What types of plant growth regulators are there?
What should be noted when using plant growth regulators on vegetables? I would like to ask for advice. The use of plant growth regulators on vegetables is already very widespread and has brought considerable benefits to vegetable growers, but some vegetable growers rely too heavily on plant growth regulators, arbitrarily increasing the dosage and raising the concentration, causing phytotoxicity and unnecessary losses. To avoid...
What plant growth regulators are there? What are their effects?Below are several common plant growth regulators and their properties:
1. Indoleacetic acid (IAA)
Molecular formula: C10H9NO2
Molecular weight: 162.0
Properties: The pure product is colorless, oxidizes to rose red when exposed to light, and its activity decreases. It should be stored in a brown bottle or shielded from light with black paper outside the bottle. Melting point 166-168°C, slightly soluble in water, benzene and chloroform, easily soluble in ethanol, ether, acetone and ethyl acetate. It is unstable in acidic media; when pH is below 2, it will quickly lose activity even at room temperature. Indoleacetic acid is relatively stable in alkaline solution, and its sodium and potassium salts are easily soluble in water and relatively stable. If an aqueous solution of indoleacetic acid is exposed to light, it will be decomposed and destroyed, so this issue should be noted in practice.
Toxicity: Acute percutaneous LD50 in mice is 1000 mg/kg. Intraperitoneal injection LD50 in mice is 150 mg/kg.
Carp LC50 (48 hours) >40 ppm. Non-toxic to bees.
Mechanism of action: IAA is obtained by biochemical methods from plant stem tips and growing leaves
Application: Indoleacetic acid (IAA) is a broad-spectrum plant growth regulator of the indole class with auxin activity. At present it is mainly used in plant tissue culture, inducing callus formation, and promoting rooting of cuttings of herbaceous and woody ornamental plants.
IAA was first isolated by F. Kerr of the Netherlands in 1934 from yeast in culture medium. Similar compounds such as 3-indoleacetaldehyde were found in plants. In the same year, King chemically synthesized indoleacetic acid.
2. Indolebutyric acid (IBA)
Molecular formula: C12H13NO2
Molecular weight: 203.23
Properties: White or slightly yellow crystalline powder, with a slight peculiar odor, melting point 123-125°C. Insoluble in water and chloroform, soluble in organic solvents such as ethanol, ether and acetone. It is a highly efficient growth regulating substance.
Toxicity: Intraperitoneal injection LD50 in mice (median lethal dose per kg body weight) is 100 mg/kg, low toxicity to humans and livestock.
Application: Mainly used to promote rooting of cuttings, with relatively strong action and a longer duration; the adventitious roots induced are numerous, slender and long.
3. Naphthaleneacetic acid (NAA)
Molecular formula: C12H10O2
Molecular weight: 186.21
Properties: The pure product is colorless, odorless needle-like crystals. It is stable in nature but easily deliquescent and changes color when exposed to light, so it should be stored away from light. Naphthaleneacetic acid is divided into α-type and β-type; the α-type has stronger activity than the β-type, and what is usually called naphthaleneacetic acid refers to the α-type. Melting point 134.5-135.5°C. Insoluble in water, slightly soluble in hot water, easily soluble in ethanol, ether, acetone, benzene, acetic acid and chloroform. The sodium salt of naphthaleneacetic acid is soluble in water and stable in general organic solvents.
Toxicity: Non-toxic to humans and livestock. Oral LD50 in rats is 1000 mg/kg, in mice 670 mg/kg, and acute subcutaneous injection KD50 in rabbits is 5000 mg/kg.
Uses: Promote plant growth, rooting of cuttings, flower and fruit thinning, prevent flower and fruit drop, promote flowering, inhibit sprouting, promote early maturity and increase yield.
4. 2,4-Dichlorophenoxyacetic acid (2,4-D)
Chemical name: 2,4-dichlorophenoxyacetic acid
Properties: The pure product is white crystals, odorless and tasteless, non-hygroscopic, melting point 141°C. The industrial product is white or light brown crystals with a slight phenolic odor, melting point 135-138°C, sparingly soluble in water, with solubility of 540×10-6 at 20°C and 890×10-6 at 25°C. It can dissolve in ethanol, ether, acetone and benzene, etc., and is stable in nature under normal temperature conditions. 2,4-D itself is a strong acid and is corrosive to metals. It reacts with various alkalis to form corresponding salts, which are easily soluble in water after salt formation. With alcohols under sulfuric acid catalysis, it forms corresponding esters, which are insoluble in water. Exposure to ultraviolet light causes partial decomposition. 2,4-D has the strongest activity among phenoxy compounds, 100 times greater than indolebutyric acid.
Toxicity: Oral LD50 in rats is 500 mg/kg.
Uses: The uses of 2,4-D vary with concentration, and the effects differ. At lower concentrations (0.5×10-6-1.0×10-6), it is one of the medium components in plant tissue culture; at medium concentrations (1-25×10-6), it can prevent flower and fruit drop, induce seedless fruit formation and preserve fruit freshness, etc.; at high concentrations (1000×10-6), it can kill many broadleaf weeds.
6. Gibberellin
Molecular formula: C19H22O6
Molecular weight: 246.39
Properties: The pure product is white crystals, and the industrial product is a white powder. Melting point 233-237°C. Easily soluble in organic solvents such as alcohols, acetone, ethyl acetate and glacial acetic acid, sparingly soluble in water, and insoluble in petroleum ether, benzene and chloroform, etc. When using gibberellin original powder, first dissolve it with a small amount of ethanol or liquor, then add water to the required concentration. Its stability differs in different pH solutions: under pH 3-4, its aqueous solution is most stable; under neutral or slightly alkaline conditions, stability decreases markedly; in alkaline solution it is neutralized and becomes ineffective, so it must not be mixed with alkaline pesticides (such as lime sulfur mixture) in application. Gibberellin solution gradually loses activity when it exceeds 50°C, and will lose activity after long-term storage at room temperature or high temperature.
Toxicity: Non-toxic to humans and livestock. Oral administration of 1500 mg/kg in mice did not cause poisoning.
Application: Promote stem elongation and leaf expansion; break dormancy, promote germination, and increase seed germination rate; promote fruit set in some plants; promote the formation of male flowers in both sexes, and inhibit flower bud differentiation in fruit trees; replace low-temperature induction, etc.
7. Ethephon
Molecular formula: C2H6CLO3P
Molecular weight: 144.5
Properties: The pure product is long needle-like colorless crystals, melting point 74-75°C, easily soluble in water, ethanol and ether, slightly soluble in benzene and dichloroethane, insoluble in petroleum ether. The formulation is a brownish-yellow viscous strongly acidic liquid, specific gravity 1.2-1.3, pH about 1. It is relatively stable at room temperature and below pH 3, and almost does not release ethylene; above pH 4.0 it decomposes and releases ethylene, and the ethylene release rate accelerates with increasing temperature and pH value. Ethephon will completely decompose after being bathed in alkaline boiling water for 40 min, releasing ethylene, chloride and phosphate.
Toxicity: Acute oral LD50 in rats is 4229 mg/kg.
Application: Promote adventitious root formation, stem thickening, break dormancy, induce flowering, control sex differentiation of floral organs, make cucurbits produce more male flowers, improve ripening, ripen fruits, and promote senescence and abscission.
8. Zeatin
Properties: Zeatin has cis and trans isomers, and trans-zeatin has strong biological activity. Trans-zeatin is white needle-like crystals. Melting point 208-210°C. Soluble in water and ethylene glycol.
Application: 1. Promote callus sprouting (must be used with auxin), concentration 1 ppm. 2. Promote fruit set, zeatin 100 ppm + gibberellin 500 ppm + naphthaleneacetic acid 20 ppm, spray fruit 10, 25 and 40 days after flowering. 3. Leafy vegetables, spray at 20 ppm, can delay leaf yellowing. In addition, seed treatment of some crops can promote germination; treatment at the seedling stage has a growth-promoting effect.
9. Kinetin (KT)
Molecular formula: C10H9N5O
Molecular weight: 215.22
Properties: The pure product is a white solid, melting point 265-266°C, soluble in strong acids, alkalis and glacial acetic acid, slightly soluble in ethanol, butanol, acetone and ether, insoluble in water. When preparing, first dissolve it in a small amount of ethanol or acid, and only after complete dissolution dilute with water to the required concentration.
Uses: Kinetin is mainly used in tissue culture to promote cell division and regulate cell differentiation, delay organ senescence, and preserve freshness of fruits and vegetables.
10. 6-Benzylaminopurine (6-BA)
11. Forchlorfenuron (CPPU, KT-30)
Molecular formula: C12H10CLN3O
Molecular weight: 247.68
Properties: White crystals, melting point 171-173°C
Application: It is a phenylurea plant growth regulator with cytokinin activity, widely used in agriculture, horticulture and fruit trees to promote cell division, promote cell expansion and elongation, and promote fruit enlargement, etc.
12. Chlormequat (CCC)
Properties: The pure product is white rhombic crystals, easily soluble in water, insoluble in benzene, xylene, ethanol and ether, slightly soluble in dichloroethane and isopropanol. Stable in neutral or acidic media, less stable in alkaline media; heating with alkali will decompose and make it ineffective.
Toxicity: Oral LD50 in male rats is 670 mg/kg, in female rats 1020 mg/kg.
Application: Inhibit cell elongation without inhibiting cell division, and inhibit stem growth without inhibiting sexual organ development.
13. Daminozide (B9)
Molecular formula: C6H12N2O3
Molecular weight: 160.17
Properties: Easily soluble in water, easily decomposed by microorganisms in soil, stable within plants.
Application: Inhibit the biosynthesis of auxin and gibberellin. Make plants dwarf, leaves green and thick, enhance stress resistance, promote fruit coloration and prolong storage period.
14. Paclobutrazol PP333
Chemical name: (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-3-pentanol
Molecular formula: C15H20N3OCL
Molecular weight: 293.5
Properties: White crystals, melting point 165-166°C. Solubility: water 35 mg/L, methanol 15%, acetone 11%, dimethyl methanol 6%. The pure product is stable for more than 6 months below 25°C, and dilute solutions are stable at any pH value and stable to light.
Toxicity: Low toxicity to mammals. Acute oral LD50 in rats is 1500 mg/kg, acute subcutaneous injection LD50 is 1100 mg/kg. Slight skin irritation in rats, moderately toxic to rabbits, and low toxicity to birds, fish and invertebrates.
Application: Delay plant stem elongation and branch and leaf expansion, inhibit cell elongation, and has fungicidal action.
15. Mepiquat chloride
Molecular formula: C7H18CLN
Molecular weight: 149.7
Properties: The pure product is white crystals, soluble in water, insoluble in organic solvents. Inhibits the biosynthesis of gibberellin.
Application: Make plants dwarf, improve assimilation capacity, promote maturity, increase yield; easily decomposes in soil, and foliar spraying works well.
16. Abscisic acid (ABA)
Molecular formula: C15H20O4
Molecular weight: 264.3
Properties: Sparingly soluble in water, benzene and volatile oils. Soluble in methanol, ethanol, acetone, ethyl acetate, etc., and also soluble in sodium bicarbonate solution.
17. Maleic hydrazide (MH)
Molecular formula: C4H4N2O2
Molecular weight: 112.09
Properties: White crystals, melting point >296°C
Application: Can be used to inhibit the growth of lawns, hedges and trees, inhibit sprouting of carrots, sugar beets, potatoes, onions and cabbage, and inhibit tobacco axillary bud growth. Mixed with 2,4-D, it can also control weeds.
18. Triiodobenzoic acid
Molecular formula: C7H2O2I3
Molecular weight: 500.92
Properties: Insoluble in water, easily soluble in ethanol, ether, benzene, toluene, etc. It can hinder the transport of auxin within the plant.
Uses: Inhibit apical growth of stems, promote axillary bud germination, make plants branch more, and increase the number of flowers and fruit set.
19. Triacontanol
Molecular formula: C30H62O
Molecular weight: 438
Properties: Insoluble in water, soluble in ether, chloroform and dichloromethane. It can be formulated into an emulsifiable concentrate with chloroform and Tween 20 (or 80) for use. Stable to light, air, heat and alkali. The efficacy is related to the purity and particle fineness of the product. After adding calcium chloride (10-3 MOL/L), the effect is significant and stable.
Uses: Promote photosynthesis, improve nitrogen nutrition, enhance stress resistance.
20. Brassinolide
Molecular formula: C28H48O6
Molecular weight: 480
Brassinolide (BR) OH
Properties: Melting point 274-275°C, easily soluble in water.
Uses: Promote cell division and elongation, enhance resistance, and increase seed-setting rate.
21. 4-CPA
Aliases: 4-CPA, PCPA
Chemical name: p-chlorophenoxyacetic acid
Molecular formula: C8H7CLO3
Molecular weight: 186.59
Properties: The pure product is white crystals with a slight pungent odor, melting point 157-158°C, slightly soluble in organic solvents such as alcohol and ether, soluble in hot water, and stable in nature.
Toxicity: Low toxicity to humans and livestock. Acute oral LD50 in rats is 2000 mg/kg, and acute oral toxicity in mice is 1960 mg/kg.
Uses: P-chlorophenoxyacetic acid is a phenoxy plant growth regulator with auxin activity, absorbed by the roots, stems, leaves, flowers and fruits of plants. It prevents flower and fruit drop in solanaceous vegetables such as tomatoes, inhibits rooting in legumes, promotes fruit development, forms seedless fruits, advances ripening, increases yield, and improves quality, etc.
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