October 14, 2020
How are L-Amino Acids and D-Amino Acids Different in Plants?
Amino acids are the basic building blocks of all life forms. They are organic molecules that can form a diverse range of proteins. There are 500 different amino acids in nature. These are essential amino acids and needed for life. Humans can’t synthesize all types of amino acids on their own. Unlike humans, plants can synthesize all amino acids they need by themselves, but plants can be deficient in amino acids, which can alter growth and decrease crop production. Amino acids are within the structure of a plant, so applying amino acids to a plant directly can substantially improve the health and growth of a plant. So, it is best to know what the different amino acids are, some of which include L-amino acids and D-amino acids.
Difference Between L-Amino Acids and D-Amino Acids in Plants
Not all amino acids are exactly similar. Amino acids occur in two isomeric L- and D- forms. The difference between L-amino acids and D-amino acids is based on their left and right-handed configurations around the central carbon atom. Both forms are mirror images of each other, this is called chirality and the central carbon atom is termed as the chiral center. The most commonly occurring or the major form of amino acids in plants is the L-form while d-form is comparatively rare. The L-form is more extensively researched. L-amino acids perform several vital functions in plants, while, the d-form has a limited role in plant physiology and yet to be studied in detail.
L-Amino Acids in Plants and their Functions
Naturally, the only type of amino acids plants can utilize with very rare exceptions are L-amino acids (left turning forms). L-amino acids are the primary basis of plant life. They are synthesized by a process called “enzymatic hydrolysis”.
- Feeding plants with L-amino acids provides them more energy to carry out several important physiological processes in plants.
- L-amino acids can perform a myriad of vital functions in plants and scientists are continuously working on discovering more of them.
The effect of L-amino acids on plant growth is known as ‘biostimulation’. Biostimulation is simply the process of plant grown stimulation. Plants need much more than the basic 16 to 17 mineral elements for their normal physiological activity. Several important processes in plants are carried out by L-amino acids such as reproduction, several hormonal and enzymatic processes, structure building, immunity, and nutrient translocation. Feeding plants with L-amino acids enables them to perform these functions more efficiently thereby promoting healthier growth of plants.
Supply of Organic Nitrogen
Most of the synthetic fertilizers contain high quantities of nitrogen in the form of nitrates and ammonium. Both these forms are utilized by the plants for their normal functioning. However, there remains a less discussed source of nitrogen due to the lack of extensive research evidence. L-amino acids also contain nitrogen and release nitrogen inside the plants that is utilized by them. The nitrogen taken up by plants is utilized in the formation of protein and amino acids. If the plants are fed with a bioavailable form of nitrogen, they will require fewer nitrates and ammonium molecules. The supply of nitrogen through bioavailable forms will help to avoid the overdose of nitrogen that can cause several problems in plants. The excess of nitrogen is not safe to the plants, it promotes faster growth that can ultimately lead to cell elongation and the cells walls of rapidly growing cells become thin and stretched. This weakens the whole plant and makes it an easy target for several detrimental pests and diseases. Another disadvantage of excess nitrates is that they can interact with other minerals in the soil causing mineral deficiencies. When nitrogen is provided in a balanced amount, plants will grow healthier and sturdier with better ability to resist the attack of pests and diseases.
L-amino acids provide nitrogen to the plants. Two forms of L-amino acids i.e., Glycine and L-glutamic acid are essential for chlorophyll formation. These amino acids increase the concentration of chlorophyll in plants. More chlorophyll causes more absorption of light which enhances the rate of photosynthesis. The increase in the rate of photosynthesis provides more food to the plants in the form of carbohydrates that ultimately improves plant health.
The most promising role performed by L-amino acids is the bioavailability of essential nutrients. There are certain nutrients that are not readily absorbed by plants due to their ionic charge and structural arrangements. L-amino acids possess the ability to pack these available minerals so the plants can easily absorb and translocate them. This process of packing minerals is known as mineral chelation.
L-Glutamic acid and Glycine are two forms of L-amino acids that are very effective chelating agents due to their low molecular weight. Their small size enables them to pass through cell membranes easily.
In addition to increasing the availability of minerals, L-amino acids can also decrease the metal toxicity in plants and soil by binding with excess metals.
Precursors to Plant Hormones and Growth Factors
L-amino acids also act as precursors of several plant hormones and important growth-related compounds.
- L-methionine acts as a precursor of ethylene (Ethylene is vital for flower formation and fruit ripening)
- L-tryptophan is a precursor of Indole-3-Acetic acid production (Indole-3-Acetic acid is required for root growth)
- L-tryptophan is also a precursor of auxin formation (Auxin is required for plant development processes)
- Cytokinin synthesis is initiated by L-arginine (Cytokinin promotes cell division or cytokinesis in plants)
Pollination and Fruit Formation
L-amino acids are extensively utilized during peak metabolic functioning of plants. They play an important role in pollination and fruit development.
- L-Histidine is essential for fruit ripening
- L-Lysine, L-Glutamic acid, and L-Methionine increase the germination of pollen and the length of the pollen tube
- L-Proline enhances pollen fertility
- L-Alanine, L-Leucine, and L-Valine improve fruit quality
D-Amino Acids in Plants and their Functions
There has been scarce information about D-amino acids in plants for a long time but recently there have been some advances in this field. Plants take up D-amino acids mainly from the soil, but they can also be synthesized. The fact that plants obtain D-amino acids from the soil in their surrounding environment raises the question, what are the functions of these D-amino acids in the plant system?
The occurrence of D-amino acids in plants indicates that these molecules play some important roles in plant physiology. However, their functions in plants are poorly researched and many of these functions are yet to be understood. There are a few important functions of D-amino acids in plants that will be discussed below.
Are D-Amino Acids Inhibitory or Growth-Promoting?
According to several reports, D-amino acids have an inhibitory effect on seedling growth. However, there is also increasing evidence for the growth-promoting effect of D-amino acids. In a recent study, it has been discovered that the exogenous application of several D-amino acids enhances the growth of pepper plants. The growth-promoting effect of D-amino acids has been associated with the increased availability of nitrogen. There is evidence that D-amino acids can also be a source of organic nitrogen to the plants.
Regulation of Pollen Growth
D-amino acids are found to be involved in pollen growth regulation. They act as signaling molecules in plants for pollen development. D-serine is an important form of D-amino acids that was reported to impact pollen tube growth in Arabidopsis plants.
Another recently discovered function of D-amino acids is their involvement in stress signaling. Duckweeds were found to accumulate D-amino acids as a response to UV-light exposure. However, this function lacks significant evidence and has to be further analyzed.
Component of Chloroplast membrane
Another novel function of D-amino acids was revealed by the analysis of the chloroplast membrane structure of mosses. It has been discovered that the chloroplast membrane of moss P. patens contains D-amino acids and constitutes a major structural component of chloroplast membranes.
All these functions of D-amino acids in plant systems are very poorly understood with scarce shreds of evidence and yet to be discussed in detail, which is why Opulent Blends only uses L-amino acids.