840.119:Herbicide Resistance

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840.119: Introduction to Biotechnology


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This website will be used to describe the process, purposes, and risks of developing glyphosate resistance in tobacco plants. The herbicide glyphosate has been around for over twenty years and since the technological advances in genetically modified organisms, the development of a resistance in crops has become a desired and beneficial product.

State of the Art

Tobacco plants that have been modified for glyphosate resistance are currently being used by farmers and the results of the resistance to the herbicide have been successful. Widespread use of glyphosate resistant crops such as soybeans, cotton, and tobacco have been used since the late eighties, early nineties. About eighty percent of the U.S. market in the farm crops is now in plants that tolerate glyphosate. Glyphosate is a safe and inexpensive herbicide, that is potent yet enviornmentally friendly so it has a great appeal, it has been trademarked as "Roundup". Because of the qualities that glyphosate possesses, resistance to the herbicide in crops is very important.

Monsanto, the company that invented the herbicide glyphosate has been very successful being that until recently it was the only company that commercially produce glyphosate-tolerant plants. Recently in 2000, the patent on the herbicide has expired, so other companies are now trying to have success in herbicide protected plants and break the monopoly that Monsanto's success has created.

Herbicide resistance is the most widely planted transgenic crop trait. About 75% of all genetically modified crops are engineered for herbicide resistance.


The main objective of this website is to discuss the impacts and risks associated with glyphosate resistance. We will also discuss a bit about how glyphosate works and the technology behind developing glyphosate resistance.

Scientific approach

Methods Used

Fig 6 10.jpg

"If the Agrobacter TDNA contains bacterial DNA encoding EPSPS (a photosynthesis enzyme), in a cholorplast targeting sequence, it can be transferred into a plant. When the promoter (CaMV) is activated, it allows the plant (tobacco shown) to produce the bacterial EPSPS enzyme and resist the high level of glyphosate that otherwise would inhibit the natural enzyme in the plant. In this way, both plants and weeds can be sprayed with glyphosate and only the nontransformed plants are affected." (Thieman, 144)

Alternative Methods, Why aren't they used?

Researchers have been looking for herbicides that will spare the crop, but kill the pest. Often crops and pests have similar biochemical properties, therefore finding an herbicide that won't affect both has been difficult. Today, with new advances in biotechnology, researchers have found it to be more beneficial to use genetic engineering to create a crop that is less susceptible to glyphosate-based herbicides.

(Potential) Impact

The development of herbicide resistant crops has helped spare the environment from harsh chemicals and reduce the cost to farmers on chemicals for pest control. Chemicals in herbicides designed to be used on herbicide tolerant crops tend to be much more environmentally friendly and much milder than those used on non-tolerant crops. Also, the price of these milder chemicals is much less than traditional herbicides.

Associated Risks

One of the potential risks that is associated with the development of herbicide resistance in tobacco plants is that with only one primary method of controlling weeds, some are worried that the weeds will become resistant themselves and this method will no longer be useful. With glyphosate as the primary herbicide there is potential for this. With such a high percentage of crop plants being herbicide resistanct it has cut down the use of other herbicides to virtually none. Some have suggested that with other herbicides on the market it is important to incorporate them all into use. It would make it necessary to produce crop plants resistant to the other herbicides, but it could also save the tool of herbicides, and herbicide resistance. If weed species are subject to only one form, and they do become resistant evetually, it could eliminate the entire tool and the time and money saved by the process of the herbicide and herbicide resistant crops.

Scientists are also concerned that since most crops are modified by inserting genes into the nucleus, the genes will be able to spread to other crops or wild relatives by pollen movement. However, Daniell et al has now found a way to engineer tolerance into the tobacco chloroplast genome. Cholorplasts are maternally inherited, so the risk of the modified genes escaping is cut off by this new method.

Ethical issues


Benbrook, Charles M. 1986. "Engineering Crops to Resist Herbicides." Technology Review 89:54-59.

Miller, Julie Ann. 1985. "Gene Splicing for Herbicide Resistance." Science News 127:140.

Stokstad, Eric. 2004. "A New Task on Herbicide Resistance." Science 304:574-1089.

Thieman, William J. and Michael A. Palladino. 2004. Introduction to Biotechnology. 136-149.

Ye, Guan-Ning and Peter T.J. Hajdukiewicz. 2001. "Plastid-expressed 5-enolypyruvylshikimate-3-phosphate synthase genes provide high level glyphosate tolerance in tobacco." The Plant Journal 25:261.