What is Modified in a Genetically Modified Crop?

Genetically modified organisms are coming in for bad press, but some of the criticism is distorted.  The implication is that if we give this stuff up we will be fine; but we won’t necessarily. Let’s hold the polemic and explain what is afoot in the world of genetically modified organisms.  Many Universities with an agricultural faculty maintain websites on GMO crops, including Colorado State University and they are useful to consult.

One of the earliest GMO products was corn that carried a gene for a toxin called Bt, which comes from the spore forming bacterium Bacillus thuringiensis. The toxin is actually a crystalline protein that is activated in the intestine of some insects. The toxin made by the bacteria paralyses the gut of feeding insects and they die of starvation, before they consume the plant. The digestive tracts of insects are at relatively high pH, those of animals are acid, which kills the toxin. Bacillus thuringiensis can be found almost everywhere in nature, including most hardware stores or on the Internet.

Farmers are not gardeners; they work on a huge scale in a very risky venture. Their crops must survive drought, flooding, insects, fungi, and weeds if we want to eat.  To help with insect pests, the piece of DNA that provides the instructions for the Bt toxin was inserted into the DNA of corn, cotton, soybeans and other plants. This works.  The insect pests of corn, (or maize), are killed by the Bt toxin that is produced in the leaves.  Plant molecular techniques are now so developed that the toxin is not expressed in the flowers or pollen of the plants, but only in the leaves. When the Bt toxin gene is expressed in corn or cotton, the plant is not considered organic.

Top: Lesser cornstalk borer larvae extensively damaged the leaves of this unprotected peanut plant. (Wikepedia Commons, Image Number K8664-2)-Photo by Herb Pilcher). Bottom: After a few bites of peanut leaves of this genetically engineered plant the corn borer larvae are dead. 

Worm resistant corn, in this case a strain made by Syngenta. Resistant corn is on the left. 

The Bt toxin was one of many genetic modifications put into plants. Another inserts a gene that makes the plants resistant to glyphosate  (Roundup), also available at Home Depot.  Spraying Roundup on a field reduces weeds, without killing the genetically modified corn, soybeans or cotton. When the leaves absorb glyphosate, it inhibits the production of three amino acids, and the weed slowly dies for lack of component parts for its essential proteins. Roundup does not inhibit the enzyme that makes these amino acids in other organisms, so if that gene is put into crop plants, the weeds die and the crops don’t. In both cases the new protein made by the plant has a known function and the other 20,000 or more proteins that a plant requires for life are not affected.

Sometimes both systems are put into the same plant, such as sugarcane. In 2010, 70% of corn, 78% of cotton and 93% of soybeans grown in the United States were genetically modified to resist insects, weeds or both. Wheat is not modified, largely because it is a major export crop and some importing countries will not accept it.

This is not to say there are no problems, such as insect resistance. Anyone who has studied evolution knows that there will be.  There may be effects on beneficial insects. Or, to my mind the most important problem is that such a technology gives too much power to a few gigantic corporations. Their ability to dictate to farmers is a big worry.

But to return to safety issues. Recently, the controversy has coalesced around a disputed study by a group at the University of Caen in France. The group, led by Dr. Gilles-Eric Séralini, did a massive study, lasting two years, in which groups of rats were fed a diet of unmodified maize or one of three concentrations of genetically modified maize.  Some rats also got Roundup in their drinking water.  Enormous numbers of tests were done on the rats and the conclusion was that the genetically modified corn and Roundup caused cancer.

The paper was published in the journal Food and Chemical Technology, and was immediately attacked by critics. Some protests may have been agribusiness induced, some were not.  Opponents of GMO crops were outraged at the criticism of Dr. Séralini and his colleagues, especially when Food and Chemical Technology’s editor-in-chief retracted the paper.

This blog will try to explain the science behind such controversies, even if the passions around an issue have so polarized people that it is hard to explain where the evidence points. So I read the Séralini paper. My conclusions will appear in the next blog.

Demystifying Science

My blog tries to explain the basic mechanisms of science to non-scientists. Many of the blogs come from columns written for The Lakeville Journal in Lakeville CT. These columns have a number of themes, but among the most important is the value of basic science. It is curiosity driven, may have no immediate use and costs money, but it has given rise to everything that is useful in science and medicine. We also encourage skepticism.

We often write about vaccines to explain how they work and what progress science is making. The current blogs are focused on Genetically Modicifed Organisms and according to our theme, try to explain mechanism. Another focus if the value of vaccines.

Science has evolved methods that are the best way for us to understand the natural world, whether it concerns the death of chestnut trees or the death of neurons. Scientists search for theories to explain natural phenomena and these can be disruptive – as with evolution or cosmology or climate change. 

When writing for non-scientists it helps to have a non-scientist as a critic and for this we thank Mrs. Susan Maclin of Houston, Texas. If she doesn’t understand a column it gets rewritten.