Abstract
Nitrate uptake ability from low-concentration nitrate solution was evaluated based on Michaelis-Menten kinetics in rice. In 16 cultivars, including eight japonica and eight indica, apparent Km (Michaelis constant) and apparent Vmax (maximum uptake rate) ranged from 75.7 to 130.3 μM and from 4.30 to 7.17 μmol/g fresh weight/h, respectively. There was no difference in both apparent Km and apparent Vmax between japonica and indica, suggesting that there was no intraspecific difference in the gene encoding nitrate uptake carrier. However, small differences in both apparent Km and apparent Vmax were found within each subspecies. Of four mutants related to nitrate assimilation, M605, a chlorate hypersensitive mutant, showed remarkably higher apparent Km than the original cultivar, Norin 8. This fact suggests that the nitrate uptake carrier can be altered by mutation.
