1. Auxin (IAA)
Auxin is a type of endogenous hormone containing an unsaturated aromatic ring and an acetic acid side chain. The English abbreviation is IAA. The international common name is indole acetic acid (IAA). 4-Chloro-IAA, 5-hydroxy-IAA, naphthaleneacetic acid (NAA), indolebutyric acid, etc. are auxin-like substances. Therefore, it is customary to use indoleacetic acid as a synonym for auxin.
The growth-promoting effect of auxin is mainly to promote cell growth, especially cell elongation. It can also promote fruit development and rooting of cutting branches. But tissue auxin, which tends to age, has no effect.
Features:
① Top advantage;
② Cell nuclear division and cell longitudinal elongation;
③ The leaves are enlarged;
④ Cuttings and roots;
⑤ Callus;
⑥ Inhibit roots;
⑦ Open stomata;
⑧ Extend dormancy.
2. Gibberellin
In 1938, Japanese Yabuda Sadajiro and Sumiki Yusuke isolated this active substance from the filtrate of Gibberella culture medium and identified its chemical structure. Named gibberellic acid. By 1983, more than 60 gibberellic acid-like substances had been isolated and identified. Generally divided into two categories: free state and bound state, collectively called gibberellins, named GA1 and GA2 respectively. Different gibberellins have different biological activities, and gibberellic acid (GA3) has the highest activity.
The most prominent role of gibberellins is to accelerate cell elongation (gibberellins can increase the auxin content in plants, and auxin directly regulates cell elongation). It also promotes cell division. It can promote cell expansion (but does not cause acidification of cell walls).
Features:
① Prevent organ shedding and break dormancy;
② Promote the conversion of maltose (inducing the formation of α-amylase);
③ Promote vegetative growth (it does not promote the growth of roots, but significantly promotes the growth of stems and leaves).
3. Cytokinin (CTK)
Cytokinins (CTKs) are a class of plant hormones that promote cell division, induce bud formation, and promote their growth. In 1955, while studying plant tissue culture, Skoog and others from the United States discovered a substance that promotes cell division, which was named kinetin.
Its chemical name is 6-furfurylaminopurine. Kinetin does not exist in plants. Later, more than a dozen substances with kinetin physiological activity were isolated from plants. Now all substances with the same physiological activity as kinetin, whether natural or synthetic, are collectively called cytokinins.
Their basic structure is a 6-aminopurine ring. Natural cytokinins in plants include zeatin, dihydrozeatin, isopentenyl adenine, zeatin nucleoside, isopentenyl adenosine, etc. In addition to kinetin, synthetic cytokinins also include 6-benzylaminopurine.
Physiological effects
① Promote cell division and regulate their differentiation.
② Delay the degradation of protein and chlorophyll, delay aging, and have the effect of preserving green.
Features:
① Cytoplasmic division and lateral cell elongation;
② Remove the top advantage;
③ Promote bud differentiation;
④ Inhibit stem elongation;
⑤ Open stomata;
⑥ Inhibit the decomposition of chlorophyll.
4. Abscisic acid (ABA)
Abscisic acid (abbreviated as ABA) is one of the natural growth regulators of plants. The cost of natural active abscisic acid (+)-ABA and traditional chemical synthesis of abscisic acid is extremely high. Due to its high price and difference in activity, abscisic acid has not been widely used in agricultural production. Therefore, it is currently only used in large-scale agricultural production in developed countries such as Japan and the United States. Scientists from all over the world are looking for ways to produce natural abscisic acid cheaply.
The physiological effects of abscisic acid are mainly to induce dormancy and promote shedding. The effect of abscisic acid is also opposite to that of cytokinin. Abscisic acid antagonizes both gibberellin and cytokinin in plants.
Features:
① Promote shedding;
② Inhibit growth;
③ Promote dormancy;
④ Cause stomata to close;
⑤ Increase stress resistance;
⑥ Influence differentiation;
⑦ Regulate the development of seed embryos.
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, 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 function is mainly to promote fruit and cell expansion. Grains mature and promote the shedding of leaves, flowers and fruits. It also induces flower bud differentiation, breaks dormancy, promotes germination, inhibits flowering, organ shedding, dwarfs plants and promotes the formation of adventitious roots.
Ethylene is a gas and is difficult to apply in the field. It was not until the development of ethephon that practical ethylene plant growth regulators were provided for agriculture. The main products are ethephon, vinylsilicone, glycoxime, mecloniopyrazole, defoliation phosphine, and cycloheximide (cycloheximide). They all release ethylene, so they are collectively called ethylene releasing agents. At present, the most commonly used one at home and abroad is ethephon, which is widely used to accelerate fruit ripening, defoliate cotton before harvest, promote cotton bolls to crack and spit, stimulate rubber latex secretion, dwarf rice, increase female flowers of melons, and promote pineapple flowering.
Features:
① Triple reaction;
② Promote fruit ripening;
③ Promote leaf senescence;
④ Induce the occurrence of adventitious roots and root hairs;
⑤ Break the dormancy of plant seeds and buds;
⑥ Inhibits the flowering of many plants (but can induce and promote the flowering of pineapples and plants of the same genus);
⑦ In dioecious plants, the direction of sexual differentiation of flowers can be changed early in flower development.
6. Brassinolide (BR)
Also known as brassinoids and brassinosteroids, referred to as BR. It was discovered in rapeseed pollen in 1970 by Mitchell, an agronomist at the USDA Research Center. It has a regulatory effect on various growth stages of crops, and has the comprehensive effects of gibberellin, cytokinin and auxin; and it has the function of balancing the development of these endogenous hormones in plants. The growth-promoting effect of brassinosteroid is very significant, and its concentration is several orders of magnitude lower than that of auxin.
Its mechanism of action is to promote the pumping out of hydrogen ions by the proton pump of the cell membrane system, leading to acidification of the free space and relaxation of the cell wall to promote growth. Brassinosteroids can also inhibit the activity of auxin oxidase, regulate the content of endogenous auxin in plants, and regulate plant growth. Brassinosteroids can also regulate the distribution of nutrients in plants and promote the growth of weak branches. Brassinosteroids can also affect the metabolism of nucleic acid substances and delay the aging of plant cells in vitro.
At present, more than 40 types of brassinosteroid compounds have been found in various crops, and they are collectively called brassinosteroid compounds (BRs for short). They are widely distributed in plants of different families and genera and in different organs of plants, and their physiological activities and contents are also different. Among them, the one with higher content and strongest activity is called brassinosteroid in rapeseed pollen. At present, there are artificially synthesized brassinosteroids, also called epi-brassinolides or brassinolides (BR), and their application effects are the same as natural brassinolides.
Features:
① Break dormancy and promote seed germination;
② Promote the development of weak organ parts;
③ Improve pollen fertilization and increase fruit setting rate;
④ Break the top advantage and promote the germination of lateral buds;
⑤ Regulate the distribution of nutrients in plants;
⑥ Promote cell division, increase leaf size, and promote fruit enlargement;
⑦ Promote photosynthesis, increase chlorophyll content, and delay leaf aging;
⑧ Improve plant physiological metabolism and increase the synthesis of proteins, sugars and other nutrients;
⑨ Enhance stress resistance and reduce the harm of adverse environments (temperature, disease, pesticides, salt resistance, drought).
