The content of gibberellin-like (GA-like) substances in various parts of young alder (Alnus glutinosa (L.) Gaertn.) plants was estimated by means of the lettuce hypocotyl bioassay. The highest levels of GA-like activity were found in the root nodules, of dormant plants, plants emerging from dormancy, and plants in full leaf.
No major differences were found in the roots and leaves of nodulated as opposed to non-nodulated plants, although the stems of nodulated plants did contain lower levels of GA-like activity.
The detection of seasonal changes in GA-like activity in root nodules from mature trees was dependent upon the method of chromatography employed. One major peak of biological activity was detected following paper chromatography and no large changes were detected in the level of this component. In contrast, three zones of GA-like activity could be detected after thin layer chromatography (TLC) and there were marked seasonal changes in activity in these three zones. This can be attributed either to changes in levels of the GA-like substances themselves and/or to variations in the amounts of impurities interfering with the response of the bioassay.
A number of peaks of GA-like activity were detected by lettuce and rice bioassays following analysis of a large-scale extract on a preparative high performance liquid chromatograph (HPLC). However, both the total number and the identity of the substances responsible for this activity, remain to be determined.