Arsenate uptake by Pi transport system of an arsenate-resistant mutant, AR3, of Chlamydomonas

Abstract

It is known that arsenate is taken up by the cells via Pi transport systems. In a green alga Chlamydomonas, arsenate was a competitive inhibitor of Pi transport systems, and the toxicity of arsenate disappeared in the presence of higher concentration of Pi. An arsenate-resistant mutant, AR3, which was generated by the random insertional mutagenesis, showed lower arsenic- and higher P-contents in the cells in the presence of arsenate than those of the wild type. The kinetics of Pi uptake demonstrated that AR3 had a high activity of a high-affinity Pi transport system even in the presence of 1mM Pi, where the system was suppressed in the wild type. The higher intracellular P content in AR3 might be due to one of the high-affinity Pi transporters. On the other hand, the kinetics of arsenate uptake indicated that the mutant had a high activity of a high-affinity arsenate transport system, which was suppressed rapidly after the incorporation in of arsenate into the cell. These results suggest that the arsenate resistance in AR3 is attributed to the high P content maintained by the activated Pi transport system and to the specific suppression of arsenate uptake via the Pi transport system.