Interaction of gibberellic acid & allyl trimethylammonium bromide upon growth of Ulothrix.

The ability of a series of choline analogs to produce a form of dwarfism in wheat was recently described by Tolbert (7). One of the more potent compounds tested was allyl trimethylammonium bromide (AMAB). The most characteristic effect upon the growth of Thatcher wheat after treatment of the roots with AMAB was the development of stockier plants with short thick stems. This pronounced dwarfism is associated with shorter internodal distances. These symptoms appeared quite the opposite of those produced by the application of gibberellin. Therefore, in extending their original observations, Tolbert (8) and Wittwer and Tolbert (9), particularly studied the antagonistic effect of gibberellin on AMAB in both wheat and tomato plants. At sufficiently hiigh concentrations gibberellin was able to reverse completely the morphological effects of the treatment with AMAB. A speculative mechanism was proposed in which the rather high degree of molecular structural specificity observed for growth inhibition activity was compared with the well characterized structural requirements for inhibition of acetylcholinesterase in mammalian systems. To gain insight into the mechanism of interaction of AMAB and gibberellins we studied their effects upon the growth of the unicellular filamentous green alga, Ulothrix subtillisima. This organism exhibits a particularly large and sensitive response to both indole acetic acid (IAA) and gibberellic acid (GA). At optimal concentrations of IAA a 13-fold stimulation of growth is obtained, both on the basis of net increase of wet weight and increase of cell number as demonstrated by Conrad et al. (2). Some of the advantages and disadvantages in using the algae to study plant growth substances have been reviewed recently by Conrad and Saltman (3). By working with this comparatively simple and undifferentiated system we have been able to demonstrate that not