Bachelor Thesis

Toxicity of monothioarsenate in rice - influenced by silicon and phosphate

Sonja Pinzer (06/2017-10/2018)

Support: Britta Planer-Friedrich, Carolin Kerl

The uptake of arsenic in rice is a known problem and can be harmful to human health. Rice take up arsenite via the same pathway as silicon and arsenate via phosphate transporters. The uptake and toxicity of monothioarsenates (MTA) had to be clarified in the bachelor thesis. For this reason, growth experiments were carried out with rice plants. The phosphate concentration in the medium was reduced of 50 % and 5 mM silicon was added. The growth inhibition curve showed that arsenite is most toxic to the plants. MTA is less toxic than arsenite but more toxic than arsenate. The effect of silicon on reducing arsenite uptake was not apparent. So is it unclear if MTA is more toxic than arsenate or whether it is a secondary toxicity in the reduction of MTA to arsenite. Normally, arsenate is also reduced to arsenite. However, the reduction of MTA to arsenite is faster than the reduction of arsenite to arsenite. The effect of increased uptake of arsenate or MTA by 50% reduction of phosphate in the medium was evident. A comparison of the IC50- values to the original phosphate-concentration showed that the shoot mass for arsenate decreased by a factor of 7.6 and for MTA by a factor of 6.7. The results, as well as literature, suggest that MTA, like arsenate, is taken up by phosphate transporters.