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Cadmium is a heavy metal, which, even in low concentrations, can be highly
toxic to the growth and development of both plants and animals. Plant species
vary extensively in their tolerance to excess cadmium in a growth medium and
very few cadmium-tolerant species have been identified. In this study,
tumbleweed plants (Salsola kali) grown in an agar-based medium with 20
mg l-1 of Cd(II) did not show phytotoxicity, and their roots had the most
biomass (4.5 mg) (P<0.05) compared to the control plants (2.7 mg) as well as
other treated plants. These plants accumulated 2,696, 2,075, and 2,016 mg of
Cd per kg of dry roots, stems, and leaves, respectively. The results suggest
that there is no restricted cadmium movement in tumbleweed plants. In addition,
the amount of Cd found in the dry leaf tissue suggests that tumbleweed could be
considered as potential cadmium hyperaccumulating species. X-ray absorption
spectroscopy studies demonstrated that in roots, Cd was bound to oxygen while
in stems and leaves the metal was attached to oxygen and sulfur groups. This
might imply that some small organic acids are responsible for Cd transport from
roots to stems and leaves. In addition, it might be possible that the plant
synthesizes phytochelatins in the stems, later coordinating the absorbed
cadmium for transport and storage in cell structures. Thus, it is possible that
in the leaves, Cd either exists as a Cd-phytochelatin complex or bound to cell
wall structures. Current studies are being performed in order to elucidate the
proposed hypothesis.
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