The role of small molecules in restricting rice accumulation of dimethylarsinic acid

Abstract

Dimethylarsinic acid (DMA), an organic arsenic compound found in rice grain, is a causal agent of straighthead disorder, which can decimate yields. To minimize rice accumulation of DMA, we tested 9 molecules for antagonistic effects with DMA. We also tested whether the source of nitrogen is able to affect DMA uptake, as DMA is a weak acid and different nitrogen sources have differing effects on rhizospheric pH. We grew rice (Oryza sativa L. cv. Lemont) hydroponically to maturity in two different experiments. First, 9 potential competitors (boric acid, calcium, glycerol, glycine, lactic acid, phosphoric acid, serine, silicic acid, and urea) were included in the hydroponic solution at a molar ratio ≥ 100:1 competitor:DMA. Second, rice receiving 5 μM DMA was grown under ammonium, nitrate, or a 1:1 mix of ammonium and nitrate. Yield metrics and plant elemental concentrations were measured after harvest. Of the potential competitors, only silicic acid was able to alleviate straighthead disorder and no competitors were able to reduce grain As by ≥30%. Under differing nitrogen sources, nitrate decreased plant concentrations of As relative to ammonium, but not in the grain. While Si can alleviate DMA uptake, there remains uncertainty in how most DMA enters the plant.