24The influence of biodegradable chelating ligands on arsenic and iron uptake by hydroponically 25 grown rice seedlings (Oryza sativa L.) was investigated. Even though the growth solution 26 contained sufficient Fe, the growth of rice seedlings gradually decreased up to 76% with the 27 increase of pH of the solution from 7 to 11. Iron forms insoluble ferric hydroxide complexes at 28

(As(V)) transport into plant cells has been well studied. A study on rice (Oryza sativa L.) showed that arsenite is transported across the plasma membrane via glycerol transporting channels. Previous studies reported that the dimethylarsinic acid (DMAA) and monomethylarsonic acid (MMAA) uptake in duckweed (Spirodela polyrhiza L.) differed from that of As(V), and was unaffected by phosphate (H 2 PO 4 ). This article reports the transport mechanisms of DMAA and MMAA in rice roots. Linear regression analysis showed that the DMAA and MMAA uptake in rice roots increased significantly (p ≤ 0.0002 and ≤ 0.0001 for DMAA and MMAA, respectively) with the increase of exposure time. Concentration-dependent influx of DMAA and MMAA showed that the uptake data were well described by MichaelisMenten kinetics. The MMAA influx was higher than that of DMAA. The DMAA and MMAA uptake in rice roots were decreased significantly (p ≤ 0.0001 and ≤ 0.0077 for DMAA and MMAA, respectively) with the increase of glycerol concentration indicating that DMAA and MMAA were transported into rice roots using the same mechanisms of glycerol. Glycerol is transported into plant cells by aquaporins, and DMAA and MMAA are transported in a dosedependent manner of glycerol which reveals that DMAA and MMAA are transported into rice roots through glycerol transporting channels. The DMAA and MMAA concentration in the solution did not affect the inhibition of their uptake rate by glycerol.

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22This study was conducted to investigate the effect of external iron status and arsenic indicated that iron uptake in shoots was neither affected by additional iron nor by arsenic species. 36Compared to the control, chelating ligands increased iron uptake in shoots of rice seedlings 37 significantly (p < 0.05). Regardless of additional iron and arsenic species, iron uptake in rice 38 shoots did not differed among EDTA, EDDS, and HIDS treatments.