Financial support:We are grateful to SHIGO-CONACYT (2002-060-205) for financial support and for the scholarship to MCBC (2002-020605 Heavy metals are toxic pollutants that have serious adverse effects on human health. They are toxic because can replace other essential metals in pigments or enzymes, disrupting the function of these molecules (Manios et al. 2003). Also because they may cause oxidative stress, especially transition metals as Fe 2+/3+ and Cu +/2+ (Rivetta et al. 1997).The removal of metals from solution using plants offers an attractive alternative, because it is solar driven and can be carried out in situ, minimizing cost and human exposure (McCutcheon and Schnoor, 2003). Plants have developed different mechanisms of tolerance to the metals and to the metal accumulation. Some plants excrete organic acids, as malate and citrate, that act as metal chelators and decrease the rhizospheric pH increasing the bioavailability of metals for phytoextraction (Pivetz, 2001). Organic acids can also inhibit metal uptake because they complex the metal

The ability of in vitro roots cultures of Typha latifolia and Scirpus americanus to remove metals was studied. Roots were cultivated on Murashige-Skoog medium with 15 microg L(-1) Cr 11, 60 microg L(-1) Pb II or 1.8 mg L(-1) Mn II. Adsorbed metal to root surface was removed by washing with 0.042% HNO3. T. latifolia roots were able to uptake 68.8 microg Pb g(-1), 22.1 microg Cr g(-1) and 1680 microg Mn g(-1), while the S. americanus roots removed 148.3 microg Pb g(-1), 40.7 microg Cr g(-1) and 4037 microg Mn g(-1). About 80-90% of Pb and Cr were absorbed in both cultures. On the contrary, the Mn removal was due mainly to an adsorption process (82-86%). In comparison to the T. latifolia cultures, S. americanus cultures were twofold more efficient to remove Pb and Cr, and threefold more efficient to remove Mn. Both plant species capture metals in the following order: Cr >Pb >Mn. This investigation confirms that in vitro roots cultures could be an alternative as a phytoremediation approach for contaminated water with heavy metals.

In vitro roots cultures of Typha latifolia and Scirpus americanus aquatic plants have the capacity to remove Pb (II), Mn (II), and Cr (III) from the culture medium. Both species remove Cr and Pb by an absorption process, while Mn is mainly adsorbed to the root surface. This chapter describes a protocol for the establishment of in vitro roots cultures (nontransformed) from T. latifolia and S. americanus, and the procedure for the uptake analysis of Pb (II), Mn (II), and Cr (III) by roots.