Types and functions of plant growth hormone

There are 6 types of plant growth hormones, namely auxin, Gibberellic Acid GA3, Cytokinin, ethylene, abscisic acid and brassinosteroids, BRs.

Plant growth hormone, also called plant natural hormones or plant endogenous hormones, refers to some trace amounts of organic compounds produced in plants that can regulate (promote, inhibit) their own physiological processes.

1. Types of plant growth hormone
There are currently five recognized categories of phytohormones, namely auxin, Gibberellic Acid GA3, Cytokinin, ethylene, and abscisic acid. Recently, brassinosteroids (BRs) have gradually been recognized as the sixth major category of phytohormones.
1. auxin
(1) Discovery: auxin is the earliest plant hormone discovered.
(2) Distribution: auxin is widely distributed in plants, but it is mainly distributed in vigorously growing and young parts. Such as: stem tip, root tip, fertilization chamber, etc.
(3) Transport: There are polar transport (can only be transported from the upper end of the morphology to the lower end and cannot be transported in the reverse direction) and non-polar transport phenomena. In the stem it is through the phloem, in the coleoptile it is the parenchyma cells, and in the leaf it is in the veins.

2.Gibberellic Acid (GA3)
(1) Named Gibberellic Acid GA3 in 1938; its chemical structure was identified in 1959.
(2) Synthesis site: Gibberellic Acid GA3 is commonly found in higher plants, and the site with the highest activity of Gibberellic Acid GA3 is the site of plant growth.
(3) Transportation: Gibberellic Acid GA3 does not have polar transport in plants. After synthesis in the body, it can be transported in two directions, downward through the phloem, and upward through the xylem and rising with the transpiration flow.

3. Cytokinin
(1) Discovery: From 1962 to 1964, natural Cytokinin was first isolated from sweet corn kernels at the early filling stage 11 to 16 days after fertilization, named zeatin and its chemical structure was identified.
(2) Transport and metabolism: Cytokinin is commonly found in vigorously growing, dividing tissues or organs, immature seeds, germinating seeds and growing fruits.

4. Abscisic acid
(1) Discovery: During the life cycle of a plant, if the living conditions are not suitable, some organs (such as fruits, leaves, etc.) will fall off; or at the end of the growing season, the leaves will fall off, stop growing, and enter dormancy. During these processes, plants produce a type of plant hormone that inhibits growth and development, namely abscisic acid. So abscisic acid is a signal of seed maturity and stress resistance.
(2) Synthesis site: Biosynthesis and metabolism of abscisic acid. Roots, stems, leaves, fruits, and seeds in plants can all synthesize abscisic acid.
(3) Transportation: abscisic acid can be transported in both xylem and phloem. Most are transported in the phloem.

5.Ethylene
(1) Ethylene is a gas that is lighter than air at the temperature and pressure of the physiological environment. Acts at the site of synthesis and is not transported.
(2) All organs of higher plants can produce ethylene, but the amount of ethylene released is different in different tissues, organs and development stages. For example, mature tissues release less ethylene, while meristems, seed germination, flowers that have just withered and fruits produce the most ethylene.

2. Physiological effects of plant growth hormone
1. Auxin:
Promotes plant growth. Promote cell division.
2. Gibberellic Acid GA3:
Promotes cell division and stem elongation. Promote bolting and flowering. Break dormancy. Promote male flower differentiation and increase seed setting rate.
3. Cytokinin:
Promotes cell division. Promote bud differentiation. Promote cell expansion. Promote the development of lateral buds and relieve the apical advantage.

3. Is plant growth regulator hormone?
1. Plant growth regulator is a hormone. Plant growth hormone refers to trace chemicals naturally present in plants that regulate and control plant growth and development. It is also called Plant endogenous hormones.
2. Plant growth regulato is obtained by artificial synthesis or extraction, as well as by microbial fermentation, etc., and is usually also called Plant exogenous hormones.
Namely, auxin, Gibberellic Acid (GA), Cytokinin (CTK), abscisic acid (ABA), ethyne (ETH) and brassinosteroid (BR). They are all simple small-molecule organic compounds, but their physiological effects are very complex and diverse. For example, they range from affecting cell division, elongation, and differentiation to affecting plant germination, rooting, flowering, fruiting, sex determination, dormancy, and abscission. Therefore, plant hormones play an important role in regulating and controlling plant growth and development.