A chlorate‐hypersensitive, high nitrate/chlorate uptake mutant of Arabidopsis thaliana

Seedlings hypersensitive to root‐supplied chlorate were isolated from mutagentreated populations of A. thaliana L. (Heynh.). Characterization of one such mutant is described in the present report. The mutant (designated C1), accumulated greater than normal quantities of nitrate in the leaves and took up nitrate and chlorate rapidly in uptake experiments. The nitrate and chlorate uptake rates of this mutant were substantially higher than for eight other genotypes tested in our laboratory. Nitrate reductase (NR; EC 1.6.6.1) activity, glutamine synthetase (GS; EC 6.3.1.2) activity, and cytochrome c reductase (CCR) activity of NR were slightly elevated in young plants. The altered nitrate uptake rates may represent the primary lesion of this mutant. Its phenotype is substantially different from that of a previously described chlorate hypersensitive mutant (C4) and is not controlled by the same locus.