Surface Activity as Related to Physiological Activity of Plant Growth-Regulators

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Abstract
The suppressive effect of plant growth-regulators upon the polarographic O2 max. has been used as a measure of the activity of these substances at a phase boundary. This suppressive effect was detd. for 25 compounds, including substances which promote the straight growth of Avena coleoptile sections and substances which are inactive in this respect. There is no correlation of surface activity measured in this way with physiological activity. In contradiction of the hypothesis that a pronounced effect in suppression of the O2 max. is a characteristic of plant growth-regulators, 2, 6-dichlorobenzoic acid exerts little if any suppressive effect upon the O2 max., yet has considerable physiological activity. It is concluded that chemical reactivity is more important than absorbability for the manifestation of growth-regulating properties by organic compounds.