What types of plant growth regulators are there? Understanding the classification in one article

Regulators are actually a type of pesticide, and like insecticides and fungicides, they are a category of pesticide. Plant growth regulators are substances synthesized by artificially mimicking the chemical structure of plant hormones (or extracted from microorganisms) that have plant hormone activity. They are extremely widely used in agriculture, with a broad scope of action and many application fields, and they require small amounts, act quickly, deliver high benefits and leave little toxic residue. So what regulators are there?

1. Auxins (IAA)

Auxins are a class of endogenous hormones containing an unsaturated aromatic ring and an acetic acid side chain. The internationally common ones are indoleacetic acid (IAA), 4-chloro-IAA, 5-hydroxy-IAA, naphthaleneacetic acid (NAA), indolebutyric acid and others as auxin-like substances. Thus indoleacetic acid is habitually often used as a synonym for auxin.

Indoleacetic acid (IAA): Indoleacetic acid (IAA) exists in plants and can also be synthesized artificially. It is easily oxidized in light, reducing its activity, and is easily decomposed in the body by IAA oxidase.

Naphthaleneacetic acid and its homologues: Their main effects are rooting of cuttings, flower and fruit thinning, promoting flower bud formation, preventing pre-harvest fruit drop, and controlling the occurrence of sprouting shoots.

Phenol compounds: Mainly 2,4-D; 2,4,5-T; 2,4,5-trichlorophenoxypropionic acid (2,4,5-TP); 4-CPA, PCPA, fruit-setting agent; sodium nitrophenolate. Their main effects are promoting rooting, inhibiting new shoot growth, improving fruit set, etc.

2. Gibberellins (GAs)

At present there are more than 100 GA isomers, denoted as GAs. The commonly used ones are GA3 (920) and GA4+7. Their effects are breaking seed dormancy, promoting seedling growth (dormant seedlings); inhibiting flower bud formation; increasing fruit set rate, inducing parthenocarpy; promoting the enlargement of seedless grapes; and changing fruit shape.

3. Cytokinins (CTK)

Cytokinins (CTK) are a class of plant hormones that promote cell division, induce bud formation and promote its growth. The commonly used ones are ZT, BA, CPPU, TDZ. In 1955, Skoog and others in the United States, while studying plant tissue culture, discovered a substance that promotes cell division and named it kinetin.

4. Abscisic acid (ABA)

Abscisic acid is one of the natural plant growth regulators. Both the naturally active abscisic acid (+)-ABA and abscisic acid produced by traditional chemical synthesis methods are extremely costly. The physiological effects of abscisic acid are mainly causing dormancy and promoting abscission. The effects of abscisic acid are also opposite to those of cytokinins; abscisic acid in plants has both an antagonistic effect on gibberellins and an antagonistic effect on cytokinins.

5. Ethylene (ETH)

Ethylene is a plant endogenous hormone. All parts of higher plants, such as leaves, stems, roots, flowers, fruits, tubers, seeds and seedlings, will produce ethylene under certain conditions. It is converted from methionine under conditions of sufficient oxygen supply. It is the smallest molecule among plant hormones, and its physiological functions are mainly promoting fruit and cell expansion, grain maturation, and promoting the abscission of leaves, flowers and fruits. It also has effects such as inducing flower bud differentiation, breaking dormancy, promoting germination, inhibiting flowering, organ abscission, dwarfing plants and promoting adventitious root formation.

6. Brassinolide (BR)

Also known as brassin, rapeseed sterol lactone, it has a regulatory effect on all growth stages of crops, combining the comprehensive effects of gibberellins, cytokinins and auxins; and it has the function of balancing the development of the above-mentioned endogenous hormones in plants. The growth-promoting effect of brassinolide is very significant, and its effective concentration is several orders of magnitude lower than that of auxins.

7. Other types of plant growth regulating substances

Auxin-type regulators such as 2,4-D, naphthaleneacetic acid, indoleacetic acid and indolebutyric acid have varying degrees of effect in prompting cuttings to form adventitious roots.

After seeds are treated with PGRs such as gibberellins and cytokinins, the activity of hydrolases can be induced and enhanced, accelerating seed germination.

Auxins, gibberellins, cytokinins, brassinolide and others all have the effect of promoting cell elongation.

The above is an introduction to regulators. When farmers use regulators, the dosage should be appropriate; they must not arbitrarily increase the dosage, nor arbitrarily mix them, and the method of use must be proper. Growth regulators cannot replace the application of fertilizer.

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