Original Communications ß-Carboline Alkaloids from Ribes nigrum L. The deletion mutant Bradyrhizobium japonicum AP22 produces a structurally altered exo-polysaccharide. The nodulation of two cultivars each of Glycine max and Glycine soja, and cultivars of Macroptilium atropurpureum and Vigna radiata, infected with this mutant was examined in order to analyze the role of the exopolysaccharide in the infection process of plants with a determinate nodule type. All host plants analyzed exhibited delayed nodulation and formed fewer nodules per plant. The extent of the impairments depended on the genotype of the host plant. Morphological studies confirmed these results. In V radiata later Steps in nodule development proceeded without further disturbances, whereas with G. soja PI 407287 minor changes were detected. In contrast, the inoculation of G. soja PI 468397 and M. atropurpureum lead to the formation of nodules most of which were not infected by Bradyrhizobium japonicum AP22 (Inf-). However, on M. atropurpureum at least some effective nitrogen-fixing nodules developed. Such nodules did not emerge from G soja PI 468397. Inf-nodules were arrested in an early stage of nodule development, and Symptoms of plant defense responses were observed.