(B-I) Table 4 Genes introduced into plants and the effects of their expression on heavy metal tolerance, accumulation and volatilization (Yang et al., 2005) Gene Product Source mer A Hg(II) reductase Gram-negative bacteria mer A Hg(II) reductase Gram-negative bacteria mer B Organomercurial Gram-negative lyase bacteria APS1 ATP sulfurylase A.
Phytoremediation of mercury and organomercurials in chloroplast transgenic plants: Enhanced root uptake, translocation to shoots and volatilization.
Mercury and organomercurial resistance in rhizobial strains.
Organomercurials have been reported to be 200 times more potent than inorganic mercury.
With organomercurials, the mercury atom still retains a free valency electron, so that salts of such compounds form a monovalent ion.
Organomercurials had been reported to be 200 times more potent than inorganic mercury (mercury bromide) in inducing c-mitosis (Fahmy, F.
Organomercurials are more active as bactericides or fungicides than are the inorganic salts.
The molecular mechanism of bacterial resistance to organomercurials involves the novel enzyme organomercurylyase (Walsh, 1994).
Ten strains were obtained that were resistant to [HgCl.sub.2], of which five were also resistant to organomercurials. The rate of oxidation of NADPH was higher in the presence of [HgCl.sub.2], Hg(I) acetate, thiomersol, PMA, and p-hydroxy mercuribenzoate (Nath et al., 1993).
Even the lowest levels of merBpe expression conferred resistance to organomercurials. The work suggests that native macrophytes, such as trees, shrubs, and grasses, that are engineered to express merBpe may be used to degrade methyl mercury at polluted sites and to sequester Hg(II) for later removal.
Metal Toxicity Cd All forms are toxic and need attention Pb Organic forms are more toxic and easily absorbed by the gastrointestinal tract As Inorganic arsenate [As(+5)] or [As(+3)] are more toxic Hg Hg(II) Organomercurials
mainly methylmercury , biologically magnified Sources: ATSDR (1999), ASTDR (2000), Michalke (2003) Table 2: Food sources of toxic metals.