Use of phosphorus to alleviate stress induced by cadmium and zinc in two submerged macrophytes
AbstractThe potential mechanism by which P antagonizes the toxicity of Zn and Cd was investigated in Elodea nuttallii and Hydrilla verticillata to understand the interactions between P, Cd and Zn pollutants. The two
submerged macrophytes were treated with a combination of Cd (0.25 mg L-1) and Zn (1.0 mg L-1) and various concentrations of P (0, 0.05 and 5 mg L-1) for different exposure times (0.5, 1, 2, 4 and 7 days).
The toxic effects and oxidative stress caused by the Cd and Zn resulted in a reduction of the total chlorophyll (chlorophyll a and b) and an increase in the content of glutathione (GSH). The activity of
catalase (CAT) and the contents of malondialdehyde (MDA) both increased in the 1st day, and then reduced during the following 6 days. However, the activity of guaiacol peroxidase (POD) and the
contents of soluble protein both decreased in the first day then increased from the 2nd to 7th days. Each index in the plants treated with Cd and Zn containing P showed similar changing trends to those treated with only Cd and Zn during the 7 days. However, different indices had different response times. At the best response time in each index, the result showed that using P can protect plants from the toxicity and oxidative stress caused by Cd and Zn, which suggested that P can produce an antagonistic response with Cd and Zn to mitigate the oxidative stress to plants. Also, these results suggested that Cd and Zn exerted their toxic effects on the growth of E. nuttallii and H. verticillata, at least in part, by the induction of oxidative stress and inhibition of photosynthesis. Through comparing the response of the two plants to oxidative stress caused by Cd and Zn, it was found that E. nuttallii was more sensitive than H. verticillata. E. nuttallii can be regarded as an indicative plant for Cd and Zn polluted waters.