MICHAEL K. BACH^ 



and 

 J . F E L L I G2 



Union Carbide Chemicals Company 



The Uptake and Fate of C "- labeled 

 2A-Oichlorophenoxyacet'ic Acid In Bean 



Stem Sections 



Ever since the first reports of the involvement of indole-3-acetic acid 

 (lAA) in the control of plant growth, considerable effort has been 

 expended in attempts to explain its mode of action. The relative 

 structural simplicity of the plant growth regulators, as compared to 

 the animal hormones, seemed to lend encouragement to the view that 

 the control mechanisms in plants might be comparatively simple. 

 The morphological manifestations of the action of growth regulators 

 are numerous indeed, but can be divided into three main categories: 

 Effects due to cell elongation, effects due to nondifferentiative cell 

 division, and effects due to cell division accompanied by differentia- 

 tion. Systems which show a cell elongation response to auxin appli- 

 cation have been studied extensively, and the results suggest an effect 

 on the cell wall and/or a stimulation of water uptake as the primary 

 mode of action (7). However, from a fundamental point of view, cell 

 elongation is only the second step of growth, since it must be preceded 

 by cell division. Furthermore, since cell elongation can be largely 

 explained by water uptake, while cell division requires the de novo 

 synthesis of new cell material (i.e., proteins and nucleic acids), the 

 latter process has much more appeal to the biochemist. Under physio- 

 logical conditions the auxins not only influence cell division, but also 

 the differentiation and the formation of new organs (e.g., rooting, 

 flowering, fruit set, etc.). These changes are very difficult to study 

 without a clear understanding of the control of simple mitosis. In 

 several tissues, however, plant growth regulators are known to pro- 

 mote cell division and callus formation without differentiation when 



^Subsequently: The Upjohn Company, Kalamazoo, Michigan. 



= Subsequently: Linde Company, Union Carbide, Tonawanda, New York. 



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