A CHLORATE-HYPERSENSITIVE, HIGH CHLORATE UPTAKE MUTANT IN RICE (ORYZA-SATIVA L)

A rice mutant hypersensitive to chlorate (an analog ion for nitrate), M605, was isolated from the mutant lines derived from a japonica culti var, Norin 8, In this experiment, three biochemical steps of nitrate a ssimilation, i.e. nitrate uptake, nitrate reduction and nitrite reduct ion, were analyzed using M605, Norin 8 and a chlorate hypersensitive i ndica cultivar, Leuang Tawng. Uptake ability of monovalent anions incl uding nitrate in M605 and Leuang Tawng was lower than that of Norin 8 except for chlorate uptake in M605, Chlorate uptake from a 200 mu M po tassium chlorate solution in M605 was 1.2 fold that in Norin 8. In bot h seedlings and roots of M605, activities of NADH-NR, NADPH-NR and NiR were similar to those of Norin 8. These results indicate that chlorat e hypersensitivity in M605 may be due to the increased level of chlora te uptake, Genetic study showed that chlorate hypersensitivity in M605 was transmitted by polygenic factors. On the other hand, activities o f leaf NRs and NiR of Leuang Tawng were twice to three times higher th an 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 t he chlorate hypersensitivity in Leuang Tawng may be due to the higher activities of leaf NRs and NiR.