The chemical nature of a plant growth inhibitor in potato tuber peel, the ‘Inhibitor-β’ which commonly occurs on chromatograms of many plant extracts, has been examined. The inhibition, as indicated by bioassays using wheat coleoptile sections, could not be associated with any particular compound, but was partly or entirely due to a complex mixture of aliphatic acids. . Azelaic acid and the coumarin, acopoletin, were isolated together with a new substance, Acid A; degradative evidence is not sufficient to enable a complete structure to be proposed for this acid, but it appears to be an unsaturated polyhydroxy fatty acid. The growth of coleoptile sections in solutions of β at several concentrations was examined over the first 7 hours of growth. Inhibition did not occur until 4 hours; visible damage to the cells of the tissues appeared after this period. When β was examined in a mixture with 3-indolylacetic acid, inhibition was evident after 1 hour. These results are interpreted and the chemical system in which β may operate in growth is briefly considered.
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Housley et al. (1958) studied this question.