Silicon Decreases Dimethylarsinic Acid Concentration in Rice Grain and Mitigates Straighthead Disorder

Abstract

While root Si transporters play a role in the uptake of arsenite and organic As species dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) in rice ( Oryza sativa L.), the impact of Si addition on the accumulation of DMA and MMA in reproductive tissues has not been directly evaluated, particularly in isolation from inorganic As species. Furthermore, DMA and MMA are suspected causal agents of straighthead disorder. We performed a hydroponic study to disentangle the impact of Si on accumulation of DMA and MMA in rice grain. At 5 μM, MMA was toxic to rice, regardless of Si addition, although Si significantly decreased root MMA concentrations. Plants dosed with 5 μM DMA grew well vegetatively but exhibited straighthead disorder at the lowest Si dose, and this DMA-induced yield loss reversed with increasing solution Si. Increasing Si also significantly decreased DMA concentrations in roots, straw, husk, and grain, particularly in mature plants. Si restricted grain DMA through competition for root uptake and downregulation of root Si transporters particularly at later stages of growth when Si uptake was greatest. Our finding that DMA causes straighthead disorder under low Si availability but not under high Si availability suggests Si as a straighthead management strategy.

Arsenic concentrations and speciation in Australian and imported rice and commercial rice products

“…Recent research, however, has shown that an increase in DMA uptake occurs on expression of the OsNIP2:1 aquaporin channel (Zhao et al 2013). As well, in hydroponic experiments, an increase in Si media concentrations decreased DMA concentrations in rice plants (Limmer et al 2018). Thus, DMA uptake mechanisms and the role of Si in these mechanisms require further investigation.…”

“…Unlike for As III , Si transporters are unlikely to be responsible for the uptake of DMA, although Li et al (2009) have shown that the root silicic acid transporter OsNIP2:1 may play a role in DMA uptake. As well, Si has been shown to substantially decrease the uptake of DMA by some rice cultivars in hydroponic experiments (Limmer et al 2018). The role of Si transporters in DMA uptake remains unclear.…”

“…Other As species such as dimethylarsinic acid (DMA), monomethylarsonate (MA) and tetramethylarsonium ions (TETRA) have also been reported in rice (Batista et al 2011;Hansen et al 2011;Hua et al 2011), and are probably the result of the reduction and methylation of inorganic As in rhizosphere soils under anaerobic growth conditions (Lomax et al 2012 ;Zhao et al 2013;Zecchin et al 2017b) as genes responsible for As methylation have yet to be found in rice (Ye et al 2012). DMA is thought to be the cause of straighthead in rice (Limmer et al 2018). Straighthead is a physiological disorder in which grains do not fill and the panicle remains erect, resulting in decreased grain yields.…”

Si and Water Management Drives Changes in Fe and Mn Pools that Affect As Cycling and Uptake in Rice

“…First, regardless of whether a Si amendment increases porewater As relative to Control (Figure 1A), its ability to also provide sufficient Si to porewater after competitive desorption of arsenite in bulk soil ( Figure 1B) allows for Si to compete with As for root-uptake via the highly-efficient Si/As root transport pathway [57,58] in rice. Second, higher exogenous Si leads to decreased gene expression of Si root transporters [59][60][61], thus restricting the potential pathways (i.e., Si/As root transporters) for As uptake. Third, higher exogenous Si promotes ferrihydrite-rich plaque (Figure 3 and ref.…”

Soil attribute regulates assimilation of roxarsone metabolites by rice (Oryza sativa L.)

“…Regression models for arsenic in rice plant (Y) and soil property (variable) in soils fertilized with two chicken manures without or bearing roxarsone metabolites (CM and ROXCM), respectively. It is noticeable that the increased DMA in brown rice caused by ROXCM application might not pose serious arsenic health impact to human due to its low toxicity to organisms (Zhao et al, 2010), however, it might lead to "straighthead" symptom, a physical disorder linked with arsenic (DMA in particular) in rice plant (Agrama and Yan, 2009;Limmer et al, 2018;Rahman et al, 2008;Yan et al, 2005).…”