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Genetically Modified (GM) Crops: Debate of Pros and Cons

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Published: Wed, 16 May 2018

  • PHAM Thuy Linh

GM crops: Natural or unnatural?

For many of us, all we know about the food and vegetables that we consume daily are their shapes, their colours, their freshness, and how much they cost. Little do we know about the whole process behind the pack of banana or tomatoes in our bag: how were they cultivated? What pesticides were used on them? Or how were they harvested and stored?

Likewise, we may not know the long history in agricultural developments that enable large-scale food production at extremely low prices. 10000 years BC, people harvested their food from the natural biodiversity surrounding them and selected better plants for domestication. Over the years, farmers selected crops with better traits such as shorter growing seasons, stronger resistance to pests and diseases, larger seeds and fruits, nutrition content, and shelf life (Wieczorek, A. M. & Wright, M. G., 2012).

Agriculture has undergone major transformation. In particular, agricultural technology has made farming safer and more efficient. In particular, in agricultural biotechnology, a gene identified as having desirable traits will be selected, extracted, and transferred directly into another plant’s genome. Plant that has genes from others is called transgenic.

Comparison between Traditional Breeding and Genetically Engineered Crops

Crops produced through genetic engineering are referred to as genetically modified plants. All types of agriculture modify the genes of the plants so that they possess desirable traits. The difference is that traditional breeding changes the plant’s genetic indirectly by selecting plants with desirable traits while genetic engineering will make the changes directly to the plants’ DNA. In traditional breeding, crosses are made in uncontrolled manners and results are unpredictable as DNA from parents combine randomly. In contrast, genetic engineering permits highly targeted transfer of genes, quick and efficient tracking of genes in new varieties, and ultimately increased efficiency in developing new crop varieties with new and desirable traits (Wieczorek, A. M. & Wright, M. G., 2012).

Methods used in plant transgenesis

The method of genetic manipulation has been practiced for thousands of years by farmers who picked plants with desirable traits and cross-bred between two lines and repeated backcrossing between the hybrid offspring and one of the parents. However, crossing plants has many limitations. First of all, conventional breeding methods can only be carried out on sexually compatible plants and this limit the traits to those already existing in the plant strain. Secondly, the acquired desirable traits may come along with various undesirable traits as the parents’ DNA combine randomly. For example, a pest-resistant hybrid offspring may have undesirable traits such as low-yield or low-quality (Wieczorek, A. M. & Wright, M. G., 2012). Thirdly, unpredictable results and the possibility of undesirable traits make conventional breeding a time-consuming process as a lot of efforts are spent on repeated crossing until a new viable crop variety is attained. For example, Luther Burbank made 65000 crosses to achieve the white blackberry. Another method is using polyploidy plants to increase the desirable traits of the crops, especially size. This process allows the transfer of whole chromosome sets to the hybrid plants rather single genes and the additional chromosomes increased the size of the fruits and vegetables, which is commercially beneficial.

Plant transgenesis methods, on the hand, can overcome limits faced by traditional selective breeding methods such as species boundaries and sexual compatibility and provide significant benefits such as shorter time and certainty as well as the wealth of new strains and possibility of rare mutations and recombination. Compared to animal cells, plant cells possess one characteristic especially important in biotechnology: many plants can regenerate from a single cell-cloning-much easier than animals.

Methods

Procedures

Protoplast fusion

  • Plant cells’ wall is dissolved with enzyme cellulose leaving a denuded cell called protoplast
  • The protoplast is fused with another protoplast from another species to create a hybrid plant.

Leaf Fragment Technique

  • Small discs are cut from leaf
  • After the fragments begin to regenerate, they are cultured in a medium containing genetically modified Agrobacter (Agrobacterium tumefaciens), A soil bacterium that infects and triggers uncontrolled growth of cells
  • Leaf discs are treated with plant hormones to stimulate shoot and root development
  • A major limitation is that Agrobacter cannot infect plants that from a single seed embryo or monocotyledonous plants such as corn and wheat.

Gene Guns

  • This technique is useful for Agrobacter-resistant plants
  • A gene gun is used to blast tiny metal beads coated with DNA into an embryonic plant cell
  • DNA is often shot to the nucleus or the chloroplast
  • Researchers use marker genes to distinguish genetically transformed cells
  • A ‘hit and miss’ process

Chloroplast engineering

  • Chloroplast is the green plastid in land plants, algae and some protists
  • Unlike DNA in a cell’s nucleus, DNA in chloroplast can accept several new genes at once
  • High percentage of genes will remain active when the plant matures
  • DNA in chloroplast is completely separate from DNA released in pollen – no chance that transformed genes will be carried on wind to distant crops

Antisense technology

  • It is a process of inserting a complementary copy of the gene into a cell
  • Gene encoded an mRNA molecule is called an antisense molecule
  • Antisense molecule binds to normal mRNA (sense molecule) and inactivates it

Source: Thieman, P “Introduction to Biotechnology”

GM crops: Commercial successes and failures

Various studies have shown that demand uncertainty, market access, or market price can have a significant impact on GM corn adoption and diffusion (Alexander, Fernandez-Cornejo, & Goodhue, 2003; Fernandez-Cornejo, Alexander, & Goodhue, 2002). For example, GM crops offer producers a substitute for current pest control technology. The efficacy and cost of the current technology and the severity of the pest have a significant influence on adoption. For example Qaim and de Janvry (2003) found that Bt cotton adoption is positively related to the price of the chemical insecticides.

  • Flavr Savr Tomato

Flavr Savr Tomato was one of the first transgenic products commercialized. Compared to normal tomato that slowly rots due to the accumulation of PG, Flavr Savr tomato can last much longer due to the suppression of PG accumulation using Antisense technology. In particular, researchers at Calgene, now under Monsanto, first isolated the gene that encodes polygalacturonase, which encodes normal (sense) mRNA to be translated into PG. They then induced it to produce a CDNA counterpart and inserted the PG into a vector for transfer to tomatoes. The transgenic plants with the new insert will produce PG mRNA and antisense mRNA, cancelling the production of PG. They successfully created a tomato variety that can last about 3 weeks before ripening. However, the introduction of Flavr Savr tomato was controversial. Even though documents submitted by Calgene showed that PG-antisense tomatoes to be almost identical to traditional tomatoes besides its desirable trait, any products using the Flavr Savr tomato were soon boycotted due to public concerns. The Flavr Savr story reveals how difficult it can be to bring genetically engineered products to market, how objections with little or no scientific merit can influence the outcome, and how important public opinion is in determining commercial success (Bruening, G & Lyons J M, 2000).

  • Bt crops

Bacillus thuringiensis crops or Bt crops are insect-resistant as they are able to produce a toxin that kills insects and their larvae. For example, corn rootworm, often called the “billion-dollar bug’ for eating away billions of dollars of US farm profit through yield loss or control costs (Burchett, 2001). In 2003, Monsanto introduced a GM corn that is resistant to CRW (CRW corn); it produces the Bt toxin—which kills the CRW larvae—in the corn roots. Unlike the Flavr Savr tomato, the adoption of Bt corn is massive and has reached 26% of planted corn acreage in the United States in 2005, with another 9% of planted corn acreage in stacked gene hybrids that include the Bt gene (United States Department of Agriculture National Agricultural Statistics Service [USDA NASS], 2005).

  • Golden Rice

Golden Rice is rice that has been genetically modified to produce a large amount of beta carotene, which the body can convert to vitamin A. The Golden Rice, if adopted, will be able to save the lives of millions of children who die from blindness as a result if vitamin A deficiency especially in developing countries where rice is a food staple such as South and South East Asia (Easton, Nina, 2013). However, the Golden Rice has not been eagerly adopted by the target countries. For example, the China and Philippines continues to delay the introduction of Golden Rice for fear of public oppositions. In addition, the Golden Rice project’s effectiveness is actually limited by the fact that the pro-vitamin must be dissolved in fat before it can be used by the body so the poor who do not get enough fat in their diet may not be able to reap the full benefits.

Are we treating GM products fairly?

After learning about Plant Biotechnology and some of the achievements in terms of new crop varieties that help farmers and human kind to overcome natural limitations. I was surprised to read that GM crops are still widely and vehemently decried given the fact that we have already altered plants’ genomes through conventional selective breeding and hybridization. For example, March-on-Monsanto, held in May, is a movement against Monsanto, the corporation behind the food technology such as Flavr Savr Tomato and Bt crops. Globally, about 10 per cent of world’s agricultural land includes GM plants and 90 percent of the world’s GM crops are grown in the US, Canada, Brazil, and Argentina. The rest of Latin American countries choose to shun this technology. And even in the US, at least 20 states are considering GM-labelling bills in 2013. According to Goldberg, public fears are exaggerated and ill-founded and the debate about GM food should have ended years ago rather than going on and on for almost 40 years (Freedman, H 2013). Aimed with the foundation knowledge on genetics and plant biotechnology, I want to understand deeper the potential effects of GM crops: both beneficial and harmful from rigorous scientific findings and studies.

So is GM food evil?

GM crops have been argued to be a cause of genetic pollution in surrounding areas. Genetic pollution refers to the incident of uncontrolled and undesired gene flow into the wild populations. For example, the Bt corn produces wind borne pollen (able to spread 1km) that kills the caterpillar of the Monarch butterfly or the weeds that acquire the escaped genes became super competitive and can aggressively spread and kill other life forms in progress. According to Godheja (2013), if GM crops are bred with non-GM crops, there are a few possibilities:

  1. GM crops may lead non-GM crops to extinction
  2. Their genetics may change and they may not show their characteristics
  3. They may become resistant to herbicide and pesticide and become a challenge to farmers to control

Arguably, the uncontrolled spread of these genes may affect the consumers’ choice as they are no longer able to choose whether they want ‘organic’ or ‘GM’. For example, organic farmers in the US have found traces of genetically engineered DNA in their corn crops. It is hard for the organic farmers to point the fingers at the right culprit as the genetic pollution might be caused by pollen drift from GM fields from surrounding areas or even contaminated seeds.

Concerns about human health risk is also a major obstacle to adaptation of GM crops. For example, the potential of GM crops to be allergenic is one of the main suspected adverse health effects, due in part to research by Hi-Bred in the mid-1990s. They discovered that soy bean plants engineered with a gene from Brazil nuts produced beans that caused an allergic reaction in some people (Godheja, 2013). In addition, some of the current GM foods contain antibiotic resistance genes, which could contribute to the spread of pathogenic microorganisms that are immune to the antimicrobial agents currently available (FSA report, 2002). In addition, there is a general concern that the transfer of plant-derived transgenes to the resident gut microflora could have safety implications. Despite previous assumption that plant-derived transgenes will not transfer to the intestinal microflora because the nucleic acid will be rapidly and completely degraded by the digestive enzymes, studies by Schubbert, R et al (1994) and (1997) showed that bacteriophage M13 DNA, fed to mice, was detected in the faeces, indicating that a proportion of the DNA survives in the GI tract. In addition, this group detected the phage DNA in the liver demonstrating that the nucleic acid was able to pass through the intestinal epithelium into the systemic circulation (FSA report 2002).

In addition to the transfer of antibiotic resistance another mechanism of gene transfer which can adversely affect human health is from microorganisms to intestinal epithelial cells (FSA report 2002). It is known that prokaryotes can adhere to the gastrointestinal epithelia, which some bacteria can invade intestinal enterocytes, and these interactions could result in gene transfer from the microorganisms into the mammalian cells (FSA report 2002). This view is supported by data demonstrating that bacteria can be used in gene therapy strategies designed to deliver DNA into mammalian cells.

However, significant risk that genetically modified plants and bacteria can transfer their transgenes to other organisms in the intestinal tract of humans: a significant proportion of the transgenes in GMPs does survive in vitro simulations of the small bowel (Martin-Orue, S et al 2002) and bacteriophage M13 DNA gavaged into the mouse intestines is detected in the faeces, blood and liver (Schubbert, R et a 1994, 1997, 1998). Netherwood found that transgenes in genetically modified Soya survive passage through the human small bowel but are completely degraded in the colon.

Public debate

While anti-GM groups often disparage U.S. research on the safety of GM foods, which is often funded or even conducted by GM companies, such as Monsanto, much research on the subject actually comes from the European Commission, the administrative body of the E.U., which cannot be so easily dismissed as an industry tool (Freedman H 2013). In particular, there are 130 funded research projects by European Commission, 500 independent teams, on the safety of GM crops, none of which concluded on any special or significant risks from GM crops. On the contrary, the use of genetic engineering has lowered food price and made it safer due to smaller usage of pesticides and herbicides. David Zilberman, a U.C. Berkeley agricultural and environmental economist, argued that benefits of GM crops outweigh the health risks, which so far has remained theoretical. Opponents also cited various studies indicating possible safety problems. However, almost all of those reports have been refuted. For example, a 1998 study by plant biochemist Árpád Pusztai, then at the Rowett Institute in Scotland, found that rats fed a GM potato suffered from stunted growth and immune system-related changes. But the potato was not intended for human consumption — it was, in fact, designed to be toxic for research purposes (Freedman ,2013). The scientist was later charged with misconduct.

Conclusion

While I believe the debate on the safety of GM foods will continue with no definite conclusion in the near future, I believe that there is much more benefit to this technology than depicted by the mass. Thanks to my knowledge of Biotechnology, I am able to develop my own stand on this topic rather than relying what the mass opinions. In my opinion, there are definitely GM plants that should be adopted immediately such as Golden Rice. Other crops may require further testing before being deemed completely safe for human and the surrounding ecological systems.

References

Wieczorek, A. M. & Wright, M. G. (2012) History of Agricultural Biotechnology: How Crop Development has Evolved. Nature Education Knowledge 3(10):9

Verma http://www.aidic.it/IBIC2008/webpapers/96Verma.pdf

Peterson, G., S. Cunningham, L. Deutsch, J. Erickson, A. Quinlan, E. Raez-Luna, R. Tinch, M. Troell, P. Woodbury, and S. Zens. 2000. The risks and benefits of genetically modified crops: a multidisciplinary perspective. Conservation Ecology4(1): 13. [online] URL: http://www.consecol.org/vol4/iss1/art13/

Bruening, G & Lyons J M, 2000, The case of the FLAVR SAVR tomato, California Agriculture 54(4):6-7 Available at http://ucanr.org/repository/cao/landingpage.cfm?article=ca.v054n04p6&fulltext=yes

WHY THE MARCH ON GENETICALLY MODIFIED FOOD HURTS THE HUNGRY. By: Easton, Nina, Fortune, 00158259, 6/10/2013, Vol. 167, Issue 8

Are engineered foods evil? By: Freedman, David H., Scientific American, 00368733, Sep2013, Vol. 309, Issue 3

Schubbert, R., Lettmann, C. and Doerfler, W. (1994) Molecular and General Genetics 242, 495-504

4 Schubbert, R., Renz, D., Schmitz, B. and Doerfler, W. (1997) Proceedings of the National Academy of Sciences U.S.A 94, 961-6


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