A team of researchers from RIKEN (Institute for Research in Physics and Chemistry) and University of Tokyo has identified compounds that inhibit the action of a plant hormone called auxin, which allowed them of information on the synthesis of this substance essential for plant development. Discovered in 1926, the auxin (or indole-acetic acid) is among the first identified plant hormones. Present throughout the plant kingdom, it plays an essential role in the process of plant growth depending on its concentration and the body on which it acts, it is involved in cell elongation, the formation of roots or bud formation. If auxin is well known to researchers, the process of bio-synthesis of this hormone remains obscure.

To better understand this process, researchers have searched for chemicals capable of regulating the activity of auxin. The database AtGenExpress [1] has enabled them to identify a potent inhibitor of auxin, amino ethoxyvinylglycine (AVG). For screening, they then discovered other inhibitors such as L-amino acid-oxyphénylpropionique (L-AOPP). When the researchers treated with various plant some of these chemicals, this has resulted in a decrease of 50% of the amount of auxin in these plants. In particular, treatment of specimens in Arabidopsis thaliana L-AOPP inhibited root growth. This anomaly could then be corrected by an external supply of auxin.

Researchers have found that different inhibitors have structural similarities with L-tryptophan, a precursor of auxin. Inhibitors appear to block the action of an enzyme, tryptophan transaminase, thus emerging as an important player in the bio-synthesis of auxin.

The various compounds inhibiting the synthesis of auxin, which have different effects depending on the species and the organ to which they are applied are so many new tools to advance the study of the synthesis and function of ‘auxin, which opens up possibilities for new methods of agricultural production.

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[1] AtGenExpress is an international project started in 2004 whose purpose is to study the transcriptome of Arabidopsis thaliana, a model plant for genetic research. The project brings together Japanese researchers (working at RIKEN), but also researchers from Germany, Swiss, English and American. These have established a database of expression profiles of Arabidopsis thaliana specimens subjected to various types of stress: biotic, abiotic, chemical … The database is freely available online.

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