Abstract
IN recent studies1–4 of the mechanism of action of plant growth-regulating compounds it has been postulated that active phenoxyacetic acids become attached at two points to a specific substrate within the cell, the points of attachment being the carboxyl group and a position in the ring ortho to the sidechain. So far, phenoxyacetic acids substituted in the 2- and 6-ring positions have not been regarded as active in the Avena straight-growth test. On the basis of other tests it has been put forward that high activity in chlorophenoxyacetic acids is associated with the presence of two unsubstituted positions in the ring para to each other. It has also been claimed that 2:6-dichlorophenoxyacetic acid and 2:4:6-trichlorophenoxyacetic acid are not themselves active but behave as anti-auxins. That is, when these compounds are mixed with either indolylacetic acid or 2:4-dichlorophenoxyacetic acid the resulting stimulation in extension growth of Avena coleoptiles is less than that induced by indolylacetic acid or 2:4-dichlorophenoxyacetic acid alone. Evidence of this type has led to the proposal that 2:6-substituted compounds have only a single point of attachment to the substrate and act as anti-auxins by blocking one of the two-point attachments of other more active compounds. From experiments carried out in this Department, however, it is now clear that the interpretation of the above results requires further consideration.
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OSBORNE, D., BLACKMAN, G., POWELL, R. et al. Growth-regulating Activity of Certain 2:6-Substituted Phenoxyacetic Acids. Nature 174, 742 (1954). https://doi.org/10.1038/174742a0
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DOI: https://doi.org/10.1038/174742a0
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