The use of herbicides and their secondary effects on the synthesis of important amino acids

In agriculture, amino acids play an important role in the metabolic chain of plants and are directly linked to protein synthesis, root development, stress metabolism, hormonal precursors, increased photosynthesis, nutrient absorption, among other important characteristics essential to plants to achieve high production ceilings. Amino acids have common structural characteristics and are formed by a central carbon, almost always asymmetric, linked to a carboxyl group (OOH), an amino group (NH2) and a hydrogen atom (Castro 2008). A chain of amino acids forms a protein and depending on which amino acids come together and how they are organized, different proteins are formed (Taiz & Zeiger, 2004). More than 500 amino acids are known in nature, however, only 20 are considered essential, as well as tryptophan, glutamic acid, phenylalanine, tyrosine and proline, for example.

Herbicides are compounds that have important biological activity for food production (STEPHENSON et al., 2006). The chemical control of invasive plants is one of the extremely important aspects of achieving high productivity parameters in the production of grains, fibers and cereals, as they compete directly for water, light and nutrients. Knowing how herbicides work and act helps to define their correct way of use and, mainly, to understand the symptoms of injuries they can cause to crops, such as the use of some molecules that act directly to inhibit the synthesis of important amino acids for development. of culture. The mechanism of action is related to the first biochemical or biophysical step within the cell to be inhibited by herbicidal activity. Herbicides generally inhibit the activity of an enzyme/protein in the cell and, as a consequence, trigger a series of events that kill or inhibit the development of the cell and organism (VIDAL, 1997). Therefore, the mode of action is the final effect expressed on the plant after application of a herbicide.

Therefore, we must pay attention to the mechanism of action of some molecules that are responsible for inhibiting the synthesis of important amino acids, as in the case of glyphosate, a herbicide currently widely used in soybean, corn and cotton crops. They belong to the group of herbicides that inhibit the enzyme enol – pyruvyl – shikimate – phosphate – synthase – EPSPs – responsible for one of the steps in the synthesis of aromatic amino acids such as tryptophan, phenylalanine and tyrosine. During its metabolic process, there is a blockage in the shikimic acid route, inhibiting the synthesis of aromatic amino acids that are directly linked to the development of roots and plant defense compounds such as lignin, tannin and phytoalexins. In addition to EPSP inhibitors, we also have ALS inhibitors – Acetolactate synthase and GS – Glutamine synthase, these are molecules widely used in commercial crops and which act directly on the synthesis of some amino acids, interrupting important physiological processes in plants. Among the group of ALS inhibitors widely used in commercial crops, we have trifloxysulfuron-Sodium (ENVOKE) and Pyrithiobac-Sodium (STAPLE), which act by blocking the synthesis of some amino acids such as valine, leucine and isoleucine. Inhibition of ALS results in inadequate supplies of the amino acid chain, which leads to shoot growth arrest, stunting, yellowing, and roots being reduced in number and growth (ROSS; CHILDS 1996).

In the case of GS inhibitors, we have Glufusinate-ammonium salt (FINALE AND LIBERTY), which acts by inhibiting the synthesis of glutamine synthase, responsible for the reaction of ammonia formed in the cell with glutamic acid to form glutamine. Glutamic acid has important functions as a precursor of chlorophyll, helps with nitrogen metabolism and is a precursor to all other essential amino acids. Therefore, we know that the use of herbicides can cause physiological secondary effects on important metabolic processes and the verification of these effects requires the adoption of management strategies that minimize these negative impacts.

One of the ways to minimize negative impacts is through the application of isolated amino acids or in combination with other products. However, we must pay attention to the types of amino acids present on the market that we intend to apply. Not all amino acids are the same, they can be presented in both the L form (LEVOTOTARY) and the D form (DEXTROTARY), amino acids in the L form are readily available for absorption as they are already in free form, proteins are only formed by amino acids in the L form. While in the D form they are not readily available and only function as nutrients and not as amino acids and their main use ends up being the chemical industry in the production of antibiotics. The way these amino acids are obtained is what will distinguish their quality whether they are in the D or L form. Two obtaining processes are known, namely hydrolysis and fermentation. In the hydrolysis process there is a very large uncertainty as to whether the amino acids obtained are in the L or D form. In the fermentation procedure, the process is biological and only produces amino acids in the L form.

REVITA is an option for post-stress management, especially when we talk about herbicides. It is a product originating 100% from microbial fermentation, with high amounts of free amino acids readily available for rapid absorption via the leaves, with aromatic amino acids and tryptophan precursors in its composition, in addition to glutamic acid that will give rise to all other essential amino acids.