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  • Author or Editor: Scott A. Merkle x
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Tissue cultures of pecan [Carya illinoensis (Wangenh.) C. Koch] were initiated from embryo explants collected weekly from 12 weeks post-pollination until fruit maturity. Three cultures derived from immature embryos collected 14 weeks postpollination produced primary somatic embryos within 1 month following transfer from modified woody plant medium (WPM) with 2.0 mgliter−1 2,4-D and 0.25 mg liter−1 BA in the light to hormone-free medium in the dark. Scanning electron microscopy documented the development of secondary embryos, which followed a globular, heartshaped, and torpedo-stage developmental sequence. Chemical names used: (2,4-di-chlorophenoxy) acetic acid (2,4-D), N-(phenylmethyl)-1H-purin-6-amine (BA), and 1H-indole-3-butanoic acid (IBA).

Open Access

The use of plants to stabilize, reduce, or detoxify aquatic and terrestrial pollution is known as phytoremediation. We have employed a molecular genetic approach for the development of potentially phytoremediative species using a bacterial gene for ionic mercury detoxification. One gene of the bacterial mercury resistance operon, merA, codes for mercuric ion reductase. This enzyme catalyzes the reduction of toxic, ionic mercury to volatile, elemental mercury having far lower toxicity. Early attempts to confer Hg++ resistance to plants using the wildtype merA gene were unsuccessful. We hypothesized the highly GC-skewed codon usage was ineffective for efficient plant gene expression, and sequence modification would be necessary to confer merA gene activity and ionic mercury resistance in plants. A directed mutagenesis strategy is being used to develop modified merA gene constructs for transformation and analysis in plants species. Transgenic Arabidopsis and yellow-poplar plants having modified merA codon usage display Hg++-resistance. Arabidopsis plants with modified merA were observed to evolve ≈4 times the quantity of Hg0 from aqueous Hg++ in controlled experiments. In contrast, plants with unaltered merA coding sequences display unstable and inactivated gene expression. Our progress towards further merA modification and transgenic plant development will be reported. Additionally, the theoretical phytoremediative benefits and potential advantages of merA-expressing plant species will be discussed as part of our long-term goals.

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