The identification of (+)-abscisin II [(+)-dormin] in plants and measurement of its concentrations.

(+)-Abscisin II[(+)-dormin] has been identified in the ether soluble acid fraction of twenty plant species, including mono-and dicotyledons and a fern. (+)-Abscisin II was identified by its general physical properties, biological activity, chromatographic behaviour and optical rotatory dispersion. Synthetic abscisin II runs on paper chromatograms at the same RF as inhibitor-β from potato tuber and lemon fruit in the solvent mixtures used by previous workers, furthermore the growth-inhibitory activity of these extracts was attributable to the (+)-abscisin II contents. The concentrations of (+)-abscisin II in extracts of a number of plants were calculated from the specific rotation at the first, positive extremum (289 mμ) of the optical rotatory dispersion curve after extraction and chromatographic procedures.A new method of measurement was evolved, analogous to inverse isotope dilution, where a known quantity of racemic abscisin II was added to a tissue homogenate and then the total abscisin II in a highly purified extract was measured spectrophotometrically and the natural (+)-abscisin II measured spectropolarimetrically. The (+)-abscisin II content in the original sample was then calculated from the ratio of these two measurements and the known weight of racemic material added. Concentrations of (+)-abscisin II within tissues obtained by this technique were about three times higher than by the standard extraction procedure.Identification of several previously described growth-inhibitory compounds as (+)-abscisin II has extended the known physiological effects of the compound; its roles as a dormancy and an abscission factor and as a germination inhibitor are discussed.