Reduced Level of NADH-dependent Nitrate Reductase Activity in Rice Mutant M819 Due to Deletion of a Valine Residue in Heme Domain.

Abstract

It was previously reported that the rice nitrate reductase (NR)-deficient mutant M819 (wild type: cv. Norin 8) Iacks the functional heme domain of NADH-NR polypeptide possibly due to a point mutation or small deletion. In this paper we were able to locate the mutation in the NR apoenzyme gene. Northern blot analysis using a rice NADH-NR genomic clone as a probe showed that the size of NR mRNA of M819 was the same as that of the wild type, suggesting that the mutation did not involve a large deletion or insertion in the NADH-NR coding sequence. The DNA fragment containing the coding region of NADH-NR heme domain was amplified by PCR from M 819 and Norin 8. The alignment of nucleotide sequences of the domain revealed that 3 nucleotides (GTC) encoding one valine residue (Val-561 or Val-562) were deleted in M819. Thus, it was demonstrated that there was a point mutation in the coding region of NADH-NR heme dornain in the mutant M819.