What are the stresses for plants
Drought, high temperature, low temperature, salinity, heavy metals, pests and diseases. Plants often experience various abiotic and biotic stresses during the process of growth and development. Through long-term evolution and adaptation processes, plants can adopt different ways to resist various stress factors under different environmental conditions and form the ability to adapt to certain adversities. Such ability to resist various stress (adversity) factors is called stress resistance of plants.
There are two categories of stress encountered by plants: biotic stress and abiotic stress. Bacteria, fungi, viruses, insect pests, and so on, namely biotic stress. Abiotic stress includes high salinity, drought, low temperature, low oxygen, etc.
The development of sustainable agriculture has been seriously restricted by these factors and crops may even suffer multiple stresses at the same time causing serious losses to crop production. This is a question that needs to be explored the method to enhance plant stress resistance and repair and stabilize damaged and fragile ecosystems.
Cold stress: It can be divided into cold damage and freezing damage. Some plants that originated from the tropics will suffer damage at lower temperatures, the damage to plants caused by low temperatures but above 0℃ called low-temperature injury. As for freezing injury, it refers to the damage that is caused by tissue freezing when plants suffer low-temperature stress.
Drought Stress: when the plant suffers the drought, the cells of the plant will get water loss and when it reaches a certain level, the arrangement of phospholipid molecules in the membrane is disordered, the membrane protein is destroyed, and the selective permeability of the membrane is lost.
Also, the chloroplast and mitochondrial structures were destroyed. Drought will cause the reduction of the number of thylakoid sheets and distortion of the number of the chloroplast thylakoid lamellae, reduction of the number of mitochondrial inner cristae, blurriness of the nucleus and nuclear membrane, condensed chromosomes, and the decrease of the activity of synthetic enzymes and photosynthesis.
Salt Stress: The salt damage to plants is because there is too much salt in the soil. In general, salt stress will occur when the soil salinity exceeds 0.20% to 0.25%.
There are two kinds of harmful effects of salt stress: the first one is the toxicity of salt ions to plants, will damage the plasma membrane and interfere with the metabolism; The other one is the two secondary toxic effects which caused by salt ions, namely osmotic stress and nutrient deficiency stress.
Plant Diseases: One is the infection of plants by various pathogens, and the other is the inhibition of plant growth and development.
The pathogen can secret pectinesterase, pectinase, cutinase, and cellulase to hydrolyze the cell wall of the host plant, which will result in the rupture of the plant protoplast; Moreover, the pathogen can produce toxins that will destroy the structure of the host cell and interfere the normal physiological activity of the host.
Through the degradation of marine polysaccharides, marine oligosaccharides can be obtained, with unique molecular structure and biological activity. It is an exogenous inducer and it is a new natural plant growth regulator that has a certain regulatory effect on plant growth and defense response.
Oligosaccharides are represented by chitosan oligosaccharides and alginate oligosaccharides. When the plant cells recognize the signal molecules of marine oligosaccharide, they will induce reactive oxygen species burst, cause signal molecule transduction, stimulate the related defense genes expression, induce the activity of plant defense enzymes to increase, synthesize plant stress-resistant substances, and improve the ability of plant stress-resistant.
Chitosan oligosaccharide: It has great water solubility and, a small molecular weight that can be easily absorbed. Chitosan oligosaccharides also play an important role in promoting plant growth and inducing plant stress resistance. There are numerous studies have demonstrated that chitosan oligosaccharide can improve the defense ability of crops like wheat, rape, cabbage, cucumber, and tobacco, and act as a plant stress inducer.
Chitosan oligosaccharide also can be used to control the disease of fruits and vegetables after picking. It can improve the resistance of plants to abiotic stress like drought, salt stress, etc..
Alginate oligosaccharide: It is a multifunctional oligosaccharide with a degree of polymerization of 2-20 obtained from the degradation of algin. Alginate oligosaccharide is a constituent of the cell wall of marine brown algae, accounting for 17% to 45% of the dry weight of algal cells.
Alginate oligosaccharides, like oligosaccharides from other sources, act as plant signaling molecules that participate in plant growth regulation and induce stress resistance.
2. Arbuscular Mycorrhizae
Arbuscular mycorrhizae can improve host resistance to biotic and abiotic stress and it is the most widespread plant symbiotic fungi in nature.
Mycorrhizae have a variety of functions. Firstly, it can improve nutrient absorption and increase the accumulation of osmotic regulation substances and the activity of antioxidant enzymes. Secondly, it can strengthen osmotic regulation and maintain the balance of plant endogenous hormones. Thirdly, Mycorrhizae can increase auxin synthesis, regulate carbon and nitrogen metabolism, and stimulate stress-induced gene expression. Lastly, it can also enhance the plant root system and the immobilization of mycelium itself on heavy metal elements to improve plant resistance to abiotic stress like drought, high and low temperature, heavy metals, and salinity.
Through the construction of the mycelial network, it can protect the root and form a mechanical barrier to the invasion of pathogenic fungi. It can also enhance the activity of disease resistance-related enzymes, synthesize secondary metabolites related to disease resistance, enhance the expression of disease resistance-related genes, and mycelial transmission defense. The signal can even improve the resistance of adjacent plants and enhance the ability of plants to resist pests and diseases.
There are many functions of glycine betaine stress resistance: Osmotic regulation; scavenging reactive oxygen species; maintaining the stability of biofilms; protecting photosynthetic institutions; maintaining the structure and function of macromolecular protein complexes and some enzymes, etc. Since betaine can improve the photosynthetic efficiency and total soluble sugar content of plants, external application of betaine can effectively help plants resist abiotic stress.
Moreover, the external application of betaine can increase the photosynthetic efficiency and the content of total soluble sugar that can help plants resist cold stress and freezing stress effectively. Low-temperature stress or normal temperature recovery, the external application of betaine can maintain plants a higher photosynthetic effiency.
As for salt stress, glycine betaine can protect the maize photosystem and improve CO2 assimilation which alleviates the damage. Besides, betaine can improve the photosynthetic, stomatal conductance, transpiration rate, and the activities of related antioxidant enzymes significantly in all plants to resist the salt stress environment.
4. Brassinolide
When the brassinolide enters the plant, it can not only strengthen photosynthesis, and promote growth and development, but also can protect the membrane system of the plant cell and stimulate the activity of some protective enzymes which can effectively reduce the damage to normal functions caused by harmful substances produced by plants when they under stress.
There are numerous experimental studies and field trials have proved that brassinolide can enhance the stress resistance of crops, especially for drought and low-temperature, the effect is more obvious.
In order to test the cold stress, the Dora team treated the seeds and seedlings of pepper with brassinolide. The result is that the seeds treated with brassinolide have better germination rate, germination potential, vigor index, and germination index. At the same time, the levels of antioxidant enzymes and proline were up-regulated and the content of MDA reduced.
With the various adversity stresses, the photosynthesis of plants showed a downward trend and a decrease in the assimilation products supplement. Damage like drought, cold, high temperature, salinity, and waterlogging will reduce the activity of photosynthate, and stomatal closure, resulting in the supplement of CO2 insufficient and photosynthesis reduction.
SA can increase the chlorophyll content, and photosynthetic pigment and improve the photosynthetic efficiency, thereby the stress resistance of plants got improved. SA also has many physiological functions that are important to the plants, including the ability to resist pests and disease, cold, drought, salinity, and other adversity stresses.
When the plant suffers a drought, it will regulate the content or increase the activity of various antioxidant enzymes in the body. And salicylic acid can promote the effect on such a response. From the trial of the Dora team, the soaked corn seeds with a low concentration of salicylic acid had a significant increase in germination rate, germination index, and vigor index when they were under drought stress.
Under salt stress, the germination rate and chlorophyll content of mung bean seedlings could be increased by soaking seeds with SA, and the contents of MDA and proline in seedlings could be decreased, so as to maintain the integrity of the membrane. It can effectively alleviate the inhibition effect of salt stress on germination and growth of mung bean seeds, and induce the improvement of salt tolerance.
Drought, high salinity, low temperature, plant disease, and insect disease, S-ABA have an important role in plants when response to these stress. When a plant suffers adversity, it will start the system of abscisic acid synthesis and synthesize a large amount of abscisic acid. It inhibits stomatal opening, promotes water absorption, and reduces water transport routes. It can induce the synthesis of specific drought-resistant proteins and improve the stress resistance of crops.
Under drought stress, S-ABA can reduce the leaf water evaporation effectively and reduce the permeability of the leaf cell membrane. Induces the biofilm system to protect the information of enzyme SOD. Also, it will inhibit the openness of leaf stomata or even close the stomata, thereby reducing the water transpiration and improving the water retention capacity and drought tolerance of plants finally.
7. Silicon Fertilizer
When the silicon enters the plant, it can form cutin (silicon double-layer structure) in the epidermal tissue below the cuticle of the leaf. It can inhibit transpiration, reduce the evaporation of water, and improve the efficiency of photosynthesis and water utilization of the plant.
Through the deposition of silicon between the cell wall and the cuticle, it can reduce water loss and reduce wilting caused by excessive water loss under strong light. Therefore, the water utilization of the plant can be improved and the drought resistance of crops be increased.
There are numerous parasitic fungi infiltrate their hosts through the epidermal cell wall. Solid silicon combined with the cell walls of plants creates a physical barrier to prevent the infiltration of fungal hyphae and insect mandibles or larvae. Besides, the cells can not be decomposed by enzymes easily, thereby preventing the invasion of fungal hyphae along with the enzymatic hydrolysis.
Through our experiments, we came get the conclusion that silicon can improve the resistance of rice to rice blast, brown spot, and borer. Silicon deposits on the outer epidermis of plant cell walls form a physical barrier that plays an important role in plant disease resistance and insect resistance.
Jasmonic acids can regulate the process of plant growth and development and the ability of plant dwarf to adapt to the environment, it is similar to polypeptide signal molecules. When the plant faces various adverse environments, jasmonic acids can successfully participate in the stress response. Moreover, when the plant suffers threats, jasmonic acids contribute to the expression of stress resistance genes in the plant and transmit the relevant information to other parts of the plant to achieve the establishment of system stress resistance.
When the plants are under low-temperature stress, jasmonic acid treatment can improve the activity of SOD, POD, CAT, and other antioxidant enzymes in wheat seedling cells, increase the content of soluble protein, and reduce the relative conductivity and MDA content. In this way, the integrity of the cytoplasmic membrane can be maintained, and the ability of low-temperature stress resistance of wheat can be enhanced.
9. Proline
Proline plays a role in protecting plants from osmotic stress, and it is produced by plant cell accumulation when they are under stress. There are five roles proline plays in plant stress resistance.
9.1. Cytoplasmic Osmotic Regulators: When the plant cells are under osmotic stress, proline, as an osmotic regulator, transports itself into the cytoplasm, and reduces the osmotic potential by increasing the cytoplasmic concentration, thereby maintaining the osmotic balance between cells and the external environment.
9.2. Cell Structure Protector: Among all the amino acids, proline is the most water-soluble one and has a strong hydration ability. When plants are damaged, proline interacts with proteins to stabilize and protect biological macromolecules and cell membrane structures.
9.3. Free-radical Scavenger: Proline is also a scavenger of various free radicals.
9.4. Involved in Nitrogen Metabolism and Energy Metabolism: When the plant is suffering the drought, the protein of the plant will be decomposed and produce a large amount of NH3. Excessive NH3 will cause plant poisoning. Therefore, plants can translate the excessive NH3 into other forms and store it. When the plant recovers, these NH3 can be re-used after the adversity is relieved.
9.5. Adversity Stress Signal Substances: Proline is a kind of signaling molecule, that can activate different responses related to adversity adaption and its metabolic intermediates can induce the expression of resistance genes.
There are more and more biostimulant formulations that contain anti-stress materials that are welcomed by the market. They can not only improve the quality and yield of the crops but also help farmers to resist unknown risks. If you have any problems with plant stress resistance, please contact our team.