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Tissue culture isolation of a second mutant locus for increased threonine accumulation in maize


Regenerable maize (Zea mays L.) tissue cultures were selected for ability to grow in the presence of inhibitory (1.0–1.5 mM) concentrations of L-lysine plus L-threonine. Testcross kernels from one regenerated plant (LT20) segregated for wild-type and high free threonine concentration in a 1∶1 ratio consistent with a single dominant gene for high free threonine. Free threonine concentrations (nmol/mg dry weight) increased an average of 29-fold in bulked F2 kernel samples from heterozygous mutant plants, and the total (free plus protein-bound) threonine concentration increased 68%. Increases in protein-bound methionine, lysine and glycine concentrations were also noted, suggesting a possible effect of the mutation on protein concentration and composition. Allelism tests with a previously selected mutant line, Ltr *19, showed that two unlinked, codominant genes conditioned the high free threonine phenotype. Based on a separate study of aspartate kinase feedback inhibition characteristics in the two mutant lines, we propose that the mutant alleles [gene and allele designations are according to guidelines for maize genetic nomenclature (Burnham et al. 1975)] be designated Ask-LT19 and Ask2-LT20 for the Ltr *19 and LT20 mutants, respectively.

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Communicated by F. Salamini

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Diedrick, T.J., Frisch, D.A. & Gengenbach, B.G. Tissue culture isolation of a second mutant locus for increased threonine accumulation in maize. Theoret. Appl. Genetics 79, 209–215 (1990).

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Key words

  • Tissue culture mutant selection
  • Amino acid biosynthesis
  • Lysine plus threonine resistance
  • Aspartate kinase
  • Maize