. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). The mode of growth action of some naphthoxy compounds This prompted an investigation of the interaction between 3-indoleacetic acid and 3-indolewobutyric acid, the resuk of which is presented in Figure 3. In the best agreement with the last-mentioned resuks it shows that the actions of the two acids are strictly additive. The f^obutyric acid causes a constant promotion of elongation even when the auxin addition
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). The mode of growth action of some naphthoxy compounds This prompted an investigation of the interaction between 3-indoleacetic acid and 3-indolewobutyric acid, the resuk of which is presented in Figure 3. In the best agreement with the last-mentioned resuks it shows that the actions of the two acids are strictly additive. The f^obutyric acid causes a constant promotion of elongation even when the auxin addition has reduced elongation to practically nil. If any conclusions at all can be drawn on the mode of interaction of the compounds from the shape of activity curves, the logical conclusion in the present instance must be that the root-growth-inhibiting auxins and the root-growth promoters of the zjobutyric acid type act in two physiologically different systems, and that they do not simply compete in one single reaction Figure 3. The interaction between 3-indoleacetic acid (lAA) and 3-indole- isobutyric acid (liBA) on cell elon- mediating the cell elongation. Thus 3-indole/5obutyric acid should not be an anti-auxin according to the definition, but a root-growth promoter, a root auxin, with an action of some other kind. THE LOCATION OF THE ACIDS IN THE CELL-ELONGATION MECHANISM In order to find an explanation of this unexpected result we must turn to the mechanism of cell elongation itself, and see if it affords some ground for an assumption of independent modes of action of these compounds. This mechanism has been studied extensively on roots (cf Burstrom, 1942; 1954), and the results have led to a hypothesis summarized in Figure 4. It implies that the elongation takes place in two steps, the first phase involving a passive, plastic stretching of the cell wall, the second phase an active growth of the wall. The first one may be regarded as a preparatory reaction, neces
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