Arsenic mobilization in rice (Oryza sativa) and its accumulation in the grains

Abstract

Flooded rice (Oryza sativa L.) may contain high arsenic (As) concentrations compared to other grain crops. For the development of measures to reduce the As concentration of rice grains, knowledge about the mobility of As within the rice plant is required. Therefore, to investigate the mobilization of As within the plant, rice was grown in nutrient solution and exposed to As either before flowering, after flowering, or continuously until maturity. Furthermore, rice was grown in four soils under greenhouse and field conditions and the time course of As accumulation in grains during the grain-filling period was investigated. When grown in nutrient solution, As removal at flowering did not reduce As concentrations in polished rice compared to plants supplied with As continuously or after flowering. Plants that received As only after flowering had the same As concentrations in shoot and bran as plants receiving As only before flowering. However, continuous As supply resulted in doubling of As concentrations in both plant parts. In contrast to grain and shoot, the As concentration in the root decreased after As removal compared to the treatments receiving As only after flowering or continuously. The observations indicate that As was mobilized from root or shoot to the grain and that it was accumulated in the grain, although it was not available in nutrient solution during the grain-filling period. In soil experiments, the 1000-grain weight increased up to 2 weeks before harvest in the field as well as in the greenhouse. The As concentration in rice grain was constant during the whole grain-filling period. It was at a similar level under field and greenhouse conditions, and its variation among soils was in the same order indicating that soil was the decisive factor for As concentration in grains. Our results suggest that temporary cultural measures during the cultivation period, for example drainage, might be ineffective because of the mobilization capacity within the rice plant. Moreover, harvest before final maturity of grains would not reduce the As concentration since it remained constant during the grain-filling period.

Irrigation Practices on Rice Crop Production in Arsenic‐Rich Paddy Soil

“…Similar results are reported by Marin et al (1993), Rahman et al (2004), and Bogdan and Schenk (2012). Other studies (Marin et al, 1993; Abedin et al, 2002a, 2002b; Meharg and Jardine, 2003; Rahman et al, 2007a, 2007b; Chou et al, 2014) pointed out that the partitioning of As within rice plants was in the order: roots > leaves > shoots regardless of the rice variety and cultivation method used in the experiments.…”

“…In their experimental results, Bogdan and Schenk (2012) showed that, with As‐rich irrigation water, flooded paddies provided abundant sources of As to the root zone, contributing to the higher As concentration in the roots. The present study obtained similar results, with roots, leaf blades, and shoots accumulating substantial As in both cropping seasons, particularly roots (Fig.…”

Distribution and Accumulation of Arsenic in Rice Plants Grown in Arsenic‐Rich Agricultural Soil

“…There are four types of As species found in paddy soils, arsenite (As III ), arsenate (As V ), dimethylarsenate (DMA), and monomethylarsenate (MMA) (Bogdan and Schenk, 2012). Inorganic As is generally more toxic than methylated As compounds (Schoof et al, 1999).…”

Qualidade e segurança do arroz brasileiro: avaliação de arsênio total e inorgânico em diferentes locais, cultivares e sistemas de cultivo

“…Após entrar nas células da raíz, o AsV é convertido em AsIII e pode sofrer efluxo para o meio ou ser transportado para o xilema por meio de canais aquaporinas Lsi2. Além disso, a planta possui alguns sistemas de detoxificação nas raízes como a conversão de AsIII em AsV, a complexação/sequestro de AsIII por fitoquelatinas (PCs), e transporte/armazenamento nos vacúolos das células da raíz (RAAB et al, 2005;MA et al, 2008;ZHAO et al, 2009;BOGDAN;SCHENK, 2011;BATISTA et al, 2014).…”