Quantitative analysis of phosphorus, iron, and arsenic in the inner and outer portions of rice roots: an interaction of arsenic with iron

Two experiments were conducted to observe the effect of arsenic (As; NaAsO2) and additional Fe3+ (Fe3+-EDTA) on phosphorus (P), iron (Fe), and As in inner and outer portions of rice roots (Oryza sativa L. cv. Akitakomachi) grown for 14 days. Measurement of elements was done with PIXE (particle-induced X-ray emission) system. The first experiment contained various rates of As ranging from 0 to as high as 26.8 µM with a constant rate of 10 µM Fe3+, while in the second experiment, the Fe concentrations were varied from 10 to 50 µM with As at 0 and 13.4 µM. The intensity of the reddish coloration in the roots increased with increasing As in the medium. Phosphorus adsorbed by apoplastic Fe and Fe-plaque (outer portion) was not detected, suggesting that P might not have complexed with apoplastic Fe or with Fe-plaque. Iron was mostly concentrated in the outer portion of the roots whereas As was mostly concentrated in the inner portion. High-Fe3+ in the medium caused a decrease in P and As concentrations in the inner portion of the roots.