Relationship between Structure and Flower-inducing Activity of Benzoic Acid Derivatives in Lemna paucicostata 151

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Abstract
Lemna paucicostata, strain 151, does not flower when grown in 1/10 strength M medium containing 1% sucrose, but easily flowers when benzoic acid or its substituted derivatives are added to the medium. The structure-activity relationship of benzoic acid derivatives are quantitatively analyzable by means of physicochemical parameters. Aromatic substituent constants a (electronic parameter) and Vw (van der Waals volume steric parameter) delineate the variations in the flower-inducing activity, i.e., the higher the electron-withdrawing ability as well as the less the bulkiness of the substituents, the higher the activity. The exceptions are the derivatives substituted with NO2 at any position and with OH at meta and para positions; they exhibit an activity lower than expected from their substituent parameters. 2-Hydroxybenzoic acid (salicylic acid) exhibits activity higher than the calculated value, suggesting participation of the chelating effect in the flower-inducing activity besides electronic and steric effects. The molecular form responsible for the activity is suggested to be an undissociated neutral species.