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

bromide (AMAB). Themostcharacteristic effect uponthe growth ofThatcher wheatafter treatment oftheroots withAMAB wasthedevelopment ofstockier plants withshortthick stems.Thispronounced dwarfism isassociated withshorter internodal distances. These symptoms appeared quite theopposite ofthosepro- ducedbytheapplication ofgibberellin. Therefore, inextending their original observations, Tolbert (8) andWittwerandTolbert (9),particularly studied theantagonistic effect ofgibberellin onAMAB in bothwheatandtomatoplants. Atsufficiently hiigh concentrations gibberellin wasabletoreverse com- pletely themorphological effects ofthetreatment withAMAB. A speculative mechanism wasproposed inwhichtherather highdegree ofmolecular struc- turalspecificity observed forgrowthinhibition ac- tivity was compared withthewellcharacterized structural requirements forinhibition ofacetylcho- linesterase inmammalian systems. Togaininsight intothemechanism ofinteraction ofAMAB andgibberellins we studied their effects uponthegrowthoftheunicellular filamentous green alga, Ulothrix subtillisima. Thisorganism exhibits a particularly largeandsensitive response toboth indole acetic acid(IAA)andgibberellic acid(GA). Atoptimal concentrations ofIAA a13-fold stimula- tion ofgrowth isobtained, bothonthebasis ofnetin- crease ofwetweight andincrease ofcell numberas demonstrated by Conradetal.(2).Someofthe advantages anddisadvantages inusingthealgaeto studyplant growthsubstances havebeenreviewed recently byConradandSaltman(3).By working withthiscomparatively simple andundifferentiated systemwe havebeenabletodemonstrate thatnot