. Auxins and plant growth. Auxin; Plant growth promoting substances. 166 Fundamentals of Auxin Action auxin concentrations. A summary of the large number of anti-auxins reported in the following three years is given by McRae and Bonner (1953). Modes of Action. The evidence concerning the molecular require- ments for auxin activity has led to the general conclusion that auxins act by becoming attached to other materials at two points. Thus an auxin must have an unsaturated ring which can be attached to some receptor (at the ortho position in the case of phenoxyacetic acids), and there must be a
. Auxins and plant growth. Auxin; Plant growth promoting substances. 166 Fundamentals of Auxin Action auxin concentrations. A summary of the large number of anti-auxins reported in the following three years is given by McRae and Bonner (1953). Modes of Action. The evidence concerning the molecular require- ments for auxin activity has led to the general conclusion that auxins act by becoming attached to other materials at two points. Thus an auxin must have an unsaturated ring which can be attached to some receptor (at the ortho position in the case of phenoxyacetic acids), and there must be an acid group which can combine with some recep- tor. By assuming that the ring and the acid attach to the same re- ceptor, Foster et al (1952) can account for the spatial configuration requirement as well. A provocative theory of the means of anti-auxin actions has been proposed by McRae and Bonner (1953). In their theory, anti-auxins are compounds which have some of the three requirements for auxin activity but fall short of having all three. Three types of anti-auxins O or CD. I M6/L CONC. OF AUXIN Fig. 74. An interaction between an auxin (naphthaleneacetic acid) and an anti- auxin (trans-cinnamic acid) in the pea straight-growth test, showing the inhibition of growth at low auxin concentrations by the anti-auxin (15 ), and the reversal of this inhibition by the presence of larger amounts of the auxin (van Overbeek et al, 1951).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Leopold, A. Carl (Aldo Carl), 1919-. Berkeley, University of California Press
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