Selenite enhances arsenate toxicity in Thunbergia alata

Abstract

Environmental context. Arsenic and selenium are two elements ubiquitously distributed in our environment. While selenium is not known to be essential to plants, it is certainly toxic as is arsenic. On the other hand selenium is known to be essential for mammals and an increase in selenium concentration in plants when used as feed or food may be beneficial for mammals in regions of low selenium concentration. The wide distribution of these two elements in the soil might result in elevated co-exposure of plants. So far no interactions of those elements in plants have ever been studied, although this might be mandatory when nutritionists would like to increase the selenium concentrations in crops, which are already challenged by elevated levels of arsenic. Abstract. 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, SeII-PC2 complex and Se-cysteinylserine glutathione, suggested that the increased toxicity symptoms might have been a result of the competition of SeII with AsIII for sulfhydryl groups (crucial for arsenite detoxification in plant cells) as binding partners.