Some aspects of symbiotic nitrogen fixation in Vicia cracca L. (Leguminosae)

Niles, A. M. (1984) Some aspects of symbiotic nitrogen fixation in Vicia cracca L. (Leguminosae). Masters thesis, Memorial University of Newfoundland.

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Abstract

Studies were undertaken to characterize the symbiosis between an uncultivated legume, Vicia cracca L., and a strain of Rhizobium bacteria isolated from its root nodules. -- Root nodules were found to be elongate and often branched at maturity. Tritiated-thymidine incorporation studies, monitored by autoradiography, indicated that nodules develop from an apically-located meristem. Nitrogen fixation, measured by acetylene reduction, occurred at rates commensurate with values reported for other legumes. Vicia cracca seeds and plants are small and can be conveniently cultured in vitro but a rigorous scarification procedure, immersion in concentrated sulfuric acid, was required to produce appreciable germination rates. Sulfuric acid simultaneously carified and surface-sterilized Vicia cracca seeds. This permitted nodulation of V. cracca, by selected Rhizobium strains, to be conveniently studied. -- The Rhizobium isolate, referred to as R. sp. VC 2, was identified as a wild strain of Rhizobium leguminosarum. Studies were undertaken to characterize the bacterium with respect to carbon and nitrogen nutrition and with respect to the effects of temperature and pH on growth. A wide variety of carbon and nitrogen sources was used by R. sp. VC 2. Total growth of shake cultures was significantly affected by carbon and nitrogen source and markedly dependent on the initial pH of the growth medium. Total growth of bacteria in shake culture, at pH values below 7.0, was found to be greater at 24 C than at 30 C. The cell surface of R. sp. VC 2 was shown to possess receptor sites for a lectin from V. cracca seeds. The lectin was extracted from V. cracca seeds by affinity chromatography and labelled with fluorescent isothiocyanate (FITC). Nitrogen fixing activity was induced in free-living cultures of Rhizobium sp. VC 2. A number of carbohydrates, alone add in combination, supported nitrogen fixation. R. sp. VC 2 nodulated V cracca as efficiently as two commercial strains of Rhizobium leguminosarum. - V. cracca seedlings, being small, could be easily cultured in vitro and nodulated by Rhizobium leguminosarum. These attributes permit the V. cracca - Rhizobium leguminosarum symbiosis to be used as a convenient model for the Pisum sativum (pea) - Rhizobium leguminosarum symbiosis. Uncultivated V. cracca nodules could be used as a source of new genetic material for commercial producers of Rhizobium inocula. Also, the Vicia cracca - Rhizobium leguminosarum symbiosis has potential to be used in land reclamation and land maintenance projects.

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