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Auxins (indole auxins)

The best-known phytohormones from the auxin family contain the indole ring system substituted, at its 3-position, with a short aliphatic side chain ending in a free carboxyl group. Their most common endogenous representative is indole-3-acetic acid (IAA). A variety of its ring- and side-chain substituted derivatives have been prepared by chemical means. Indole auxins are universally required for organized growth at the cellular, tissue, and whole-plant levels; they are widely used in plant tissue culture and for the rooting of cuttings. Native auxins are now mostly analyzed by methods based on mass spectroscopy. Plants synthesize indole auxins by pathways which may, or may not, include the amino acid, tryptophan. When the hormones become temporarily or permanently dispensable, they are conjugated with amino acids, sugars or myo-inositol, and metabolized by oxidation and/or decarboxylation. Auxin perception and signal transduction appear to include soluble auxin-binding proteins and auxin-responsive gene expression, but there are many missing links. A wealth of information on the topology of the, so far putative, auxin receptor(s) may, however, be deduced from the molecular structures of a large series of synthetic compounds with auxin activity, which have been studied by X-ray crystallography and computational methods.

phytohormone, auxin, indole-3-acetic acid, IAA, chemical synthesis, chemical stability, qualitative and quantitative analysis, bioassay, biogenesis, conjugation, metabolism, growth, polar transport, root induction, signal transduction, molecular structure

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