Chlorate is an analog of nitrate and can be used to select for mutants which are deficient in nitrate reductase or transport (see e.g. Wilkinson and Crawford, 1993).

Nitrate reductase readily reduces chlorate to chlorite which is toxic.

As noted earlier, a chlorate resistant mutant (chl1) of Arabidopsis has been identified which are defective in nitrate transport, but this may be the low-affinity nitrate transporter. Chlorate may not be a useful analog for the root high-affinity nitrate transport system (Kosola and Bloom, 1996).

Light acts both directly as a signal and indirectly through photosynthesis to regulate the expression of genes encoding nitrate reductase (NR). A chlorate-resistant mutant of Arabidopsis (cr88) has recently been isolated which is defective in the regulation of NR gene expression. The response of NR2, but not NR1 or the gene encoding nitrite reductase (NiR) was impaired in cr88. The light regulation of the genes encoding the chlorophyll a/b binding protein and the small subunit of ribulose-bisphosphate carboxylase/oxygenase was also impaired. cr88 is defective in red-light mediated deetiolation (Lin and Cheng, 1997). Nitrate and sucrose induction processes are retained in cr88 (Lin and Cheng, 1997).

Kosola KR, Bloom AJ 1996 Chlorate as a transport analog for nitrate absorption by roots of tomato. Plant Physiol. 110: 1293-1299.

Lin Y, Cheng CL 1997 A chlorate-resistant mutant defective in the regulation of nitrate reductase gene expression in Arabidopsis defines a new HY locus. Plant Cell 9: 21-35.

Wilkinson JQ, Crawford NM 1993 Identification and characterization of a chlorate-resistant mutant of Arabidopsis thaliana with mutations in both NIA1 and NIA2 nitrate reductase structural genes. Mol. Gen. Genet. 239: 289-297.