|Protester dressed as a superweed|
CC photo by Steve Rhodes on Flickr
Glyphosate interferes with a plant enzyme key to the production of, for example, auxin (a plant growth hormone, also important in reproduction), lignin (woody supportive material), and defensive compounds against pests and disease. All of these are vital and are part of tightly controlled processes in a healthy plant. When glyphosate wipes out that enzyme, the weed or non-GM plant dies.
The magic gene inserted into glyphosate-tolerant crops generates a novel version of the enzyme which isn't inactivated by the herbicide. However, the expression of an artificial gene, isn't controlled. GM glyphosate-tolerant plants will therefore generate an excess of the enzyme, and this suggests that their growth, reproduction, physical robustness, and susceptibility to disease will be altered.
Indeed, unexpected yield increase and lignin excess  in herbicide-tolerant GM plants have been observed. Two teams of scientists (one Chinese, one American) have extrapolated these side-effects to the question of what will happen when the artificial gene (along with the super-abundance of artificial enzyme it generates) ends up in weedy relatives of the GM crops?
It's always been assumed that, in the absence of spraying with glyphosate, weedy GM plants would have no particular advantage and wouldn't be a problem. However, science tells a different story.
It seems weedy glyphosate-tolerant plants may have a huge potential to become superweeds, or, to be precise SUPERWEEDS. These will not only withstand the herbicide most likely to be sprayed on them, but even in the absence of the herbicide, will grow bigger and produce up to 37% more seeds with enhanced germination under stress. This won't of course happen in every GM-weed hybrid, but the few plants it does happen in could quickly swamp the environment. The effect could make the GM weeds especially invasive under heat- or drought-stress at the same time as their competitors are succumbing.
Are we seeing an interesting phenomenon in which a GM plant primed by the stress of an artificial gene then reacts to further stress by increasing reproduction? This might not be limited to the glyphosate-tolerance gene.
It's also been pointed out that GM weeds which are initially disadvantaged by acquiring their novel gene may go on to evolve compensatory mechanisms and become superweeds over a few generations.
The big question here is why it's taken more than two decades to start researching a potentially devastating problem for future agriculture which could have been predicted.
The experiment used 'Arabidopsis', a common, fast-growing, well-characterised plant model, and might not translate into what will happen in the field. But then again, weeds are smart: the model might equally be under-stating the problem.
Before we are poisoned by escalating quantities and cocktails of herbicides applied to escalating SUPERWEEDS, let's get rid of the simplistic GM model of designer crops plants.
 ADVERSCIENCING - GMFS Archive, February 2009
- Zachery T. Beres, et al., 2018, Overexpression of a native encoding 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) may enhance fecundity in Arabidopsis thaliana in the absence of glyphosate, International Journal of Plant Science 179(5)
- Jia Fang, et al., 27 February 2018, Overexpressing Exogenous 5-Enolpyruvylshikimate-3-Phosphate Synthase (EPSPS) Genes Increases Fecundity and Auxin Content of Transgenic Arabidopsis Plants, Frontiers in Plant Science 9
- Glyphosate resistant plants show a surprisingly high potential for uncontrolled environmental spread, www.testbiotech.org, 6.04.18