Understanding the role of amino acids and their importance for agriculture

Plants are considered sessile organisms and, therefore, cannot move, and as a survival strategy, they have developed complex mechanisms capable of dealing with the changes imposed throughout their cycle. Fluctuations in environmental conditions such as extreme temperatures, water deficiency, flooding, salinity considerably affect productivity. Additionally, the presence of pests and diseases negatively contributes to increased damage and consequently negatively influences the expression of the productive potential of crops. These effects become more aggravated in successions of crops, being subject to nutritional imbalance and susceptible to pressure imposed by pests and diseases arising from the previous crop. Faced with a challenging scenario, knowledge and understanding of plant physiology began to be considered a new strategy to assist in the search for increased productivity.

Technology in genetic improvement and advances in the molecular biology scenario, associated with research and development of products aimed at physiological stimulation of plants, provide farmers with better productivity returns. Therefore, it is vital to know the stages of crop development, as well as knowledge of the physiological mechanisms associated with plant responses to exogenous stimuli in order to maximize the maximum productive capacity of crops of economic interest.

After all, how do amino acids enhance plant development?

Amino acids are organic substances used mainly for protein synthesis. However, these organic substances are also sources of nutrients, activators of plant metabolism as well as suppliers of carbon skeletons for numerous metabolic pathways, including secondary and hormonal metabolism. They are also used as respiratory substrates under carbon deficiency (decrease in photosynthesis), contributing to the production of energy for plants in the form of Adenosine Triphosphate (ATP) (Figure 1, Batista-Silva et al., 2019).

Amino acids are directly involved in different cellular processes and their endogenous levels are regulated by complex synthesis and catabolism pathways, also influenced by protein synthesis and degradation. Although plants are capable of synthesizing amino acids to meet the most diverse physiological functions, exogenous supplementation in agricultural areas is considered an intelligent strategy to stimulate increased productivity, as well as a source of relief from water, saline, thermal or high stress. luminous intensities since the energy previously directed to maintaining the 'turnover' These organic molecules can now be used for cell maintenance and growth (Figure 1).

It is worth noting that plants require specific amounts of amino acids throughout their cycle. Therefore, knowledge of its functions is extremely important to obtain the best performance. Furthermore, it is worth highlighting that amino acids are organic substances capable of chelating cations as well as increasing the absorption and transport of different nutrients in all parts of plants. This occurs based on the speed of penetration via the cuticle, which favors the penetration of these nutrients, since the ionic charge of the metal is neutralized, supplying the plant with these nutrients efficiently.

As well as the absorption of macro and micronutrients, amino acids can be absorbed by the root system and by leaves, stems and branches. In the root system, absorption into the cells occurs via specific transporters, which are associated with the expenditure of energy for loading into the cells (Tegeder and Rentsch, 2010). The penetration of these molecules via leaves, stems and branches occurs after the two barriers in the leaf blade, such as the cuticle, and later via the membrane, are broken. In this way, around 25% of the amino acids applied to plants, after one day, are already incorporated into plant metabolism as if they were synthesized by the plant and already contribute to the growth and development process (Stiegler et al., 2008; Tegeder and Rentsh , 2010).

Amino acids as stress relievers are explained by the fact that specific groups of amino acids are used directly in the mitochondria during the respiratory process (Figure 1). Amino acids such as branched chain amino acids (Leucine, Isoleucine and Valine), as well as aromatic acids (Tyrosine, Tryptophan and Phenylalanine), lysine and sulfur acids such as cystine and methionine are completely oxidized, releasing electrons directly into the electron transport chain, contributing to the energy synthesis in the form of ATP - adenosine triphosphate molecule and nutrient sources such as sulfur (Figure 1, Araújo et al., 2011; Hildebrandt, 2018). These processes are commonly triggered when stresses induce photosynthetic limitation and reductions in carbohydrate levels, an energy source, directly affecting the growth and accumulation of biomass in the form of leaves or reproductive organs such as grains, fruits, roots, etc.

Furthermore, studies have shown that the exogenous application of amino acids increases plant tolerance to various abiotic stresses (water, thermal, light and others) and, in their set of functions, amino acids guarantee excellence in physiological processes (Figure 1) . Also, these applications modulate cellular hormonal levels, since tryptophan and methionine are precursors of the hormones auxin and ethylene, respectively (Taiz & Zeiger, 2010). In this way, the absorption of these hormones will induce root formation and improve plant establishment. Additionally, auxin increases the maintenance of the shoot apical meristem, generating new vegetative and reproductive structures (Figure 1). The application of amino acids increases the entry of carbon into the plant system, accelerating the recovery of the harmful effects caused by the use of herbicides (glyphosate) by enabling the conversion of photoassimilates and functional structures.

The class of aromatic amino acids provides protection against attacks by pests and pathogens, as they are also part of the synthesis pathway of several compounds present in secondary metabolism, such as phenolic groups (cinnamic acid, caffeic acid, flavones and coumaric acids) and which are often used as plant defense compounds (Figure 1). Furthermore, they are important in post-formed physical responses such as the participation in lignin synthesis in plants.

Amino acids, therefore, provide more balanced production systems, since they are closely related to the excellence of the metabolism of cultivated plants. In this scenario, Kimberlit Agrociências makes the use of amino acids in agriculture tangible through the supply of high quality liquid and solid fertilizers that are additives with an exclusive composition of amino acids.

By Bruno Neves Ribeiro MSc. Agricultural Engineer, Research & Development Coordinator and Willian Batista-Silva DSc. Agricultural Engineer, Research & Development Analyst, at Kimberlit Agrociências