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Crop Science Abstract -

Characterization of Nitrate Reductase-Deficient Mutants in Pea1


This article in CS

  1. Vol. 22 No. 2, p. 389-393
    Received: Feb 20, 1981

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  1. R. L. Warner,
  2. A. Kleinhofs and
  3. F. J. Muehlbauer2



Three nitrate reductase-deficient pea (Pisum sativum L.) mutants which were selected from segregating M2 population by a qualitative in vivo assay, were characterized for in vitro nitrate reductase (NADH and FMNH2), nitrite reductase, cytochrome c reductase, and xanthine dehydrogenase activities. In vitro NADH-nitrate reductase activity in leaves of mutant A300 was 20% while the activities of mutants A317 and A334 were less than 6% of the wild type. Nitrate reductase activities in the roots were similar to the leaf activities in all three mutants. In vitro FMNH2-nitrate reductase activities of all three mutants were lower than the NADH activities. Nitrite reductase activities in the mutants were elevated (192 to 232 % of the wild type) and were not produced constitutively. All three mutants and the wild type have nitrate induced cytochrome c reductase activities indicating that the nitrate reductase protein in the mutants has the cytochrome c reductase partial activity but is incapable of nitrate reduction. Xanthine dehydrogenase activity was detected in A317, A334 and the wild type but not in A300.

Mutants A317 and A334 are allelic and are assigned the gene designation nar1. A300 represents a second locus and is assigned the gene designation nar2. Both nar1 and nat2 exhibit incomplete dominance and do not appear to be closely linked. The absence of xanthine dehydrogenase in A300 suggests that nat2 is a gene controlling the molybdo-cofactor component of nitrate reductase and perhaps other molybdo-enzymes. Nar1 may be the nitrate reductase structural gene.

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