Study on the Tolerance and Detoxification Mechanisms of Lantana camara under the Combined Stress of Cadmium, Lead and Zinc
- XIE Yi-hui, ZHANG Ming-hua, XIONG Rui, LI Ting, PU Yu-lin, XU Xiao-xun, LI Yun, ZHANG Shi-rong, JIA Yong-xia
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Lantana camara is considered to have high tolerance to the Cd, Pb and Zn co-contaminated soil because it can grow normally in Pb-Zn mining area. However, its tolerance and detoxification mechanisms remain unknown. In this study, a pot experiment was conducted to investigate the biomass, relative electrical conductivity, heavy metal content, subcellular distribution and chemical forms of Cd, Pb and Zn in L. camara. The results reveal that:(1) With the increase in the concentrations of heavy metals compound pollution, the biomass of L. camara first increased and then decreased. And it was not until T6[w(Cd) as 60 mg·kg-1, w(Pb) as 800 mg·kg-1, w(Zn) as 1 000 mg·kg-1] treatment that its growth was significantly inhibited; (2) The relative electrical conductivity in roots and leaves of L. camara gradually increased with the rising concentrations of heavy metals, and were significantly higher than that in the control in T3[w(Cd) as 10 mg·kg-1, w(Pb) as 200 mg·kg-1, w(Zn) as 400 mg·kg-1] and T4[w(Cd) as 20 mg·kg-1, w(Pb) as 400 mg·kg-1, w(Zn) as 600 mg·kg-1] treatments, respectively; (3) The Cd concentrations in various parts of L. camara showed a trend of first increasing and then decreasing with the increase of pollution; the Pb and Zn concentrations continued to rise. The content of Cd and Zn in roots of L. camara was higher than that in shoots, and the content of Pb was contrast; (4) Cd and Pb were mainly distributed in the soluble fraction (45.2%-62.5% and 44.2%-66.7%, respectively), followed by the cell wall (29.7%-44.0% and 25.2%-44.1%, respectively), while the concentration of Zn in the soluble fraction (39.2%-52.4%) was similar to that in the cell wall (39.8%-50.4%). A minor part of Cd, Pb and Zn (7.1%-12.2%, 6.0%-13.1% and 4.8%-11.6%, respectively) accumulated in the organelles; (5) Most of Cd, Pb and Zn in the plant organ were mainly in the forms of NaCl and HAc extractable, accounting for 50.7%-73.2%, 47.9%-58.9% and 46.7%-63.2% of total Cd, Pb and Zn, respectively, while the 80% ethanol extractable and deionized water extractable forms accounted for 14.2%-20.8%, 14.6%-28.4% and 19.6%-32.2%, respectively. These results show that L. camara has high tolerance to the Cd, Pb and Zn co-contaminated soil, and the retention of Cd and Zn in the roots, the store of a large amount of heavy metal in cell wall and soluble fraction, and the formation of less toxic chemical forms are important detoxification mechanisms in L. camara.