Fe(II) and Fe(III) Uptake Efficacies of Rice (Oryza sativa).

Paddy rice is grown under submerging condition and the change in the redox status of paddy soil results in the temporal and spatial variations in the Fe(II)/Fe(III) distribution in the soil. Although rice root can uptake both Fe(II) (the Strategy I) and Fe(III) (the Strategy III) from the rhizosphere soil, it is unclear how rice root regulates the uptake of Fe while the Fe(II)/Fe(III) distribution changes with growing time. Thus, the aim of this study was to investigate the uptake efficacies of rice root for Fe(II) and Fe(III). Rice plants were grown in hydroponic solutions with different Fe(II) and Fe(III) concentrations and the uptake amounts of Fe(II) and Fe(III) by rice root were determined. Increasing Fe(II) or Fe(III) concentration resulted in the decrease in the solution pH and the increase in Fe uptake by rice. With a higher Fe(II) concentration, the amount of Fe hydroxide precipitate on rice root increased. The formation of Fe(III) hydroxide is attributed to the release of oxygen from rice root. Thus, the radial oxygen loss from rice root plays a key role in regulating the availability of Fe(II) in the rice rhizosphere.