Studies on plant growth‐regulating substances

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Abstract
SUMMARY: The metabolism of certain 2,6‐disubstituted phenols that possess high auxin activity in the pea segment, pea curvature and tomato‐leaf epinasty tests, but are much less active in the wheat cylinder test, has been investigated in wheat, pea and tomato tissue. Metabolites were identified by thin‐layer chromatography and a semi‐quantitative assay method was developed.The low activity of 2,6‐dihalogenophenols and inactivity of 2‐halogeno‐6‐nitro‐phenols and 3‐halogeno‐2‐hydroxybenzonitriles in the wheat cylinder test was caused by rapid metabolic conversion of the compounds in this tissue to inactive compounds by a process involving hydroxylation of the aromatic ring in the para‐ position. No such inactivation occurred in pea and tomato tissues.Evidence for a novel detoxification of nitrophenols within both pea and wheat tissue was obtained; 2‐bromo–6‐nitrophenol was converted via 2‐bromo‐6‐aminophenol to N‐acetyl‐2‐bromo‐6‐aminophenol.Certain 3‐halogeno‐2‐hydroxybenzaldehydes and corresponding aceto‐phenones, although fulfilling the necessary structural and electronic criteria for auxin activity, are inactive. Metabolic studies indicate that this is because they are metabolized in wheat, pea and tomato tissues to compounds not possessing the structural requirements for auxin activity.