Researches on plant growth regulators XVI. The effect of plant growth substances on coacervates

Abstract

1. 1. In order to test the hypothesis that the action of synthetic compounds active as plant growth substances is localized largely in the protoplasmic membrane (influencing permeability), the influence of this type of compounds upon coacervates was studied. In case of the hypothesis being valid, a turgescent action upon the coacervate would be expected, running parallel with the physiological activity. 2. 2.a. In the series of naphthalene (1) acetic acid, di-, tetra- and decahydronaphthalene (1) acetic acid there is an increase of turgescent upon oleate coacervates. In botanical objects, however, physiological activity decreases in the same sequence. b. The turgescent action upon an oleate coacervate in trans- 1, 2, 3, 4-tetrahhydronapthylidine (1) acetic acid is stronger than in its cis-isomer, whereas, in contrast with the cis-form, the trans-isomer exerts no growth promoting action. c. Replacement of the carboxyl-group of stronger acidic character causes a decrease of growth substance activity; with the oleate coacervate the reverse is observed. d. In the homologous series of naphthalene (1)-acetic acid, -propionic acid and -butyric acid the influence upon the oleate coacervate increases (due to the fact that — in this sequence — the added substance is increasingly adsorbed by the soap micelles). The physiological activity in these series shows a decline, accompanied by a certain oscillation. e. With the oleate coacervate the relative activities of acetic acid and trichloroacetic acid are in accordance with the expectations based on the hypothesis. 3. 3. In general the action of the anions of acids with growth substance activity and related compounds on the oleate coacervate can be explained by the rules given previously (Bungenberg De Jong). 4. 4. All the compounds with growth substance activity show the expected turgescent effect in coacervate systems (serving as a model for the protoplasmic membrane); in a quantitative measure, however, the course is not parallel to the physiological activity, but just the reverse. 5. 5. This difference will have to be explained either by the fact that the relations growth substance/coacervate and growth substance/protoplasmic membrane are not sufficiently comparable (in other words, that the oleate coacervate as a model lacks completeness) or by the circumstance that an essential part of the growth substance activity — in contrast with the hypothesis — is not localized in the membrane. On the strength of several arguments given the latter explanation must be considered to be the likeliest one. 6. 6. It seems probable that the growth substance action unfolds itself largely in the protoplasm and that therefore the growth substances will have to pass the membrane. In that case the influence of the ph on growth substance activity becomes plausible, as the non-dissociated molecules of the acids permeate much more easily than their anions. 7. 7. A more detailed analysis of growth substance action on the basis of results of comparative investigations on models and biological objects is presented in the next paper.