Effect of Inoculation with Various Rhizobia Strains on the Fatty Acid Composition of Peribacteroid and Bacteroid Membranes of the Nodule Symbiosomes

The fatty acid (FA) composition of bacteroid and peribacteroid membranes was studied in the symbiotic pairs differing in their nitrogen-fixing efficiency; the results are compared with the FA composition of plasmalemma and free-living rhizobia. The experiments involved lupine plants inoculated with strains of Bradyrhizobium lupini359a (Nod⁺Fix⁺) and 400 (Nod⁺Fix L) manifesting high and low nitrogen-fixing efficiency, respectively, and broad bean plants inoculated with strains of Rhizobium leguminosarum97 (Nod⁺Fix⁺) and 87 (Nod⁺Fix L) of high and low nitrogen-fixing efficiency, respectively. We showed that the rhizobia of the strains 359a and 97 were able to form nodules with peribacteroid membranes containing FA mainly or exclusively of plant origin. These strains were able to develop effective symbiotic pairs with legume plants. The use of strains 400 and 87 resulted in the formation of nodules with peribacteroid membranes containing typical bacterial (branched-chain) FAs; these strains were characterized by an ineffective symbiosis.     

Catalase Activity of Nodules in the Ureide- and Amide-transporting Legume Plants

The relations of catalase activity to the efficiency of symbiotic dinitrogen fixation and leghemoglobin (Lb) content were investigated in roots and nodules of several legume plant species together with the catalase distribution between the inner bacteroidal and the outer cortical nodule tissues. The catalase activity in the nodules exceeded that of the roots of the amide- and ureide-synthesizing plant species by one and two orders of magnitude. During the growth period, catalase activity and Lb content changed in parallel and reached their highest levels early in the stage of flowering or fruit formation, depending on plant species. In the case of effective symbiosis, catalase activity in the nodules was 2.5–5 times higher than in the case of ineffective symbiosis. Catalase activity in the bacteroidal zone of the nodules was several times higher than that of the cortical tissue, and two nodule tissues differed in catalase activity more notably in the plant species exporting ureides. The authors suggest that high catalase activity in the nodules, especially in their bacteroidal zone, is essential for the efficient functioning of the symbiotic system of dinitrogen fixation in both ureide- and amide-transporting plants.     

Symbiotic Nitrogen Fixation and Ammonium Nitrogen Assimilation in rrrbrb-, rrRbRb-, and RRrbrb-Pea Mutants

Wrinkled-seeded pea mutants (Pisum sativum L., genotypes rrrbrb-, rrRbRb-, and RRrbrb-) have seeds with reduced, but different, starch content and modified starch properties. Analysis of these mutants revealed an enhanced capacity of root nodules for symbiotic nitrogen fixation and of host plant organs for assimilation of ammonium nitrogen. This observation was confirmed by morphological data on organization of symbiotic system, by elevated nitrogenase activity, high protein accumulation in plants due to nitrogen fixation, and by enhanced activity of glutamine synthase in leaves and glutamate dehydrogenase in roots of mutants, as compared with the organs of wild-type pea. It is supposed that the aforementioned advantages of mutants are related to accumulation in seeds of elevated protein reserves that satisfy their demand for nitrogen during formation of symbiotic systems.     

Chemical characterization of effective and ineffective strains of Rhizobium leguminosarum bv. viciae

Chemical composition of lipopolysaccharide (LPS) isolated from an effective (97) and ineffective (87) strains of R. l. viciae has been determined. LPS preparations from the two strains contained: glucose, galactose, mannose, fucose, arabinose, heptose, glucosamine, galactosamine, quinovosamine, and 3-N-methyl-3,6-dideoxyhexose, as well as glucuronic, galacturonic and 3-deoxyoctulosonic acid. The following fatty acids were identified: 3-OH 14:0, 3-OH 15:0, 3-OH 16:0, 3-OH 18:0 and 27-OH 28:0. The ratio of 3-OH 14:0 to other major fatty acids in LPS 87 was higher that in LPS 97. SDS/PAGE profiles of LPS indicated that, in lipopolysaccharides, relative content of S form LPS I to that of lower molecular mass (LPS II) was much higher in the effective strain 97 than in 87. All types of polysaccharides exo-, capsular-, lipo, (EPS, CPS, LPS, respectively) examined possessed the ability to bind faba bean lectin. The degree of affinity of the host lectin to LPS 87 was half that to LPS 97. Fatty acids (FA) composition from bacteroids and peribacteroid membrane (PBM) was determined. Palmitic, stearic and hexadecenoic acids were common components found in both strains. There was a high content of unsaturated fatty acids in bacteroids as well as in PBM lipids. The unsaturation index in the PBM formed by strain 87 was lower than in the case of strain 97. Higher ratio of 16:0 to 18:1 fatty acids was characteristic for PMB of the ineffective strain.