Pinpointing where plants store arsenic
Ladder ferns pick up arsenic—and make it more toxic in some surprising places.
Plants such as the fern Pteris vittata can take up toxic substances and store them, a quality that makes them attractive for cleaning up polluted sites. New X-ray images, shown here and published on ES&T Research ASAP (DOI: 10.1021/es052559a), reveal how this particular fern sequesters arsenic.
The images show that the fern transforms arsenate (AsO43–) into the even more toxic arsenite (H2AsO3–) in its leaves, not in its roots as previously thought. It also tucks the arsenite away inside its cell vacuoles; this may be a coping mechanism against arsenite’s toxicity. Exactly how the plant transforms the arsenic remains unclear, but the researchers who captured the new pictures say that their technique (which uses synchrotron radiation at the Stanford Linear Accelerator Center) may be the most precise yet in showing where and in what forms the fern stores arsenic.
The team mapped live plants and single-cell-thick gametophytes by hitting them with microscopic X-ray beams at different energy levels. Different arsenic forms “show up” at different energies, providing “a whole picture,” says Graham George of the University of Saskatchewan (Canada). “When you do it this way, features kind of pop out of the map,” says Ingrid Pickering, George’s colleague and the first author of the work. Only one high-energy level X ray would have missed the nuances, she adds.
“The results are far-reaching and are of interest from the standpoint of fundamental knowledge as well as for the use of plants to remediate sites contaminated with arsenate,” says Bob Buchanan, a molecular plant biologist at the University of California, Berkeley. Deciphering the fern’s behavior could be useful in genetically modifying plants for such cleanup purposes, the team notes.
