Question

Glyphosate (Roundup) is a very effective herbicide that is toxic to almost all types of plants. a. Why is glyphosate considered an animal-safe herbicide? b. Why does it take up to 7 days before there is any noticeable herbicidal effect of glyphosate? c. Why don't Roundup Ready soybean plants die when they are sprayed with glyphosate?

Short answer

Answer: Roundup Ready soybean plants are genetically engineered to be resistant to glyphosate. They contain a modified version of the EPSPS enzyme, which is not affected by glyphosate, allowing the production of aromatic amino acids and enabling the plant to continue growing and surviving even when sprayed with the herbicide.

Step-by-step solution

a. Animal-safe herbicide

Glyphosate is considered an animal-safe herbicide because it targets a specific enzyme found in plants, called 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). This enzyme is involved in the production of aromatic amino acids, which are essential for plant growth. Animals, including humans, do not have this enzyme in their metabolic pathways. It does not target any specific enzymes or metabolic pathways in animals, making it safe for them.

b. Herbicidal effect taking time

Glyphosate takes up to 7 days to show noticeable herbicidal effects because it acts on plants by inhibiting the EPSPS enzyme, which in turn disrupts the production of essential amino acids. This disruption leads to a slow death of the plant as it is unable to synthesize the necessary proteins for growth and survival. The process is not immediate and requires time for the plant to exhaust its reserves of proteins and amino acids, eventually leading to its death.

c. Roundup Ready soybean plants

Roundup Ready soybean plants are genetically engineered plants that have been modified to be resistant to glyphosate. These plants contain a special version of the EPSPS enzyme, which is not affected by glyphosate. This modified enzyme still allows the production of aromatic amino acids, thus the Roundup Ready soybean plants can continue to grow and survive even when sprayed with glyphosate. Consequently, the herbicide can kill the surrounding weeds without harming the soybean plants themselves.

Key concepts

EPSPS Enzyme

One of the crucial elements in understanding the efficacy of glyphosate herbicides, such as Roundup, is the EPSPS enzyme. Standing for 5-enolpyruvylshikimate-3-phosphate synthase, this enzyme is a key component in the shikimic acid pathway, which is an essential biochemical process in plants, fungi, and bacteria. The shikimic acid pathway is responsible for the biosynthesis of aromatic amino acids like tyrosine, tryptophan, and phenylalanine. These amino acids are not just building blocks of proteins; they also play a pivotal role in the synthesis of other important compounds that are involved in the plant's structural integrity and defense mechanisms.

Glyphosate's effectiveness as a herbicide comes from its ability to inhibit EPSPS. Without a functional EPSPS enzyme, plants cannot produce these vital aromatic amino acids, eventually leading to plant death. The specificity of glyphosate toward EPSPS makes it safe for animals, which do not utilize the shikimic acid pathway and, therefore, lack this enzyme. This targeted mechanism of action is why glyphosate takes a while to exhibit its herbicidal effects; plants gradually deplete their existing amino acid reserves before the inhibition leads to noticeable damage.

Roundup Ready Soybeans

Roundup Ready soybeans represent a significant advancement in agricultural science, embodying the successful integration of genetic modification to solve practical farming issues. The term 'Roundup Ready' refers to soybean plants that have been genetically altered to withstand the herbicidal effects of glyphosate. This genetic modification involves the introduction of a gene encoding a version of the EPSPS enzyme that is not affected by glyphosate.

This innovative approach means that farmers can spray Roundup across their fields to control weeds without worrying about harming their crop. As a result, soybean plants continue to produce essential aromatic amino acids and grow healthily, giving these crops a strong advantage over weeds. The modification has led to more efficient farming practices, as it simplifies weed management and reduces the need for tilling, which can be harmful to soil quality and sustainability.

Aromatic Amino Acids Synthesis

The process of aromatic amino acids synthesis is vital for plant life. These amino acids - tyrosine, tryptophan, and phenylalanine - are not only components of proteins but are also precursors for numerous plant secondary metabolites. These metabolites include flavonoids, which are important for UV protection, pigmentation, and defense against pathogens. The synthesis occurs through the shikimic acid pathway, making this process a target for herbicide action, as seen with glyphosate.

Herbicides that target this biochemical pathway are highly effective because they disrupt a fundamental process of plant metabolism, leading to the gradual cessation of growth and eventually, plant death. However, it's also the reason why the effect isn't immediate. A plant has stores of aromatic amino acids and associated secondary metabolites that need to be depleted before the plant's growth is visibly affected.

Genetic Modification of Plants

Genetic modification of plants is a process by which plant genomes are altered to achieve certain traits, such as resistance to pests, diseases, or herbicides, improved nutritional content, or better yield. The technology involves inserting genes from other organisms, which can confer these desirable traits. In the case of Roundup Ready soybeans, geneticists have introduced a gene that gives the plant a glyphosate-resistant version of the EPSPS enzyme.

This alteration allows farmers to use glyphosate as an effective weed control without damaging their crops. It's a breakthrough that has reshaped soybean farming and has implications for food security and agricultural sustainability. Nevertheless, the use of genetically modified organisms (GMOs) is subject to ongoing debates concerning biosafety, environmental impact, and ethical considerations. Therefore, while genetic modification offers incredible benefits, it also demands careful regulation and continued scientific research to ensure its safe and beneficial integration into agriculture.