Foliar application of silica nanoparticles alleviates arsenic accumulation in rice grain: co-localization of silicon and arsenic in nodes

Foliar application of silica nanoparticles (NPs) to plants can improve stress tolerance and enhance plant growth; however, it remains poorly understood how it regulates arsenic (As) uptake and transport to rice grain when rice is exposed to arsenic stress. In this study, rice plants under arsenite stress during the whole growth period were foliarly applied with silica NPs for one week at the jointing and flowering stages, respectively. Results showed that the arsenic concentration in grain was significantly reduced by 7.11-15.1% in the silicon (Si) amended treatments, though silicon application could not decrease arsenic accumulation in the whole plant or its root-to-shoot translocation factor. Silicon application substantially increased the arsenic concentrations in nodes, particularly those in node I by 101-193%, restricting arsenic transport to leaves, husks and grains. Gene expression of Si/As related transporters in the roots and nodes, including OsLsi6, OsLsi2, OsLsi3 and OsABCC1, showed no significant difference between the control and Si amended treatments. Bioimaging of the multi-elemental distribution in node I by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) revealed that arsenic was co-localized with sulfur in the vascular system, while a layer of arsenic was formed at the peripheral tissues, which strongly co-localized with Si. Heavy Si deposition was also observed in the vascular system, likely contributing to arsenic immobilization in the nodes. Our findings provide new insights into the mechanisms of arsenic uptake and transport in rice plants regulated by foliar application of silica NPs, which are useful for application in arsenic-contaminated paddy fields.

Automated summary

The foliar application of silica nanoparticles to rice plants can reduce arsenic concentration in grains and restrict arsenic transport to leaves, husks, and grains. While silicon application does not decrease arsenic accumulation in the whole plant, it alters the distribution of arsenic in the plant.