Selenite enhances arsenate toxicity in Thunbergia alata

The suspected antagonism between selenite and arsenite in various mammalian species gave reason to investigate the effect of selenite on arsenate toxicity in higher plants using Thunbergia alata as a model plant. Here, we present a study involving (1) toxicity tests, (2) uptake and translocation experiments as well as (3) selenium-sulfur-arsenic speciation analysis by HPLC-ESMS-ICP-MS (oxygen) of selected plant tissues. The EC50 (effective concentration that inhibits growth by 50%) values, as a result of the toxicity studies, showed that selenite co-exposure enhances arsenate toxicity. The detection of two selenium species, Se-II-PC2 complex and Se-cysteinylserine glutathione, suggested that the increased toxicity symptoms might have been a result of the competition of Se-II with As-III for sulfhydryl groups (crucial for arsenite detoxification in plant cells) as binding partners.