Development of Discontinuous Size Classes of Nodules of Glycine max

Rhizobium japonicum, Glycine max, Nodules Size Classes, Nitrogenase, Leghaemoglobin In order to characterize developmental stages of nodules of Glycine max nitrogenase activity in the variety Caloria, infected with Rhizobium japonicum 61-A -101, was studied in atmospheres with 19 and 40% 0 2. By the enhancement effect at 40% 0 2 four stages of nodule development could be separated. Nitrogenase activity depends also among other things on nodule size. 3 4 maxima in nodule number and nodule weight were found by fractionating nodules in 12 different size classes. Discontinuous size distribution was found with medium aged and old effective nodules. Nodule number (20 to 30) of effective nodules per plant remains constant. Ineffective nodules remain far smaller than the effective ones, the number increases to more than 140 per plant and only one discontinuous size classe was observed. Bacteroids and plant cytoplasm from nodules of some size classes are characterized by their leghaemoglobin content and specific activity of enzymes of nitrogen metabolism such as aspartate aminotransferase (E.C. 2.6.1.1), glutamate dehydrogenase (E.C. 1.4.1.2) and alanine de­ hydrogenase (E.C. 1.4.1.1). The data in the various size classes are similar both in the bacteroids and the plant cytoplasm, however, leghaemoglobin content and specific activity of the bacterial enzyme alanine dehydrogenase are positively correlated with the increasing nodule size.