Rice is currently one of the most important foods in the world (especially Southeast Asia), but arsenic (As) contamination of rice is one of the main pollution pathways into the human food chain. Arsenic contamination of rice not only affects its yield and quality, but also threatens human health. There is an urgent requirement to understand the mechanisms of As tolerance and uptake by rice. In roots, oxygen is required for respiration in order to provide sufficient energy for growth, maintenance and nutrient uptake. However, significant amounts of oxygen loss through the root apex, (with up to 30%-40% of the oxygen being supplied via the root aerenchyma) to the soil is a process termed as radial oxygen loss (ROL). ROL occurs in the aerated rhizosphere of plant roots growing in waterlogged soil and results in significant changes in soil chemistry within the rhizosphere. Previous studies have shown that ROL was related to As accumulation and speciation, with total ROL from the root system being positively correlated with metal tolerance and negatively correlated with total and inorganic As in rice grains from 20 different genotypes. This paper assesses As tolerance and accumulation in three genotypes namely, CNT 87059-3, IAPAR9 and Yuxiangyouzhan; each possessing different ROL under different As treatments.
Experimental results showed that: (1) Root length was significantly different between the three genotypes (<0.05), (2) Yuxiangyouzhan had the highest ROL and the greatest tolerance index (0.71) when exposed to 2 mg/L As, (3) the tolerance indices of the three genotypes decreased with increasing As concentration, (4) shoot and root biomass were significantly different between the three genotypes and treatments (P < 0.05) and (5) arsenic concentrations in roots were significantly different between the three genotypes (P < 0.01) (IAPAR with higher ROL, 336 mg/kg, CNT 87059-3 with lower ROL, 660 mg/kg), but not significantly different in shoots (P > 0.05). It is concluded that ROL is significantly correlated with As tolerance and accumulation. Rice cultivars with higher ROL have greater As tolerance and lower accumulation. Therefore, ROL can be a potential selection criterion for selecting suitable rice cultivars to grow in areas of high As contamination. This study provides significant findings regarding As tolerance in rice related to ROL and provides potential strategies to mitigate the health risk posed by As contamination. However, the mechanism for As tolerance and accumulation, as well as field application for mitigating As accumulation in rice grains needs further investigation.