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Introduction and functions of Plant auxin

Date: 2024-05-19 14:56:35
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Auxin is indole-3-acetic acid, with the molecular formula C10H9NO2. It is the earliest hormone discovered to promote plant growth. The English word comes from the Greek word auxein (to grow).
The pure product of indole-3-acetic acid is white crystal and is insoluble in water. Easily soluble in organic solvents such as ethanol and ether. It is easily oxidized and turns into rose red under light, and its physiological activity is also reduced. Indole-3-acetic acid in plants may be in a free state or in a bound (bound) state. The latter are mostly ester or peptide complexes.

The content of free indole-3-acetic acid in plants is very low, about 1-100 micrograms per kilogram of fresh weight. It varies depending on the location and tissue type. The content in vigorously growing tissues or organs such as growing points and pollen is relatively low.
Many Plant auxins also play a role in cell division and differentiation, fruit development, root formation when taking cuttings and defoliation. The most important naturally occurring auxin is β-indole-3-acetic acid. Artificially synthesized plant growth regulators with similar effects include brassinolide, cytokinin, gibberellin, Naphthalene acetic acid(NAA), DA-6, etc.

The role of Auxin is dual: it can both promote growth and inhibit growth;
it can both accelerate and inhibit germination; it can prevent flower and fruit drop and thin flowers and fruits. This is related to the sensitivity of Auxin concentration to different parts of the plant. Generally speaking, plant roots are more sensitive than buds than stems. Dicotyledons are more sensitive than monocots. Therefore, auxin analogs such as 2-4D can be used as herbicides. It is characterized by its double-sided nature, which can both promote growth, inhibit growth, and even kill plants. 

The stimulating effect of Auxin is specifically manifested in two aspects: promotion and inhibition:
 Auxin has a promoting effect:
1. Formation of female flowers
2. Parthenocarpy, growth of ovary wall
3. Differentiation of vascular bundles
4. Expansion of leaves, formation of lateral roots
5. Growth of seeds and fruits, wound healing
6. Apical dominance, etc.

Auxin has inhibitory effects:
1. Flower abscission,
2. Fruit abscission, young leaf abscission, side branch growth,
3. Root formation, etc.

The effect of auxin on plant growth depends on the concentration of auxin, the type of plant, and the plant. related to organs (roots, stems, buds, etc.). Generally speaking, low concentrations can promote growth, while high concentrations can inhibit growth or even cause plant death. Dicotyledonous plants are more sensitive to Auxin than monocotyledonous plants; vegetative organs are more sensitive than reproductive organs; roots are more sensitive than buds, and buds are more sensitive than stems, etc.
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