalfa (Medicago sativa) were exposed to (14)CO(2) to investigate the contribution of nodule CO(2) fixation to assimilation and transport of fixed nitrogen. The distribution of radioactivity in xylem sap and partitioning of carbon fixed by nodules to the whole plant were measured. Radioactivity in the xylem sap of nodulated soybean and adzuki bean was located primarily (70 to 87%) in the acid fraction while the basic (amino acid) fraction contained 10 to 22%. In contrast, radioactivity in the xylem sap of nodulated alfalfa was primarily in amino acids with about 20% in organic acids. Total ureide concentration was 8.1, 4.7, and 0.0 micromoles per milliliter xylem sap for soybean, adzuki bean, and alfalfa, respectively. While the major nitrogen transport products in soybeans and adzuki beans are ureides, this class of metabolites contained less than 20% of the total radioactivity. When nodules of plants were removed, radioactivity in xylem sap decreased by 90% or more. Pulse-chase experiments indicated that CO(2) fixed by nodules was rapidly transported to shoots and incorporated into acid stable constituents. The data are consistent with a role for nodule CO(2) fixation providing carbon for the assimilation and transport of fixed nitrogen in amide-based legumes. In contrast, CO(2) fixation by nodules of ureide transporting legumes appears to contribute little to assimilation and transport of fixed nitrogen.
将小豆（Vigna angularis）、大豆（Glycine max）和苜蓿（Medicago sativa）的结瘤根和去瘤根暴露于¹⁴CO₂中，以研究根瘤CO₂固定对固定氮同化和运输的贡献。测量了木质部汁液中放射性的分布以及根瘤固定的碳在整株植物中的分配情况。结瘤大豆和小豆木质部汁液中的放射性主要（70%至87%）存在于酸性组分中，而碱性（氨基酸）组分中含有10%至22%。相比之下，结瘤苜蓿木质部汁液中的放射性主要存在于氨基酸中，约20%存在于有机酸中。大豆、小豆和苜蓿木质部汁液中总脲类化合物浓度分别为每毫升8.1、4.7和0.0微摩尔。虽然大豆和小豆中主要的氮运输产物是脲类化合物，但这类代谢产物所含放射性不到总放射性的20%。去除植物根瘤后，木质部汁液中的放射性降低了90%或更多。脉冲追踪实验表明，根瘤固定的CO₂迅速运输到地上部并整合到酸稳定成分中。这些数据与根瘤CO₂固定在为酰胺类豆科植物中固定氮的同化和运输提供碳方面的作用一致。相比之下，运输脲类化合物的豆科植物根瘤的CO₂固定似乎对固定氮的同化和运输贡献很小。
