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

Most mutants lacking nitrate reductase (NR) activity show a chlorate resist ance, but a mutant line M1004, screened based on chlorate resistance, exhib ited the same level of NR activity as the wild type Norin 8, Here, we chara cterized a mutant line M1004 and compared it with a NR deficient mutant lin e M819 and original cultivar Norin 8, M1004 showed a higher chlorate resist ance 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 mu tant lines and wild type, NR-mRNA expression was induced in KClO3 solution although the NR activity was inhibited, M1004 exhibited higher a deactivati on velocity of NR than the wild type, The results suggested that chlorate r esistance in M1004 was caused by the rapid deactivation of NR. This chlorat e resistance was transmitted by a single recessive nuclear gene.