Arsenate reduces copper phytotoxicity in gametophytes of Pteris vittata

The fern Pteris vittata is an arsenic (As) hyperaccumulator and can take up very high concentrations of arsenic from the soil. However, little is known about its response to co-contamination with arsenic and copper (Cu). In this study, we used an in vitro model system of P. vittata gametophytes to investigate the impact of changes in As and Cu status on growth, chlorophyll (chl) concentration, metal accumulation, and subcellular localization. A remarkable inhibition of growth occurred when gametophytes were exposed to concentrations ⩾1.0 mM Na3AsO4 or ⩾0.5 mM CuSO4. chl concentration decreased significantly when gametophytes were exposed to >0.25 mM of CuSO4, but increased steadily with concentration to ⩽2 mM Na3AsO4. Interestingly, the inhibitory effect caused by Cu was reduced in the presence of 0.25 mM Na3AsO4. However, the inhibition caused by exposure to 1.0 mM Na3AsO4 was not alleviated by 0.25 mM CuSO4. Further studies showed that 0.25 mM Na3AsO4 increased cell viability (CV) and chl concentration, while decreasing cell membrane permeability (CMP) of gametophytes with 1.0 mM CuSO4 stress. In contrast, 0.25 mM CuSO4 decreased CV and chl concentration, while increasing CMP when gametophytes were treated with 1.0 mM Na3AsO4. In addition, the subcellular distribution of As and Cu in P. vittata gametophytes differed. As was found primarily in the cytoplasm, while Cu was mainly localized in the cell wall. These results suggest that As can reduce Cu phytotoxicity in the As hyperaccumulator P. vittata, and that this may serve as a biological mechanism for the fern to adapt to soils co-contaminated with As and Cu.