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12 Transgenic Approaches to Enhance Phytoremediation of Heavy Metal-Polluted Soils 261

promoting mobilization of metals in soils. Efforts should thus be devoted to assess
the effect that modifications for enhanced secretion of metal-complexing root
exudates, ideally combined with implementation of the cognate metal-complex
transport mechanism, would have on phytoextraction of soil metals. Conversion
of immobile metals to their bioavailable forms in soils is largely dependent on the
activity of soil microflora. Thus, modification of bacteria and fungi for secretion of
protons and metal ligands can be also taken into account.
Genetically modified plants may endue remediation of heavy metal contamina-
tion with obvious benefits, yet some would question their techno-economic per-
spective and environmental safety. The best way to determine the true
phytoremediation potential of genetically modified plants is by conducting field
trials (Ban ˜uelos et al. 2005, 2007; Van Huysen et al. 2004), which must be also
designed to assess risks.

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