Effects of different inhibitors such as malonic acid, Na3PO4 and HgCl2 on uptake of different forms of antimony in rice plant

Abstract

Antimony is an analogue of arsenic (As), but its uptake mechanisms are not as well understood as As. Antimonite [Sb(III)] probably enters into plant roots via aquaporins but antimonate [Sb(V)] not through the phosphate [P(V)] uptake system as with arsenate [As(V)]. However, previous studies observed a dose−dependent interaction between As(V) and P(V) in some plants. This study was conducted mainly to identify that 1) whether the uptake of Sb(III) by plants will be via aquaporin channels; 2) whether the interaction effects between Sb(V) and P(V) might be dose−dependent; 3) whether the uptake of Sb(III) or Sb(V) is at the cost of energy. Two hydroponic culture systems were set up using a rice plant (YeXiangYou No.3) to investigate the effects of different chemicals on the uptake of Sb in the rice plants subjected to Sb(III) and Sb(V). These chemicals included malonic acid (C3H4O4), Na3PO4 [P(V)] and HgCl2. Sb was mainly sequestrated in the roots of the rice plants, suggesting a low transport capacity of Sb from roots to shoots. The plants took up Sb more easily under Sb(III) exposure than under Sb(V) exposure. 10 mg L−1 Sb(III) increased the Sb concentration in the bleeding sap rather than the weight of the bleeding sap; but the situation reversed when rice plants were exposed to Sb(V), suggesting different transport mechanisms of Sb from roots to shoots between Sb(III) and Sb(V). The addition of C3H4O4 generally reduced the Sb concentrations in the shoots and roots subjected to Sb(V), suggesting the uptake of Sb(V) to be energy dependent. The addition of Na3PO4 also significantly reduced the concentrations of Sb in the shoots and roots when plants were exposed to Sb(V). Interestingly, the addition of HgCl2 significantly reduced the concentrations of Sb in the shoots and roots when rice plants were exposed to both Sb(III) or Sb(V), possibly implying that uptake of Sb(III) might be via aquaporins and Cl− played a role in affecting the uptake of Sb(V). The results of this study suggested that uptake of Sb(III) is via aquaporins, and Cl− as well as PO43− may compete with Sb(V) for uptake pathway.