One benefit of the method is that it is heavily regulated by the government, while each year
dozens of new plant varieties produced through traditional methods are marketed without any
scientific review or special labeling. Genetic splicing is a chemical process that involves using restriction enzymes to cut the DNA of a gene to add base pairs. Each restriction enzyme recognizes only a single nucleotide sequence and once it finds this sequence in a strand of DNA, it splits the base pairs apart. This leaves single helix strands at the end of two double helixes, into which any genetic sequences may be added. The chain is then repaired as a longer chain that includes the added DNA with another enzyme, ligase.
Gene splicing will be applied to the most adaptable species of grass to be used for
phytoextraction, the most compatible remediation process. Grass is not currently a
hyperaccumulator, so the first gene to be modified will be the Metal Tolerance Protein 1, added to the DNA sequence of the species. Once a hyperaccumulator, the rate of growth must be augmented by inserting growth hormones and a gene that speeds the growth process. Although grass is a large plant covering an expansive surface area, the root system will be extended to maximize toxic uptake. A gene that does this will be transposed onto the genetic structure of the plant. It has been found that the trait attributed to hyeraccumulation is under monogenic control (the tolerance of each particular metal is controlled by a single gene). After absorbing the metal contaminants, the grass will simply be mowed and composted in order to collect the metals, while the grass regenerates itself. After five to ten years of crop rotation in this manner with the now ideal hyperaccumulator, all metal will be removed from the brownfield site. |
Though extensive research has been done on the study of phytoremediation,
scientists have yet to develop an ideal remediator. However, characteristics of such a
plant have been identified. An ideal plant would be a hyperaccumulator that can survive in contaminated soils while stimulating microbial growth. This is essential because the microbes actually break down the pollutants while the plants accelerate the degradation by supplying oxygen and nutrients through their root systems. They are then able to absorb the degraded contaminants. |
The ideal plant for this process is a hyperaccumulator. To effectively accumulate a
metal, a plant must be able to efficiently absorb it, translocate it through the xylem,
unload it into the shoot tissues, and finally, sequester it into vacuoles, which, much like the human liver, protect the plant from the metals' toxicity with a membrane-lined structure. It is believed that hyperaccumulation is the result of the enhanced or ectopic expression of a single component in one of these steps. Recently, however, scientists at Purdue University may have located the gene accredited to causing the process. The gene named by Dr. David E. Salt and his colleagues, Metal Tolerance Protein 1, was first identified in the Thlaspi goesingense plant and has been located in 350 known hyperaccumulators. However, the problem remains that these plants are small in scale and, therefore, inefficient and undesirable in widespread use as phytoremediators. |
The solution is to genetically modify larger plants otherwise containing desirable
characteristics to be hyperaccumulators. The best candidate for this is grass because of its
expansive surface area, adaptability to various climates, fast growth rate, regenerative abilities, and the ease with which it is harvested. The most effective gene transfer technique is genetic splicing because it is fast, precise and predictable, as opposed to other methods, such as hybridization and induced mutation. |
Before and After: One planting with tall fescue grass (right) was all it took
to clean the petroleum by-products out of a brownfield in Astoria, OR. (left)
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Therefore, it is also beneficial to have an
extensive root system in order to increase
surface contact with the soil. One of the major complaints of phytoremediation is its low efficiency due to the slow growth rate of the plants because it is necessary that they reach maturity and are fully functioning. Furthermore, most hyperaccumulators are too small to cause a significant effect. It is also necessary that the plant grows high off the ground for ease of harvesting and that it is adaptable to various climates. An additional problem is the potential volatilization of the pollutants after they have been absorbed by the plants. In the future, through improved knowledge of the genome of all possible phytoremediators, it will be possible to genetically enhance and combine the favorable characteristics of certain plants while altering or removing their negative and harmful tendencies. For example, a plant of the Brassicacea family, an extremely effective hyperaccumulator, is not ideal because of its slow growth rate and low-to-the-ground rosette architecture, which makes harvesting difficult. When the mechanics and specific gene structure of the plant's abilities are identified, they may be isolated and combined with a plant such as a poplar sapling, which is both high to the ground and able to mineralize the metallic compounds in soil. This process will produce an ideal remediator that is effective, efficient and safe. |
FUTURE
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Future Uses
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the extraction of gold, silver or other valuable metals that go undiscovered in the soil or exist only as trace
elements
To rejuvenate soil made infertile from overuse (improving food quality and productivity- an inexpensive
alternative for third world countries
benefits to the United States economy (increased reliance on domestic markets, significantly less
funding necessary for environmental remediation
aesthetically pleasing alternative to current remediation techniques- increase of property value and
stimulation of tourism industry
the extraction of otherwise unobtainable fossil fuels from soil, assisting energy deficiency predicament
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Transgenic Phytorejeuvenator Prototype
(before/after): This grass will be of the species
Sorghum vulgare sudanense (Sudan grass) because of it's fast rate of growth, adaptability to various climates, considerable height (this is essential because root length is directly proportional to the height of the grass, and for harvesting purposes). After genetic enhancement of the rejuvenator, previously inaccessible metal contaminants will be translocated and stimulated microbial growth will accelerate the degradation process. |