A selective role for potassium in the phytotoxicity of thallium

The presence of K-ion prevents inhibition of Plantago maritima seed germination and Asperigillus flavus mycelial growth by Tl-ion. The effect of potassium could not be replaced by Na-ion in either system. Aspergillus was cultured in a medium low in light metal ions (Na+ and K+), and its growth was enhanced quantitatively by addition of Kminus but not Na-ions. Growth without added potassium was inhibited severely by Tl-ions, whereas K-enhanced growth was not. It is suggested that the thallium-potassium interaction is specific involving competition between ions of quite similar charge and radius.