Proteins are the fundamental building blocks of life, and amino acids are the basic units of proteins. Indispensable for plants, humans, and animals alike, amino acids not only serve as the primary nutrients for protein synthesis but also exhibit functional properties, directly participating in various physiological activities and hormone synthesis in both organisms.
What Are Amino Acids?
Amino acids are a class of organic compounds containing both amino and carboxyl groups. As the basic units of proteins and the foundation of all life, they are the “building blocks” for constructing the biological structure of plants—also living organisms.
Since the 20th century, scientific research on amino acids has primarily focused on human and animal nutrition, overlooking their crucial role in plant nutrition. However, with the development of plant physiology in recent decades, the significant functions of amino acids in plants have been increasingly recognized.
Which Amino Acids Can Plants Absorb and Utilize?
Scientists have identified two configurations of amino acids: L-amino acids (levorotatory) and D-amino acids (dextrorotatory). L-amino acids are mirror images of D-amino acids, similar to how a left hand mirrors a right hand.
Animals and plants can only utilize L-amino acids, while D-amino acids are exclusively used by certain bacteria and fungi. Thus, only L-amino acids possess biological activity and can be absorbed by plants and animals.
Physiological Effects of 18 Amino Acids on Plants
| Amino Acid | English Name | Key Physiological Effects on Plants |
|---|---|---|
| 丙氨酸 | Alanine | Enhances chlorophyll synthesis, regulates leaf stomatal function, and resists pathogen invasion. |
| 精氨酸 | Arginine | Promotes root growth and improves plant salt tolerance. |
| 天门冬氨酸 | Aspartate | Accelerates seed germination and protein synthesis; provides sufficient nitrogen during rapid growth stages. |
| 半胱氨酸 | Cysteine | Exerts antioxidant effects and maintains normal cell function. |
| 谷氨酸 | Glutamate | Reduces nitrate content in crops; promotes seed germination, leaf photosynthesis, and chlorophyll synthesis. |
| 甘氨酸 | Glycine | Strengthens photosynthesis, favors plant growth, increases sugar content; acts as a natural metal chelating agent. |
| 组氨酸 | Histidine | Regulates leaf stomatal function, resists pathogen invasion, and promotes cytokinin synthesis. |
| 异亮氨酸、亮氨酸 | Isoleucine & Leucine | Improves salt tolerance, enhances pollen viability and aroma, and promotes germination. |
| 赖氨酸 | Lysine | Enhances chlorophyll synthesis and boosts plant cold and drought resistance. |
| 蛋氨酸 | Methionine | Promotes synthesis of plant endogenous hormones (ethylene) and polyamines. |
| 苯丙氨酸 | Phenylalanine | Facilitates synthesis of lignin and anthocyanins. |
| 脯氨酸 | Proline | Improves plant resistance to osmotic stress and enhances pollen viability. |
| 丝氨酸 | Serine | Participates in cell differentiation and promotes germination. |
| 苏氨酸 | Threonine | Enhances plant stress tolerance, reduces pest infestation, and improves humification processes. |
| 色氨酸 | Tryptophan | Promotes synthesis of endogenous auxin (indoleacetic acid) and improves synthesis of aromatic compounds. |
| 酪氨酸 | Tyrosine | Strengthens drought resistance, enhances pollen viability, and promotes germination. |
| 缬氨酸 | Valine | Increases seed germination rate and improves crop flavor. |
Note: Select amino acids based on specific growth goals in agricultural practices.
Production Processes of Amino Acids
Different production methods significantly impact the efficacy of amino acids. Common techniques include chemical synthesis, enzymatic hydrolysis, microbial fermentation, and hydrolysis. In agriculture, hydrolysis and enzymatic hydrolysis are the primary methods.
Acid/Alkali Hydrolysis
- Advantages: Low production cost and simple process. Raw materials are hydrolyzed with hydrochloric acid, sulfuric acid, or sodium hydroxide, followed by neutralization and concentration.
- Disadvantages: Destroys L-amino acids and leaves high residual chloride or sodium ions. Tryptophan and hydroxyamino acids (serine, threonine) are easily decomposed during acid hydrolysis; arginine is lost via deamination during alkali hydrolysis. Bioactive substances such as nucleotides and peptides are mostly destroyed (used by some low-cost products on the market).
Enzymatic Hydrolysis
- Advantages: Preserves a comprehensive range of amino acids, protects plant-absorbable L-amino acids, and yields high levels of oligopeptides with minimal harmful substances—making it the most suitable method for agricultural applications.
- Advanced technologies enable targeted cleavage to obtain desired molecular weight ranges (e.g., oligopeptides <1000 Daltons, which are more readily absorbed by crops), though this requires sophisticated equipment.
Plant-Derived vs. Animal-Derived Amino Acids
Proteins are classified into plant-based and animal-based, and their decomposition produces plant-derived and animal-derived amino acids, respectively. A common debate arises: which type is better?
In reality, neither is inherently superior—the question is analogous to asking whether meat, fish, or soybeans are better for humans. A balanced diet is essential for human health because different foods contain varying proportions of amino acids; no single food can provide all 20 essential amino acids in optimal ratios. The same applies to plants: amino acids from different sources have distinct compositions, leading to varying physiological effects on crops.
Humans digest proteins through chewing, stomach acid, and pancreatic enzymes, breaking them down into polypeptides, oligopeptides, and free amino acids for absorption. Plants lack this digestive capacity, so amino acids must be artificially decomposed and supplied via foliar spraying or root application. While plants can synthesize their own amino acids, adverse conditions (e.g., extreme weather, pests, diseases, pesticide damage) may limit or weaken this synthesis. Exogenous amino acid supplements help regulate plant physiological balance and optimize growth—this is the core purpose of using amino acid-based biostimulants.
Common Sources
- Plant-derived amino acids: Soybean, wheat, oats, corn, etc.
- Animal-derived amino acids: Animal hair (feathers, bristles), silkworm pupae, blood, viscera, skin, bones, and low-value fish.
Even within the same category, amino acid ratios vary. For example:
- Hydrolyzed animal hair is rich in cystine and serine.
- Hydrolyzed animal skin/bones are high in glycine and proline.
- Animal blood is abundant in leucine and phenylalanine.
- Corn and wheat are rich in glutamate.
Targeted Application
- Stress resistance: Animal skin/bone-derived amino acids (high glycine, proline).
- Lignification, shoot control, or anthocyanin enhancement: Animal blood-derived amino acids (high phenylalanine).
- Leaf greening and growth promotion: Plant-derived amino acids from corn/wheat (high glutamate).
By fully understanding the roles of amino acids in plant growth, we can develop and apply them more targeted, driving greater progress in modern agriculture!
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