Genes that changes the oxidation state of heavy metals [Case Study]

It has been known that no plants even to this date; have been found with natural ability to accumulate or degrade mercury.

Through the use of transgenic plants, phytovolatilization have been developed to remove mercury. Some bacteria in mercury contaminated site are discovered to be able to convert organic mercury to elemental mercury that is less toxic. The elemental mercury move out of the bacteria and is volatilized to be release into the atmosphere. Organomercurial lyase (Mer B) and mercuric reductase (Mer A) are enzymes responsible for this process.

Mer B converts organic mercury (CH3Hg) to ionic mercury Hg (II), which is then reduced to the volatile elemental mercury Hg (0) by Mer A. The two genes that produce Mer A and Mer B enzymes were introduced in Arabidopsis thaliana plant. Result shows that the transgenic plant were able to grow in concentration of organic mercury fifty times greater than control plants. Furthermore, results have shown that the transfer of Mer A to yellow poplar plant enhances its ability to volatilize ten times more mercury than control plants.
Eastern cottonwood, Populus deltoids, another candidate plant used for phytoremediation, was modified with Mer A gene. The transgenic shoots grew normally on a medium with 25 μM ionic mercury Hg (II), a concentration which killed wild-type shoots. In addition, the transgenic plant generated up to four times more elemental mercury Hg (0) than wild-type plants. This evidently shows that the plants are capable of transforming mercury to its less toxic form more efficiently.

An experiment is carried out in polluted soil with mercuric ion at a toxic concentration of 400 ppm Hg (II). By two weeks, all the non-transgenic plant had died while the transgenic cottonwoods were still alive.

Genetically modified food, a solution to rising concerns of air pollution

In order to help with the reduction of CO₂ emission in the world, genetically modified (GM) crops have an immense capability of protecting the environment, or so says an agricultural economist.

According to studies conducted by Graham Brookes of PG Economics from United Kingdom, the use of GM crops has reduced carbon dioxide (CO2) emissions by an estimated 14.76 billion kilos in 2006. From 1996 to 2006, the growth of GM food has caused a reduction in the use of pesticides by 15.47%.

An example of such usage is the GM insect-resistance cotton, which has reduced 5.6 million kilos of insecticide since spraying has ceased. By doing so, less fuel is used, reducing CO₂ emission by 5.8 billion kilos, which are about 2.6 million cars off the road.

Biotechnology crops is also said to promote low or no till farming, a system which cancels release of 13.5 billion kilos of CO₂ into the atmosphere. Further till farming can reduce another 63.9 billion kilos of CO₂.

Another advantage is the financial side of it. Production of GM crops can generate an accumulated income of $33.8 billion, which can also lower food prices, especially in developing countries.

 

How genetic modified food came about

A sense of genetic engineering is simply, conventional plant breeding. It can manipulate the genetic makeup of plants toward a desired combination of traits. In order to get this particular gene through conventional plant breeding, the two lines are sexually crossed to give first generation hybrids a genetic pattern deprived from the parent gene. These hybrids are grown repeatedly and back-crossed with one of the parent gene until a desired genetic makeup emerges. This plant will have most of the genes from one of the plant, yet it will contain characteristics from the other parent as well. This process is known as introgression.

Because of its conventional way, such processes are usually slow and take several years, although there are techniques to accelerate it. In addition, transfer of genes from one plant to another cannot be controlled, and some favourable genes may be coupled with other undesirable genes. Furthermore, breeding of such plants are only restricted to sexually compatible species, and thus impose a limitation on the species in the gene exchange.

However, there are a lot of plants with unusual genes that exist outside their own natural species barrier. Some examples include the cactus, which can tolerate long period in dry soil conditions and tropical plants that are resistant to pathogens and insects. Because of the existence of such genes, instead of worrying about the natural species barrier, the aim is to introduce single gene with their defined functions into useful plants. To do this, two things need to be done. One is obtaining such genes in pure form, and next, finding a way to get these genes into plant chromosomes.

The process in which genetically modified food is created

After genes of interest (they may be from plants, bacteria, fungi, viruses, or animals) are characterized for their functions, they are then hooked up with a promoter, a regulatory segment of DNA that activates genes.  This promoter-gene combination will be inserted into a vector (small loops of DNA) that will be ready for plant transformation.  The vector carrying the promoter-gene segment is called a Construct. There are two major transformation technologies for inserting genetic materials into plants, Agrobacterium-mediated transformation – a natural delivery system and biolistic gun-mediated transformation – a physical delivery system (gene gun).

Agrobacterium tumefaciens is a common soil bacterium that scientists have known since the mid-70s. The genetic segment of the bacteria is to be inserted into the plant genome, and the plant would express the foreign genes in the form of protein. In this method, the Agrobacterium strain will carry the Construct and incubate with plant tissue, transferring the gene into the plant cells.

The gene gun was invented in 1984 to introduce DNA into cells by physical means in order to curb the biological limitations set by the Agrobacterium, since not all plant tissues “infected” by the bacteria is able to grow into a plant after the infection.

In this biolistic (biologic ballistic) process, construct DNA is coated on the surface of gold particles (0.6 – 1 mm in size).  The DNA-coated gold particles (microprojectiles) are accelerated by helium gas to speeds sufficient for the penetration of plant cell walls and membranes.

After delivering genes into plant cells, the challenge is to effectively identify the few transformed cells among millions of untransformed cells.  One device used for selection is that the vector carrying the gene of interest (GOI) also carries a selectable marker gene such as an antibiotic resistant gene or herbicide resistant gene. Cells like this that transforms from the GOI usually carry such selectable markers so that when the cells are grown in mediums with antibiotics and herbicides, only the transformed cells will survive, while the non-transformed cells will die.

Enzymes that detoxify active ingredients of herbicides are also inserted into crops. They are usually isolated from bacteria, fungi or virus and some plant species, and are in limited numbers of commercial transgenic crops with enhanced output traits.

 

Benefits of genetically modified food

Holds great potential for reducing global hunger and malnutrition through increased yields and improved quality.

Future GMO products are projected to include crops with pharmaceutical benefits, vitamin-enhanced grains, and those with amino acids and other nutritional features that are better suited to human needs than current varieties.  Crops with increase drought and extreme-temperature tolerance, and resistance to a variety of pests and diseases also are envisioned to be developed.

An example is corn. As of now, the current GMO technology includes “Bt” corn, corn plants that have DNA from Bacillus thuringiensis (Bt), a bacterium producing a protein (Bt-toxin) which is designed to resist corn borers, an insect which attacks and weaken plants. They damage the stalks and reducing yield potential, increasing the risk of corn plants falling over before they are harvested. The crops are made more vulnerable to damage by wind, dropping of ears as that a part of the production cannot be harvested.

The infestation of this insect depends on the geographical location every year. Areas near the west of the Mississippi River, known as the Corn Belt tend to have greater problems.

So far, world grain production has outpaced the increase in the global population through the use of non-GMO technology.  However, the long term ability of global agriculture to supply enough food for an expanding population is uncertain.

Unabated population growth shows a continuing need for priority on agricultural research to increase yields, although the persistent supply increases of recent years have placed downward pressure on commodity prices.  There is no indication that supply increases will be less robust in the future than in past decades, even without transgenic crops.

Today, most GMO food are pretty good at reducing the number of herbicides that farmers used to control weeds, facilitating minimum tillage or no-tillage farming, reducing soil erosion and surface water contamination.  “Bt” corn also eliminates the need for use of insecticides that can cause various types of environmental contamination

Disadvantages of GM Food

A major disadvantage of GMO food is the environmental implication. For example, the U.S. agriculture has decided on the use of “integrated crop management”, which is the use of pest management selectively, especially in areas where corn borers infestation are highly and likely. However, the “Bt” corn, which is grown, is being used every year, and while it is resistant to corn borers attack now, there are concerns that a Bt-resistant borer may develop. Not surprisingly, “Bt” corn pollens have also been found to increase the mortality of Monarch butterfly larvae, a completely harmless insect, among some other butterfly species that may be similarly affected.

Apart from implications on the insects, there have been concerns expressed that ‘super weeds’ might develop a resistant against herbicides. On the other hand, GMO crops may also cross breed with some other closely related species, developing herbicide resistant wild varieties of crops. Similarly, there might be also a ‘terminator’ gene that crosses the native varieties of crops, causing both environmental problems and loss of genetic resources. These kind of accidental cross breeding is feared to reduce the genetic base that is needed for future research. And as Mr Andrew Pollack, wrote on “We Can Engineer Nature. But Should We?” in the New York Times, February 6, 2000 edition, and I quote, “What is particularly worrisome is that because biological systems reproduce, such genetic pollution cannot be cleaned up like a chemical spill or recalled like a defective automobile. Once the gene is out of the bottle, so to speak, it cannot be put back in”.

Case Study – GM Food in America

Natural selection has resilient biological systems which ensure the development of an organism contains the properties it needs to adapt to vary environmental conditions and to ensure the continuation of such species. However, conventional plant breeding, a subset to genetically modified organisms, breaks down these systems, creating their own gene combination that would rarely survive in nature.

Impacts from these conventional plant breed species can be deadly to both the environment and the farmers, should they not be bred well. While most of the food that are being bred around the world are not native to their major production zone, through the times of migration and trade, these plants are grown all round the world, and they do not create any serious problems as of yet. An example is maize from Mexico. Hybrids genes from both conventional bred and wild species have been said to flow within the plants, but it is still not considered a problem.

The real problem is, however, transgenic food. This occurs when a particular plant species is being contaminated by genetically modified organisms. A contamination on pollen from GM corn that was blown over from another farm and whose patented gene was the same one picked up in the test.
This will result in what environmentalists call, “transgenic” pollution.

Organic crops pollinated with biotech genes can lose their organic status if they have been cross polluted. Growing like these takes three years to accomplish, and when if such a situation would to occur, the farmer would be the one to suffer financially.

The National Farmers Union in Canada, for example, has made biotech films to be liable for any “genetic pollution” that occurs, while in the United States, farmers had made sure that should anything happen to their crops, they know who exactly are the people to find.

While GM food has shown to make sure the use of pesticides and herbicides decrease, it has also taken a toll on the economy on countries that rely highly on agriculture.

America, which have genetically modified crops that covers over 90 million acres, which is about a quarter of the country’s entire cropland, is one example. Being on the large scale GM food growing countries, all the farmers may be feeling the pinch when countries like Brazil, Japan and Australia have pledged to restrict GM food. This have resulted in a loss of almost $1 billion in US agriculture, a fairly large amount.

Most of the GM seeds on the market have been engineered to make crops more tolerant of pesticides or to carry their own pesticide.

Bt spray that are being frequently used by organic farmers degrades easily in the soil, but those in Bt corn, the pesticide is in the food and doesn’t wash off, being at its full potency at all times. No one knows what the health effects of consuming those are, and at what doses does it adversely affect our health.
Another issue raised by organic farmers are that Bt crops could create a class of insects resistant to it, rendering their spray, which is the most effective weapon and last line of defence now totally useless.
While some international seed companies are still maintaining their alteration of crops to contain the Bt to decrease the need of chemical pesticides to benefit the environment, the Biotechnology Industry Organization reported that the introduction of Bt corn has only reduced the use of pesticides by 2.5%. However, the use of insecticide remains the same for both corn breeds, showing no difference.

Charles Benbrook, a biotechnology consultant for Consumers Union and former head of the National Research Council’s board on agriculture, argues that “while Bt corn might work for a few years, those gains would be offset by big problems long term.

“The real problem,” he believes, “is that saturating the soil with these novel organisms will shift the competitive balance in the soil and stimulate other pests moving in. And by taking away farmers’ use of Bt as a spray, genetic engineers are robbing them of a most valuable tool.”

According to the United States Department of Agriculture (USDA), there are about 40 plant varieties that have met all federal requirements and could be used in trade. Some of these plants include tomatoes that have been able to ripe faster, soybeans that are resistant to herbicides and corns that are resistant to insects. These products may not be available for sale yet, but most of the food found in grocery shops in U.S. is said to contain genetically modified food, in one form or another.

As of 2000, there have been thirteen countries which are known to grow genetically modified crops. 68% of such crops come from the U.S., while the remaining 32% came from countries like Canada and China.
Soybeans and corn are the top two most widely grown crops (82% of all GM crops harvested in 2000), 74% of these GM crops were modified for herbicide tolerance, 19% were modified for insect pest resistance, and 7% were modified for both herbicide tolerance and pest tolerance. Globally, acreage of GM crops has increased 25-fold in just 5 years, from approximately 4.3 million acres in 1996 to 109 million acres in 2000

In the U.S., the two main food products have made the most impact in the genetically modified crops industry. Approximately 54% of all soybeans cultivated in 2000 were genetically-modified, up from 42% in 1998 and only 7% in 1996. GM corn and also experienced a similar but less dramatic increase. Corn production increased to 25% of all corn grown in 2000, about the same as 1998 (26%), but up from 1.5% in 1996. Pesticide and herbicide use on these GM varieties was slashed, resulting in increase of yields.

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