DIORTHO SUBSTITUTED PHENOXYACETIC ACIDS AS ANTIAUXINS

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Abstract
It has been shown by use of the Lineweaver-Burk treatment for competitive inhibition that 2,6-DCPA and 2,4,6-TCPA act not only as growth inhibitors but as anti-auxins, competitively antagonizing both IAA-induced and 2,4-D-induced growth of Avena coleoptile sections. The KI for 2,4,6-TCPA is approx. half that for 2,6-DCPA and the former compound is therefore the more effective antiauxin. It is suggested that an active auxin may be converted to an anti-auxin by elimination of either of the 2 essential functional groups. These are, respectively, the carboxyl group and the reactive ortho position. Disturbance of the spatial relationships between these 2 essential functional groups may also result in antiauxin activity. Thus anti-auxin apDears to be a substance capable of making only a single point attachment to the auxin-receptive site within the plant: a substance which in this way prevents auxins from consummating the growth-essential 2-point attachment at the same site.

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