Auxin

Native auxins

indole-3-acetic acid (IAA) is the most abundant and the basic auxin. There are three more native — endogenous auxins. All auxins are compounds with aromatic ring and a carboxylic acid group:

4-Chloroindole-3-acetic acid (4-CI-IAA)

2-phenylacetic acid (PAA)

Indole-3-butyric acid (IBA)

Auxins are a class of plant hormones (or plant growth substances) with some morphogen-like characteristics. Auxins have a main role in coordination of many growth and behavioral processes in the plant's life cycle. they are essential for plant body development.

Auxins and their role in plant growth were first described by the Dutch scientist Frits Warmolt Went. Kenneth V. Thimann isolated auxin and found its chemical structure to be indole-3-acetic acid (IAA). Went and Thimann co-authored a book on plant hormones, Phytohormones, in 1937.

There are synthetic auxins, and in big doses they can be used as herbicides. Agent Orange is a mixture of synthetic auxins.

Auxin Media

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  The auxin signal cascade: In the absence of auxin, Aux/IAA bind to and suppress the transcriptional activity of ARFs. When auxin is present it forms a 'molecular glue' between TIR1 and Aux/IAAs, which leads to the degradation of these repressors. ARFs are then free to bind to DNA and to cause changes in transcription.

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  Auxin diffuses along the shaded side of the plant, and causes cellulose in the cell wall to break, allowing turgor (water pressure) to expand the cell.

References

A healthy Arabidopsis thaliana plant (left) next to an auxin signal-transduction mutant

Crown galls are caused by Agrobacterium tumefaciens bacteria; they produce and excrete auxin and cytokinin, which interfere with normal cell division and cause tumors.