Ordin, Lawrence and Cleland, Robert and Bonner, James (1955) Influence of Auxin on Cell-Wall Metabolism. Proceedings of the National Academy of Sciences of the United States of America, 41 (12). pp. 1023-1029. ISSN 0027-8424 http://resolver.caltech.edu/CaltechAUTHORS:ORDpnas55
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The plant hormone auxin (indole-3-acetic acid, IAA) controls rate of increase in size of the cells of many plant tissues. Thus, excised sections of the oat coleoptile respond to addition of the hormone by increasing more rapidly in length. It is known that the auxin-induced increase in cell volume of the oat section is immediately due to the uptake of water by the cell . Auxin-induced uptake of water by the coleoptile is in turn an osmotic phenomenon . Net water uptake by the coleoptile section takes place when the diffusion-pressure deficit of the section, DPDf, is greater than the diffusion-pressure deficit of the external solution with which the section is in contact, DPDo. DPDi is in turn determined by the relation DPDi = Osmotic concentration of cell contents - Wall pressure. (1) It has been indicated  that in the oat coleoptile section, auxin may increase DPDi by decreasing the wall-pressure term of equation (1). This conclusion, arrived at by study of the osmotic relations of the coleoptile, was reached by Heyn in 1931 on the basis of measurements of tissue plasticity as influenced by auxin . The problem of how auxin increases tissue growth rate is then the problem of how auxin brings about relaxation of cell-wall pressure. In the present communication it will be shown that auxin influences a particular facet of the metabolism of the cell wall of the coleoptile. It has been found that the methyl carbon of C14-methyl-labeled methionine is incorporated into cell-wall material. The rate of methyl carbon incorporation into, a particular portion of the cell-wall material, the hot-water-soluble portion, is increased in.the presence of auxin. Much of the carbon incorporated is removable in a manner .characteristic of methyl ester groups. There is also an auxin-induced increase in the rate of incorporation of glucose-derived carbon into the hot-water-soluble fraction. It is suggested that the physical properties of the cell wall may be affected by the hormonally influenced methyl carbon incorporation into and synthesis of particular cell-wall components. The experimental finding is of interest, since it constitutes a metabolic effect of the auxin which is detectable within short time periods.
|Additional Information:||Copyright © 1955 by the National Academy of Sciences Communicated September 4, 1955 Report of work supported in part by the Herman Frasch Foundation and in part by the National Science Foundation. [[L.O. was a] Postdoctoral Fellow, National Science Foundation.|
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