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A mutation that blocks exopolysaccharide synthesis prevents nodulation of peas by Rhizobium leguminosarum but not of beans by R. phaseoli and is corrected by cloned DNA from Rhizobium or the phytopathogen Xanthomonas (1986)

Borthakur, D. ; Barber, C. E. ; Lamb, J. W. ; [et al.]

Springer

Molecular genetics and genomics 203 (1986), S. 320-323

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ISSN: 1617-4623

Keywords: Exopolysaccharide ; Legume ; Nodules ; Rhizobium ; Xanthomonas

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary A Tn5-induced mutant strain of R. phaseoli which failed to synthesize exopolysaccharide (EPS) was isolated and was shown to induce normal nitrogen-fixing nodules on Phaseolus beans, the host of this Rhizobium species. The corresponding wild-type Rhizobium DNA was cloned in a wide host-range vector and by isolating Tn5 insertions in this cloned DNA, mutations in a gene termed pss (polysaccharide synthesis) were isolated. These were introduced by marker exchange into near-isogenic strains of R. leguminosarum and R. phaseoli which differed only in the identity of their symbiotic plasmids. Whereas the EPS-deficient mutant strain of R. phaseoli induced normal nitrogen-fixing nodules on Phaseolus beans, the same mutation prevented nodulation of peas by a strain of R. leguminosarum which normally nodulates this host. Further, it was found that DNA cloned from the plant pathogen Xanthomonas campestris pathover campestris could correct the defect in EPS synthesis in R. leguminosarum and R. phaseoli and also restored the ability to nodulate peas to the pss::Tn5 mutant strain of R. leguminosarum.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00333974

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Adsorption of N-phenylglycine on hydroxyapatite: Role in the bonding procedure of a restorative resin to dentin (1987)

Misra, D. N. ; Johnston, A. D.

Hoboken, NJ : Wiley-Blackwell

Journal of Biomedical Materials Research 21 (1987), S. 1329-1339

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ISSN: 0021-9304

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine , Technology

Notes: The adsorption of N-phenylglycine (NPG) onto synthetic hydroxyapatite from ethanol solutions was studied to elucidate the role of surface-active moieties in determining the character of adsorption, and to explore the role of NPG in a bonding procedure of restorative resin to dentin. The adsorption isotherm of N-phenylglycine is reversible (and Langmuirian) from ethanol (99.8%). At maximum adsorption the phenyl rings of the adsorbed molecules lie flat on the surface and the carboxylate oxygens and amino nitrogens are anchored to the surface. The N-phenylglycine serves as an amine accelerator since the peroxide containing monomer polymerizes with the adsorbate-covered apatite. The diametral tensile strength of this composite is approximately equal to the composite filled with untreated apatite. The role of various factors contributing to adhesive strength in the bonding procedure is also discussed.

Additional Material: 2 Ill.