|Budget Amount *help
¥2,600,000 (Direct Cost : ¥2,600,000)
Fiscal Year 1991 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1990 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1989 : ¥1,700,000 (Direct Cost : ¥1,700,000)
1) To obtain mutants deficient in nitrate reductase (NR) in rice, screening for chlorate resistant lines maintained at the Institute to Radiation Breeding, NIAR, Japan. Of 437 lines tested, four chlorate resistant lines (M819, M821, M1004 and M1009) were selected. Differences in chlorate sensitivity were also observed among the four selected lines. The levels of in vitro NR activity of seedlings in M819 and M821 were below 30% of that of their parent. Norin 8, M819 and M821 were identified as low NR activity lines. NR activity in M1009 was about 80% of that of Norin 8. However, NR activity in M1004 was the same level as that in Nor-in 8. Seedlings of four selected lines took up nitrate to the same extent or a higher than Norin 8.
2) Biochemical and genetical characterization of a rice nitrate reductase (NR) -deficient mutant, M819, which had been isolated as a chlorate resistant mutant, was carried out. In M819, leaf NADH-NR activity was about 10% of that in the wild type cultivar, Nori
n 8, while NADPH-NR activity was higher than that in the wild type. In M819, FNNH_2-NR and MV-NR activities were also 10% of the wild type. BPB-NR activity in the mutant was higher than that in the wild type. Xanthine dehydrogenase activity was revealed to be present in both M819 and the wild type. These results suggest that the mutant line M819 lacks the functional heme domain of NADH-NR polypeptide due to a point mutation or a small delection with the coding region of the structural gene. Chlorate resistance in M819 was transmitted by a single recessive nuclear gene.
3) Biochemical characterization of two rice mutants, M819 and NR827, affecting NR was carried out. Both mutants had XDH and fully functional Mo-Co, indicating that both were not Mo-Co mutants. M819 lacked NADH-NR and had low NADH-CcR value. M819 had same Nir level as the wild type cultivar. On the other hand, in NR827, not only NADH-NR and NADH-CcR but also NiR activities were around 70-80% of those of the wild type cultivar. The level of NR activity of NR827 was intermediate between normal plants and NR-deficient mutants. In NR827, decrease in nitrate concentration in the tissue was also observed, but net nitrate uptake was as same as the wild type cultivar. From these results, it is concluded that M819 was -defective in NADH-NR, but the biochemical characteristics of NR827 NR is unclear. It might be possible that NR827 was a mutant totally impaired in the nitrate assimilation. Less