Effects of nanoscale silica sol foliar application on arsenic uptake, distribution and oxidative damage defense in rice (Oryza sativa L.) under arsenic stress

It has been widely reported that silicon (Si) can enhance rice resistance and/or tolerance to arsenic (As) toxicity; however, there is very little evidence suggesting that nanoscale silica foliar applications can decrease As accumulation in rice grains grown in As-contaminated environments. This study is aimed at investigating the mechanism of nanoscale silica sol foliar applications on the alleviation of As toxicity and reduction of its accumulation in rice. Pot, field and hydroponics experiments were conducted to study the effects of nanoscale silica sol foliar application on biomass and As accumulation in rice plants. The electrolyte leakage (EL), malondialdehyde (MDA) content, and activity of antioxidant enzymes were also examined in rice, grown in a 50 or 100 mM As contained nutrition, with or without 5 mM nanoscale silica sol foliar pretreatment. The results showed that nanoscale silica sol foliar application significantly increased the grain yields, while decreasing the As concentration of brown rice in pot and field experiments, induced more As combined on the cell walls of shoots, decreased EL and MDA content in roots and increased the activity of antioxidant enzymes, including superoxide dismutase (SOD), preoxidase (POD), catalase (CAT), and asorbate peroxidase (APX) in the roots of rice seedlings grown in the As contained nutrition. These results indicated that nanoscale silica sol foliar application was effective in the alleviation of As toxicity and accumulation in rice. These were mainly attributed to the enhanced antioxidant defense capacity resulting from the Si treatments. The mechanism of nanoscale silica foliar application to alleviate the toxicity and accumulation of As in grains of rice may also be related to the probable As sequestration in the shoot cell walls.