Biochemical Nitrogen Fixation Studies. IV. Experiments with Excised Legume Nodules

Abstract

Excised root nodules of sweet clover, cowpea, crown vetch. soybean, and hairy vetch were maintained in culture solns. in the laboratory and analyses to determine increase in combined N were made by both gasometric and Kjeldahl methods. No N fixation was observed with whole or crushed nodules kept in Warburg vessels at 28[degree]C in various gas mixtures and in culture solns. containing either glucose, sucrose or mannite. A slight but probably insignificant increase in N was obtained where nodules were kept in a sugar-mineral medium for 1 to 3 days at either 4[degree]C or 12[degree]C. A few similar expts. with oxalacetic acid added to the medium gave negative or inconclusive results. Pure cultures of rhizobia supplied with oxalacetic acid also fixed no N. Numerous expts. gave no evidence that the juices extracted from nodules and then sterilized can fix N. These results are in agreement with those obtained by Roberg using Azotobacter juices but not with those of Bach who reported comparatively large fixations with the enzymes from this organism.