A chlorate resistant mutant of rice (Oryza sativa L.) with normal nitrate uptake and nitrate reductase activity

Abstract

Most mutants lacking nitrate reductase (NR) activity show a chlorate resistance, but a mutant line M1004, screened based on chlorate resistance, exhibited the same level of NR activity as the wild type Norin 8. Here, we characterized a mutant line M1004 and compared it with a NR deficient mutant line M819 and original cultivar Norin 8. M1004 showed a higher chlorate resistance than M819 at a higher chlorate concentration (1 mM). The same level of NO3/- and ClO3/- uptake as well as NR-mRNA expression was observed in the mutant lines and wild type. NR-mRNA expression was induced in KClO3 solution although the NR activity was inhibited. M1004 exhibited higher a deactivation velocity of NR than the wild type. The results suggested that chlorate resistance in M1004 was caused by the rapid deactivation of NR. This chlorate resistance was transmitted by a single recessive nuclear gene.