Authors: Heaton, Andrew¹; Rugh, Clayton²; Wang, Nian-Jie³; Meagher, Richard⁴

Source: Water, Air, and Soil Pollution, Volume 161, Numbers 1-4, February 2005 , pp. 137-155(19)

Publisher: Springer

Abstract:

Plants expressing a modified bacterial mercury reductase, merA, are highly resistant to Hg(II) toxicity as a result of the enzymatically catalyzed electrochemical reduction of Hg(II) to the much less toxic and volatile Hg(0). merA expression may allow plants to manifest a suite of responses to mercury exposure, making them more capable than wild-type plants of interacting with and removing mercury from contaminated soil or water. We have engineered merA-expressing Nicotiana tabacum (tobacco) as a model plant for examining these responses. Mercury resistance was demonstrated by germinating and growing merA tobacco seeds on semi-solid medium spiked with a HgCl₂ concentration acutely toxic to wild-type plants. On similar growth medium, merA plant roots penetrated a highly concentrated, localized Hg(II) zone of HgS (cinnibar) more readily than wild-type roots. In hydroponic medium spiked with HgCl₂, merA plants maintained higher evapotranspiration activity than wild-type plants. The ability of merA Hg(II)-reductive activity to counter typical plant-catalyzed Hg(0) oxidation to Hg(II) was demonstrated by a lower net foliar absorption of atmospheric Hg(0) than wild-type plants. Mercury translocation through merA plants was examined through reciprocally grafted merA and wild-type tobacco grown on HgCl₂-spiked hydroponic medium. Elevated mercury concentrations in wild-type shoots grafted to merA roots suggest the vertical movement of mercury within merA tissues or plants may be facilitated by dynamic balance between native Hg(0) oxidation and MerA-catalyzed Hg(II) reduction. These experiments demonstrate that merA-engineered tobacco plants display an array of tissue-level and whole-plant attributes which should allow for more efficient mercury extraction and processing compared to the wild-type.

Keywords: bioremediation; contamination; Hg; mercury; phytoextraction; phytoremediation; phytovolatilization; transgenic; translocation

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s11270-005-7111-4

Affiliations: 1: Department of Genetics, University of Georgia, Athens, GA, 30602, U.S.A., 2: Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI, 48824, U.S.A., 3: Genaissance Pharmaceuticals, Inc., Five Science Park, New Haven, CT, 06511, U.S.A., 4: Department of Genetics, University of Georgia, Athens, GA, 30602, U.S.A., Email: meagher@uga.edu

Publication date: 2005-02-01

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