. Auxins and plant growth. Auxin; Plant growth promoting substances. 156 Fundamentals of Auxin Action activity has been obtained with 2,3,6-trichlorobenzoic acid (IX). In the benzoic acids, the 77ieta position appears to be the active site of reaction, and the substitutions in the other positions serve to activate the 7neta position (Thimann, 1952). It is interesting to note that as the acid side-chain shortens, the active site on the ring retreats to a position more remote from the side-chain. The importance of the ortho positions in other auxins such as indoleacetic and naphthaleneacetic is
. Auxins and plant growth. Auxin; Plant growth promoting substances. 156 Fundamentals of Auxin Action activity has been obtained with 2,3,6-trichlorobenzoic acid (IX). In the benzoic acids, the 77ieta position appears to be the active site of reaction, and the substitutions in the other positions serve to activate the 7neta position (Thimann, 1952). It is interesting to note that as the acid side-chain shortens, the active site on the ring retreats to a position more remote from the side-chain. The importance of the ortho positions in other auxins such as indoleacetic and naphthaleneacetic is obscure, but nevertheless the im- portant point made by the Muir theory is that the ring of an auxin must have an active position at which a reaction with another mate- rial is assumed to take place. This contribution has provided a corner- stone for some of the most provocative theories of auxin action, de- scribed in chapter VIII. Structure of the Side-Chain Changes in the acid side-chain can have a profound influence on auxin activity. For example, side-chains with two carbons or two carbons plus an oxygen appear to be optimal for auxin activity. Longer side-chains such as the propionic (X) and butyric acid (XI) derivatives are generally less active (Koepfli et nl, 1937). CH,CH,COOH f n nCH,CH,CH,COOH. 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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