Abstract
A rice mutant hypersensitive to chlorate (an analog ion for nitrate), M605, was isolated from the mutant lines derived from a japonica cultivar, Norin 8. In this experiment, three biochemical steps of nitrate assimilation, i.e. nitrate uptake, nitrate reduction and nitrite reduction, were ana-lyzed using M605, Norin 8 and a chlorate hypersensitive indica cultivar, Leuang Tawng. Uptake ability of monova-lent anions including nitrate in M605 and Leuang Tawng was lower than that of Norin 8 except for chlorate uptake in M605. Chlorate uptake from a 200 /1 M potassium chlo-rate solution in M605 was 1.2 fold that in Norin 8. In both seedlings and roots of M605, activities of NADH-NR, NADPH-NR and NiR were similar to those of Norin 8. These results indicate that chlorate hypersensitivity in M605 may be due to the increased level of chlorate uptake. Genetic study showed that chlorate hypersensitivity in M605 was transmitted by polygenic factors. On the other hand, activities of leaf NRs and NiR of Leuang Tawng were twice to three times higher than those of Norin 8. There was no difference in the activities of root NRs and NiR between Leuang Tawng and Norin 8. It was suggested that the chlorate hypersensitivity in Leuang Tawng may be due to the higher activities of leaf NRs and NiR.
