. 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). Metabolism and mode of action respiration diminishes however with increasing external osmotic concentra- tion and disappears at an external osmotic concentration of 0-4 M in which elongation is reduced to a low value. These results parallel those obtained with Jerusalem artichoke storage tissue (Bonner, Bandurski, and Millerd, 1953). It has been concluded that the Avena coleoptile is at all times essentially in
. 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). Metabolism and mode of action respiration diminishes however with increasing external osmotic concentra- tion and disappears at an external osmotic concentration of 0-4 M in which elongation is reduced to a low value. These results parallel those obtained with Jerusalem artichoke storage tissue (Bonner, Bandurski, and Millerd, 1953). It has been concluded that the Avena coleoptile is at all times essentially in diffusion pressure deficit equilibrium with the external medium. No movement of water against a gradient appears to take place in coleop- tile sections (Burstrom, 1953b). When non-absorbable solutes are used to constitute a hypertonic solution no elongation of the tissue takes place. Adjustments of osmotic concentration take place in the coleoptile provided that an absorbable solute is present in the external medium. These osmotic ^0- I so 20-. 10 Figure 10. Rate of respiration of Avena coleoptile sections in the presence or absence of lAA (5 mgjl.) as a function of external solute concentration. After Ordin et al. (1955). 0-1 0-2 0-3 Molarity of mannifol OH adjustments are, however, independent of auxin and occur in the absence as well as in the presence of added growth substances. Since auxin-induced water uptake by the section is a purely osmotic phenomenon it must take place in response to a gradient into the tissue, which is, however, so small as to be not measurable by the present methods. Classical osmotic lore tells us that the of a cell equals osmotic concentration less cell wall pressure. Auxin does not appear to directly influence internal osmotic concentration. It must be concluded therefore that auxin in some way decreases cell-wall pressure. We have arrived by a circuitous route at a conclusion reached by Heyn 24 years ago (Heyn, 1931). The hy
Size: 3169px × 788px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodiver, booksubjectgrowthplants
