[The influence of growth substances on the development of bioelectric potentials in plant tissues].

With hypocotyls of Helianthus annuus, coleoptiles of Zea mays and radicles of Vicia faba seedlings the relations between auxin distribution and the development of electric potential differences were examined. A. Experiments with Helianthus seedlings. 1. Removal of one of the cotyledons produces a transversal potential difference in the hypocotyl between the intact flank and that without cotyledon. With 10(-3)m KCl as contact solution the positive pole always lies on the intact side. 2. Unilateral supply of synthetic auxins in aqueous solution calls forth a comparable potential difference. The electric effect of the growth substances examined corresponds to their growth promoting power: G.A.<2,4-D<NAA≪IAA. 3. The character of the electric effect observed was analysed by using contact solutions of different concentrations. In all cases the positivating power of the flank richer in auxin increases with the dilution of the contact electrolyte. On the other hand, its highest concentration tested (10(-1)m) reversed the sign of the effect, letting the auxin side appear electronegative. This relation makes it probable that the electric reactions observed are produced by a change of prexisting membrane piffusion potentials. 4. Pretreatment of the hypocotyl with TIBA which is known to impede auxin translocation, almost prevents the development of the potential differences described. B. Experiments with Coleoptiles of Zea mays. It was examined how the auxin depletion caused by decapitation and the subsequent regeneration of a "physiological tip" influences the electric reactivity of the coleoptile. Using the geoelectric after-effect as a test it could be shown that the ability of the stump to produce potential differences reaches its minimum 2 hours after decapitation; after this time the organ gradually regains its original reactivity. The time-course of this change corresponds closely to that of the extension growth after decapitation. C. Experiments with radicles of Vicia faba. With Vicia-radicles the electric effects of low, growth-promoting and of higher, growth-retarding IAA-concentrations were compared. It appeared that both concentration-ranges induce equally directed potential differences. With 10(-3)m KCl as contact solution it was always the side supplied with auxin which appeared electropositive. If contact was made with 10(-1)m KCl the sign of the effect was reversed in both cases. In all phenomena examined the primary reaction of the auxin in its influence upon membrane diffusion potentials in living tissues is probably an increase of the specific charge of the responsible boundary layers which raises their ion selectivity.