The chemical structure of plant hormones has been known, and synthetic similar substances are called growth regulators, such as indoleacetic acid; Some can't be synthesized artificially, such as gibberellin. At present, gibberellin reagents sold in the market are all made from the culture filtrate of Gibberella. These indoleacetic acids and gibberellins added to plants are different in source from those produced by plants themselves, so they are also called exogenous plant hormones as plant growth regulators.
Recently, newly confirmed plant hormones include polyamines, salicylic acid, jasmonic acid (esters) and so on.
Plant hormones produced in plants include gibberellin, kinetin and abscisic acid. At present, some phytohormone-like substances can be synthesized artificially, such as 2,4-D (2,4-dichlorophenol diethyl phenol).
Trace organic substances produced by plants themselves and transported to other parts can regulate the growth and development of plants, which are called phytohormones. Synthetic substances with phytohormone activity are called plant growth regulators. There are five known plant hormones: auxin, gibberellin, cytokinin, abscisic acid and ethylene. Brassinosterol is gradually considered as the sixth kind of plant hormone.
plant hormone
1. About history
When D.Darwin studied plant movement in 1880, he only found the coordination of various hormones, and found that the tender shoots of plants were affected by unilateral illumination, which could spread to the elongation area of stems and cause bending. 1928, F.W. Winter of the Netherlands separated a physiologically active substance called auxin from the tip of oat coleoptile, which made the coleoptile elongate. 1934, F. Kaergel and others in the Netherlands obtained growth hormone crystals from human urine and identified them as indoleacetic acid.
2. Existing parts
Auxin is ubiquitous in lower and higher plants. Auxin is mainly concentrated in young and growing parts, such as the coleoptile of cereals, and its production has "self-promotion", such as the stem tip, young leaves, pollen and ovary of dicotyledonous plants, as well as the growing fruits and seeds. There is little content in aging organs.
It is proved by coleoptile cutting that auxin in plants can only be transported from the upper end to the lower end, but not vice versa. This mode of transportation is called polar transportation, which can be carried out much faster than diffusion. However, the transport direction of auxin drugs applied from the outside depends on the application site and concentration. For example, the auxin absorbed by roots can rise to the tender part of the ground with transpiration flow.
In plants, indoleacetic acid is synthesized from tryptophan by enzymatic reaction. The precursor of indole acetic acid synthesis in Cruciferae plants is indole acetonitrile, and there are quite a lot of indole ethanol in zucchini, which can also be converted into indole acetic acid. Synthetic auxin can be decomposed by enzymes in plants or external light, so it is in constant synthesis and decomposition.
Step 3: Function
1. Low concentration auxin can promote organ elongation.
Thereby reducing transpiration and water loss. When it exceeds the optimum concentration, it will lead to the production of ethylene, which will reduce the promotion of growth and even turn into inhibition. Different organs have different responses to auxin. Roots are the most sensitive, buds are the second, and stems are the worst. The main reason why auxin can promote cell elongation is that it can acidify the cell wall environment, increase the activity of hydrolase, relax the cell wall structure, increase the plasticity and increase the cell volume.
2. Auxin can also promote the synthesis of RNA and protein, and promote cell division and differentiation. Auxin has duality, which can not only promote plant growth, but also inhibit plant growth. Low concentration auxin promotes plant growth, while high concentration auxin inhibits plant growth. 2,4-D has been used as a selective herbicide.
4. About auxin analogues
Indoleacetic acid can be synthesized artificially. Synthetic auxin-like substances, such as indole propionic acid, indole butyric acid, naphthylacetic acid, 2,4 4- D, 4- iodophenoxyacetic acid, etc. Used in production, it can be used to prevent shedding, promote parthenocarpy, sparse flowers and fruits, take root in cuttings and prevent potato germination. Callus takes root easily; On the contrary, it is easy to germinate.
gibberellin
1. About history
During the research of rice bakanae disease in Akira Kurosawa, Japan from 65438 to 0926, it was found that the overgrowth and yellowing of diseased seedlings were related to Gibberella. In 1935, a physiologically active substance named gibberellin (GA) was isolated from the secretion of Gibberella. Since 1950s, British and American scientists have studied gibberellins. At present, more than 60 gibberellins have been isolated from Gibberella and higher plants, named GA 1, GA2, etc. Later, more than ten kinds of cytokinins were found in plants, and gibberellin widely existed in fungi, algae, ferns, gymnosperms and angiosperms. The commercially produced gibberellins are GA3, GA4 and GA7. GA3, also known as gibberellic acid, is the earliest gibberellin isolated and identified, and its molecular formula is c19H2O6. Namely 6- furylaminopurine.
2. There is a website
Gibberellin in higher plants mainly exists in young roots, young leaves, young seeds and fruits.
It is synthesized from mevalonate via kaurene and other intermediates. It is proved that gibberellin contains a component that can induce cell division. Gibberellin is nonpolar when transported in plants, usually transported upward from xylem and downward or bidirectional from phloem.
Step 3: Function
Gibberellin's most remarkable function is to promote the elongation of plant stems. Dwarf varieties without gibberellin synthesis gene can obviously cause stem elongation after gibberellin treatment. Gibberellin can also promote the leaf elongation of Gramineae plants. Gibberellin is often used to improve the yield of stem and leaf vegetables in vegetable production. Some biennial plants, which need low temperature and long sunshine, can blossom in 1 year after dry seeds absorb water, and gibberellin treatment can replace low temperature. Gibberellin can also promote fruit development and parthenocarpy, break the dormancy of tubers and seeds and promote germination. After dry seeds absorb water, gibberellin produced in embryos can induce the synthesis of α -amylase in aleurone layer, increase the activity of other hydrolases, promote starch hydrolysis and accelerate seed germination. At present, gibberellin is widely used in beer industry to promote the production of α-amylase, so as to avoid a large amount of organic matter consumption caused by barley seed germination, thus saving costs.
cytokinin
1. About history
The discovery of this substance began with the discovery of kinetin. It is transported downward or in both directions through phloem. From 65438 to 0955, F. Schugge of the United States accidentally discovered that adding DNA extracted from deteriorated herring sperm to the culture medium could promote the healthy growth of tobacco callus. It turns out that it contains an ingredient that can induce cell division, called kinetin. The first natural cytokinin is zeatin isolated from immature corn seeds by D.S. latham in 1964. Later, more than ten kinds of cytokinins and GA2 appeared. Found in plants. It is a derivative of adenine.
2. There is a website
Cytokinins in higher plants exist in roots, leaves, seeds, fruits and other parts of plants. Cytokinins synthesized by root tips can be transported upward to stems and leaves, but cytokinins can also be formed in immature fruits and seeds. The main physiological function of cytokinin is to promote cell division and prevent leaf senescence. The aging and yellowing of green plant leaves are due to the decomposition of protein and chlorophyll. Cytokinins can maintain the synthesis of protein, thus keeping leaves green and prolonging life.
Step 3: Function
Cytokinins can also promote bud differentiation. When their content in tissue culture is greater than auxin, callus is easy to germinate; On the contrary, it is easy to take root and sprout. Can be used for preventing abscission, promoting parthenocarpy, thinning flowers and fruits, rooting cuttings and preventing potato germination.
Synthetic cytokinin benzyl adenine is often used to prevent lettuce, celery and Chinese cabbage from aging and deterioration during storage.
abscisic acid
1. About history
In the early 1960s, abscisic acid, whose molecular formula is c 15 H2O 4, was isolated from young cotton fruits and birch leaves by F.T. Adicott of the United States and P.F. Wareing of the United Kingdom respectively.
2. There is a website
Abscisic acid exists in leaves, dormant buds and mature seeds of plants. Generally, it is more abundant in aging organs or tissues than in young parts.
Step 3: Function
Inhibit cell division, and promote the senescence and shedding of leaves and fruits. Inhibit seed germination. It inhibits the synthesis of RNA and protein, thus inhibiting the growth of stems and lateral buds, so it is a growth inhibitor, which is beneficial to the increase of cell volume. It has antagonistic effect with gibberellin. Abscisic acid can promote the abscission of petiole by promoting the formation of abscission layer, and can also promote the dormancy of buds and seeds. The higher abscisic acid content in seeds is the main reason for seed dormancy. After stratification, the seeds of peach, Korean pine, etc. Bud is the second, and it is easy to germinate because of the decrease of abscisic acid content. Abscisic acid is also related to the opening and closing of stomata. When wheat leaves are dry, the content of abscisic acid in guard cells increases and stomata close, thus reducing transpiration and water loss. The gravity movement of root tip is related to the distribution of abscisic acid. Synthetic parts: root cap, wilting leaves, etc.
ethylene
1. About history
As early as the beginning of the 20th century, people found that there was a gas that could promote the green lemon to turn yellow and mature when it was illuminated by gas lamps. This gas was ethylene. However, it was not until the early 1960 s that ethylene was listed as a plant hormone until a very small amount of ethylene was detected in immature fruits by gas chromatography.
2. There is a website
Ethylene widely exists in various tissues and organs of plants, and is converted from methionine under the condition of sufficient oxygen supply. Synthetic part: all parts of a plant.
Step 3: Function
Promote fruit ripening, promote organ shedding and aging. Its production has a "self-promoting effect", that is, the accumulation of ethylene can stimulate more ethylene production. Ethylene can promote the synthesis of RNA and protein, increase the permeability of cell membrane and accelerate respiration. Therefore, when the ethylene content in fruit increases, it can promote the transformation of organic matter and accelerate maturity. Ethylene can also promote organ loss and aging. Treating etiolated seedling stems with ethylene can make the stems thicker and the petioles grow upward. Ethylene can also increase the number of female flowers in melon plants, and in plants, it can promote the milk secretion of rubber trees and sumac trees.
4. Related applications
Ethylene is a gas, so it is inconvenient to apply it in the field. 2- chloroethylphosphonic acid (trade name ethephon), a liquid compound that can release ethylene, has been widely used in fruit ripening, defoliation before cotton harvest, promoting boll cracking and boll opening, stimulating rubber latex secretion, dwarfing rice, increasing female flowers of melon and promoting pineapple flowering.
Other hormones
There are mainly brassinolide, salicylic acid and jasmonic acid. At present, brassinosteroids are recognized as the sixth kind of plant hormones. Brassinosterol is a steroid hormone, and its mechanism of action is different from that of animal steroid hormones. It has physiological functions such as promoting cell elongation and cell division, promoting vascular differentiation, promoting pollen tube elongation to maintain male fertility, accelerating tissue aging, promoting lateral root development, maintaining apical dominance, and promoting seed germination. At present, the signal transduction pathway of brassinosteroids is also one of the frontiers and hotspots in current research.