Roots, shoots, and leaves of 1- and 2-year-old ungrafted plants of EM IX, VII, and I, and roots of EM XVIa, were extracted to detect an inhibitor that appears identical with abscisic acid (ABA). The extracts were coned, partially purified chromatographically, and bioassayed using the wheat coleoptile straight growth and Lepidium seed germination tests. A strongly inhibitory substance was found in both bioassays at or close to the Rf values reported for maximum ABA activity or determined with the synthetic form.
Extracts of EM IX tissue contained the highest levels of this inhibitor, presumed to be ABA. Progressively lower levels were found in extracts of EM VII, I, and XVIa, which is the same as the order of these clones in increasing vigor of grafted scions. This same order was indicated in nearly all bioassays of the 3 types of tissue extracts. Extracts of roots collected in early spring after overwintering either in storage or out-of-doors, in midsummer, and in the fall after cessation of growth all placed the clones in the same order. Levels in root and leaf extracts were generally higher than in those of shoots.
The Lepidium seed bioassay appears to offer a convenient method for identification of strongly or semi-dwarfing individuals or clones. Leaves offer an obvious advantage over shoots or roots.
Abscisic acid (ABA) at 1 and 10 μg/ml concn supplied to growing plants of ‘EM XVIa’ (very vigorous) through grafted living conduits of the same tissue and of ‘EM IX’ (very dwarfing) was inhibitory to growth during the first 10-14 days of treatment. The ‘EM IX’ tissues also had an inhibitory effect of their own, which ABA enhanced. The higher concn was more inhibitory but not proportionately so. During the first 10 days, 1 μg/ml ABA markedly reduced solution absorption below that of water. Absorption of all solutions by ‘EM IX’ tissues was in all cases less than by those of ‘EM XVIa’. A drastic decrease in absorption was evident after 10 days.
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