Changes in chemical forms, subcellular distribution, and thiol compounds involved in Pb accumulation and detoxification in Athyrium wardii (Hook.)

Athyrium wardii is one of the dominant plant species flourishing on the Pb-Zn mine tailings in Sichuan Province, China. A greenhouse pot experiment was conducted to evaluate the chemical forms, subcellular distribution, and thiol compounds in A. wardii under different Pb treatments. The results showed that plants of the mining ecotype (ME) of A. wardii were more tolerant to Pb than those of the non-mining ecotype (NME) in spite of accumulation of higher Pb concentrations. The Pb concentrations in shoots and roots of the ME were 3.2 similar to 8.6 times and 3.0 similar to 24.6 times higher than those of the NME, respectively. The ME was more efficient in Pb uptake than the NME. Moreover, 27.8 similar to 39.0 % of the total Pb in ME was sodium chloride (NaCl) extractable and 38.0 similar to 48.5 % was acetic acid (HAc) extractable, whereas only a minority of total Pb was in ethanol and H2O extractable. In subcellular level, 77.4 similar to 88.8 % of total Pb was stored in the cell walls of ME and 9.0 similar to 18.9 % in soluble fractions. Increasing Pb concentrations enhanced sequestration of Pb into the cell walls and soluble fractions of ME tissues to protect organelles against Pb. Synthesis of non-protein thiols (NP-SH) and phytochelatins (PCs) in roots of ME significantly enhanced in response to Pb stress, and significant increases in glutathione (GSH) were observed in shoots of ME. Higher levels of NP-SH, GSH, and PCs were observed in roots of the ME comparing with NME, especially under high Pb treatments. The results indicated that Pb was localized mainly in cell wall and soluble fraction of ME plants with low biological activity by cell wall deposition and vacuolar compartmentalization, which might be the important adapted Pb detoxification mechanisms of ME.