Plant growth regulators are a class of substances with similar physiological and biochemical effects to plant hormones. Plant growth regulators cause local or short-term fluctuations in cell exchange or electrolyte exchange in plants by stimulating, inhibiting or blocking hormone receptors, and increase or decrease the state of a certain hormone in plants. Plant growth regulators can not only increase crop yields, but also enhance stress resistance and improve quality, playing a major role in extending product storage life and the development of crop breeding.
- Types of plant growth regulators
There are about 40 active ingredients in plant growth regulators, which can be used as a single ingredient or in combination. Many plant development processes can actively regulate cultivated plants, such as accelerating or delaying seed germination, breaking plant dormancy, stimulating or reducing stem elongation, inducing flowering and fruiting, reducing or increasing fruit yield, and accelerating or delaying the aging process (including fruit ripening and leaf fall, etc.). The benefits achieved in production include facilitating crop management, increasing and ensuring the yield and quality of harvested products, and extending the storage period of crops.
According to the role of plant growth regulators in agricultural production, they can be divided into 5 categories: plant growth promoters, plant growth retardants, plant growth inhibitors, preservatives and drought resistance agents. Usually, they can spread to the site of action in the plant body. At very low concentrations, they can promote or inhibit certain links in the plant life process, so that they can play the role they need.
Growth promoters: can improve the growth efficiency of crops, and can also transform crops from vegetative growth to reproductive growth, increase fruit setting rate, and achieve increased production.
Growth retardants: The main function is to reduce the growth of new shoots, promote the formation of flower buds, improve fruit setting, delay maturity, increase hardness and storage resistance.
Growth inhibitors: can completely inhibit the growth of stem tips and have permanent inhibition on crops. Promote the transformation of crop vegetative growth to reproductive growth, reduce fruit shedding before harvest, and accelerate the maturity period.
Preservatives: have protective and therapeutic effects, inhibit the respiration and cell proliferation of pathogens. Mainly used for the treatment of fruits and vegetables after harvest.
Drought-resistant agent: Chemical covering agent can effectively prevent the evaporation of water in the soil, increase the water absorption of crop plant roots and effectively reduce plant transpiration. Water retaining agent is mainly composed of high molecular weight water-absorbing resin. Water retaining agent is mainly used for seed coating, transplanting plant root dipping, seed and seedling preservation in production, so that it can absorb moisture in the soil and air around seeds or plants. In the early stage of drought, it can ensure the germination of seeds and the survival and growth of cuttings and transplanted crops. Fulvic acid is currently the main anti-transpiration agent. Spraying before and after crop transplanting can shorten the seedling period of transplanted crops and improve the survival rate.
- Common types and functions of plant growth regulators
2.1 Auxin
Auxin can promote cell division, cell differentiation and cell growth, increase fruit setting rate, prevent fruit drop, induce the formation of adventitious roots, the formation and differentiation of the vascular system of new roots, promote the growth of taproots, and improve plant germination rate and survival rate. It enters the plant through the leaves, tender epidermis of branches, and seeds, and reaches the point of action as the nutrients flow. It is widely used in the rooting of cuttings of trees and flowers.
2.2 Gibberellic acid
Gibberellic acid has a long-lasting effect. Compared with other plant growth regulators, it is more efficient, more stable, and safer. Spraying during the seedling stage can promote root development and prevent diseases; spraying during the growth period can promote stem and leaf growth and balance nutrition; spraying during the flowering period can protect flowers and fruits, make the fruits swell, have a more beautiful fruit effect, and can also effectively eliminate crop diseases.
2.3 Aminoethyl esters
Aminoethyl esters are a broad-spectrum plant growth regulator that can promote cell division and elongation, promote the growth and differentiation of growth points; increase the chlorophyll content in plants, thereby increasing the photosynthesis rate; regulate the water balance in plants, strengthen the absorption of water and fertilizers by plants, so as to improve the drought resistance and cold resistance of plants. Promote seed germination, root development and flower bud differentiation, make plants bloom earlier, promote early maturity of crops, increase crop yield, improve crop quality, and delay plant aging.
2.4 Chlorpropamide
Chlorpropamide has the effect of affecting the development of plant buds, accelerating cell mitosis, promoting cell enlargement, differentiation and organ formation, promoting the growth of roots, stems, leaves and fruits, promoting crop fruiting, preventing the shedding of fruits and flowers, accelerating the shedding of leaves, thereby delaying the aging of late crop leaves, making the fruit size uniform, improving quality and increasing yield. It can be used as a herbicide at high concentrations.
2.5 Sodium nitrophenolate
Sodium nitrophenolate is a broad-spectrum plant growth regulator that promotes the flow of cell protoplasts, improves cell vitality, accelerates plant growth and development, promotes the growth of roots, stems, leaves and fruits, preserves flowers and fruiting, increases crop yields, and enhances crop resistance and other abilities. It has low toxicity, no residue, and is pollution-free. It can be used alone or as a fertilizer additive. It is an excellent fungicide, synergist, and fertilizer.
2.6 Ethylene
Ethylene is the simplest olefin. It exists in plants at a very low content and is a natural plant metabolite. It can break the dormancy of plant seeds and seedlings, induce the production of adventitious roots and root hairs, reduce the growth rate of plants, promote fruit ripening, promote leaf aging, inhibit plant flowering, and change the sex and differentiation direction of flowers in plants with male and female flowers in the early stages of flower development.
2.7 Cytokinin
Some cytokinins are isolated from corn or other plants, and some are artificially synthesized. Generally produced in the roots of plants, it is a type of substance that can promote cytoplasmic division and lateral elongation of cells. It can promote the differentiation and growth of various plant tissues. It has a synergistic effect with plant auxin. It also has the effects of removing apical dominance, inhibiting stem elongation, inhibiting the decomposition of chlorophyll, breaking the dormancy of plant seeds and seedlings, promoting chloroplast development, and cold resistance.
2.8 Abscisic acid
Abscisic acid is also known as abscisic acid or dormant hormone. It is named because it can promote the shedding of leaves and is widely distributed in higher plants. In addition to promoting the shedding of leaves, it can also regulate the development of seeds and embryos, causing buds to enter a dormant state, and inhibiting the extension of cells, causing the stomata of plant leaves to close, and promoting the formation of tubers in potatoes. In addition, it can also increase the stress resistance of plants and has the function of defending against salt damage, heat damage, and cold damage.
2.9 2,4-D
2,4-D promotes plant growth at low concentrations, prevents flowers and fruits from falling, and induces parthenocarpy. Treating tomato flowers with a low concentration of 2,4-D aqueous solution can prevent flowers and fruits from falling, form seedless fruits, and promote fruit growth. High concentrations of 2,4-D can be used for thinning flowers and fruits, preventing weeds, etc.
2.10 Naphthaleneacetic acid
Naphthaleneacetic acid has the effect of promoting rooting of cuttings, preventing shedding and parthenocarpy. If the current year’s green leaf cuttings are soaked in NAA solution of appropriate concentration, the rooting rate can be significantly improved. In addition, naphthaleneacetic acid also has the effects of improving the survival rate of transplantation and promoting graft healing.
2.11 Plastic
Plastic is an antibiotic that can inhibit cell mitosis, inhibit top growth, promote axillary bud growth, dwarf plants, inhibit seed germination, and is also often used to shape dwarf tree bonsai.
2.12 Maleic hydrazide
The commercial name of maleic hydrazide is qingxiansu. It has the opposite effect of auxin and can inhibit bud germination and stem elongation, so that plants end growth early, promote maturity, and prolong dormancy. It is often used to prevent premature germination of potatoes, onions, and garlic.
2.13 Chlormequat
Chlormequat has the opposite effect of gibberellins and inhibits the elongation of many plants. It is mainly used for barley, wheat and rice to make plants short and strong and reduce lodging. Chlormequat is also used to inhibit the excessive growth of cotton branches and improve plant shape to increase yield.
2.14 Metcholine Chloride
The effect of Metcholine Chloride in inhibiting growth is similar to that of Chlormequat, but the efficacy is longer. It is used to prevent wheat from lodging and inhibit the excessive growth of cotton branches and the shedding of buds and bolls.
2.15 Biju
The physiological effect of Biju is to weaken vegetative growth, inhibit the germination of new shoots, and accumulate assimilated products. It is conducive to flower bud differentiation. In peanut cultivation, lodging often occurs due to excessive growth, resulting in reduced yield. During the period when stems and leaves grow most vigorously, spraying the leaves with Biju solution can make the plant short and compact, the leaf color deepens, and the leaves thicken, which promotes the transportation of more photosynthetic products to the fruiting organs in the underground part and increases peanut yield.
2.16 Paclobutrazol
Paclobutrazol is an inhibitor of GA. The main function of paclobutrazol is to dwarf the plant and promote lateral growth, thicken the stem, straighten the leaves, increase tillers or branches, and make the young trees bloom earlier and produce more early.
2.17 Ethephon
When the pH value is >4.1, ethephon decomposes and releases ethylene. The function of ethephon is the same as that of ethylene. It has the functions of promoting fruit ripening, inducing the formation of female flowers in cucumbers, and stimulating the discharge of secondary metabolites.
It is worth noting that the use of the dosage, period and method indicated on the registration and approval label of plant growth regulators generally does not cause harm to human health. However, in actual production, if the drug is not used in a standardized manner, it will lead to excessive growth of crops, or inhibit growth, or even cause crop death, and even have a certain impact on the quality of agricultural products and human health.
