Hydroxyiminodisuccinic acid (HIDS): A Novel Biodegradable

24 The 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 neutral or alkaline pH in oxic condition. Chelating ligands produce soluble ‘Fe-ligand complex’ 29 which assist Fe uptake in plants. The biodegradable chelating ligand hydroxyiminodisuccinic 30 acid (HIDS) was more efficient then those of ethylenediaminetetraacetic acid (EDTA), 31 ethylenediaminedisuccinic acid (EDDS), and iminodisuccinic acid (IDS) in the increase of Fe 32 uptake and growth of rice seedling. A total of 79±20, 87±6, 116±15, and 63±18 mg dry biomass 33 of rice seedlings were produced with the addition of 0.5 mM of EDDS, EDTA, HIDS, and IDS 34 in the nutrient solution, respectively. The Fe concentrations in rice tissues were 117±15, 82±8, 35 167±25, and 118±22 μmol g dry weights when 0.25 mM of EDDS, EDTA, HIDS, and IDS 36 were added to the nutrient solution, respectively. Most of the Fe accumulated in rice tissues was 37 stored in roots after the addition of chelating ligands in the solution. The results indicate that the 38 HIDS would be a potential alternative to environmentally persistent EDTA for the increase of Fe 39 uptake and plant growth. The HIDS also increased As uptake in rice root though its translocation 40 from root to shoot was not augmented. This study reports HIDS for the first time as a promising 41 chelating ligand for the enhancement of Fe bioavailability and As phytoextraction. 42