Effects of Ethephon, 1-Aminocyclopropane-1-carboxylic Acid, and Inhibitors of Ethylene Synthesis on the Gravitropically Induced Movement of Mimosa pudica Pulvinus

Abstract

Primary pulvini of M. pudica L. displaced from their position display gravitropic movements beginning .apprx. 15 min after their reorientation. Ethephon, an ethylene-releasing compound, and 1-aminocyclopropane-1-carboxylic acid, an intermediate in ethylene biosynthesis, enhance these movements at a concentration as low as 10 nM. Inhibitors of ethylene synthesis (L-.alpha.-(2-aminoethoxyvinyl)glycine, (aminooxy)acetic acid and Co2+) reduce the amplitude of the movements. The promotive action of 1-aminocyclopropane-1-carboxylic acid is abolished by L-.alpha.-(2-aminoethyoxyvinyl)glycine. Ethylene may modify the curvature movement but not the initiation of the gravitropic reaction. With reference to the pulvinus functioning based on turgor variations and ion migrations inside the organ, namely K+ acting as the osmoticum, ethylene may act by increasing the membrane permeability to water and/or by altering an ion pump.