Auxin
Botany · Developmental Biology
Say it: AWK-sin
Auxin is a plant hormone, chiefly indole-3-acetic acid, that controls cell elongation, bending toward light and the overall shape of a plant.
Also: auxins, indole-3-acetic acid, IAA, indoleacetic acid
Definition
What is auxin?
Auxins are a group of plant hormones, and the main natural one is indole-3-acetic acid, or IAA. It is made mostly in the growing tips of shoots and in young leaves, and it moves through the plant in a set direction, from cell to cell, carried by transport proteins such as the PIN family. This polar transport lets the plant build up auxin in some tissues and deplete it in others, and those differences act as signals that guide growth and development.
Auxin makes cells elongate by loosening their walls. When light comes from one side, auxin collects on the shaded side of a shoot, those cells grow longer, and the shoot bends toward the light. This is phototropism, which Charles Darwin and his son studied in grass seedlings. Auxin also drives gravitropism, keeps side buds dormant so the main shoot grows strongest (apical dominance), helps form vascular tissue and new roots, and influences flowering, fruit development and leaf fall.
Gardeners dip cuttings in auxin rooting products to help them form roots, and synthetic auxins such as 2,4-D are widely used as weedkillers.
Word parts
Where does the word “auxin” come from?
- aux-
- to grow, increaseGreek auxein
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Terms that go with it
- HormoneA hormone is a chemical messenger released into the blood by a gland or cell that changes the activity of distant target cells with matching receptors.
- ReceptorA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- Cell differentiationCell differentiation is the process by which an unspecialized cell becomes a specialized type, such as a neuron or muscle cell, by switching on a set of genes.
- Gene expressionGene expression is the use of a gene's information to make a working product, usually a protein or a functional RNA molecule.
- MorphogenA morphogen is a signaling molecule that spreads through developing tissue as a gradient, so cells adopt different fates depending on how much they receive.
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Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 30.6 Plant Sensory Systems and Responses
- Weijers, Nemhauser and Yang (2018), Auxin: small molecule, big impact, Journal of Experimental Botany
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