Recent studies on the Rhizobium-legume symbiosis

Abstract

This brief paper summarizes our research progress since the 7th International Congress on Nitrogen Fixation at Köln, West Germany. We published studies reported at that meeting on the structural similarities and differences between the capsular acidic heteropolysaccharide (CPS) of Rhizobium trifolii and R. leguminosarum (4), and the effect of interspecies transfer of Rhizobium host-specific nodulation genes on CPS structure and in situ binding by trifoliin A lectin (5). We also published on the application of computer-aided image analysis for studies of the Rhizobiurn-legume symbiosis (2). Interesting measurements reported in that paper include: (i) R. leguminosarum bacteroids are 7.2 times the volume of vegetative bacteria within pea nodules, (ii) the average vertex angle of root hair branching induced by R. trifolii on white clover is 67°, (iii) R. trifolii rotates its flagella at 330 rpm and swims at 53 µm/sec in the external root environment of agar less Fahraeus slide cultures of white clover, (iv) inoculation of white clover roots with R. trifolii leads to a 35% increase in cytoplasmic streaming in root hairs, and (v) white clover root hairs elongate during active growth at an average rate of 38 µm/nr.