Structural Requirements of Phenoxyalkanoic Acids and Related Compounds for Promotion of Flowering in Sagittaria pygmaea Miq.

Abstract

The flowering of a perennial paddy weed, Sagittaria pygmaea (S. pygmaea) Miq., was promoted by 2,6-diisopropylphenoxyacetic acid, as well as by gibberellin A3 (GA3). Therefore, structural requirements of phenoxyalkanoic acids and related compounds for promotion of flowering in the weed were investigated. Among the synthesized phenoxyalkanoic acids, only the compounds having two bulky alkyl substituents on the 2- and 6-positions of the phenyl ring promoted flowering. In particular, 2,6-diisopropyl- and 2,6-di-tert-butylphenoxyacetic acids were highly effective promoters of flowering. 2,6-Diisopropylphenylacetic and -thioacetic acids were also active, but the corresponding phenylaminoacetic acid and a benzoic acid analogue were inactive on the promotion of flowering of the weed. Although the active compounds including 2,6-diisopropylphenoxyacetic acid may be classified as anti-auxins, typical anti-auxins including 2,6-dichlorophenoxyacetic acid did not promote flowering. These results demonstrate that the structural requirements of these compounds for promotion of flowering of S. pygmaea are somewhat similar but not identical to those for anti-auxins. Keywords: Flowering; phenoxyalkanoic acid; Sagittaria pygmaea Miq.; structural requirements