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). https://doi.org/10.1007/BF00225953
- Tissue culture mutant selection
- Amino acid biosynthesis
- Lysine plus threonine resistance
- Aspartate kinase