Modulation of the oscillatory system involved in polar transport of auxin by other phytohormones

Abstract

A wave‐like pattern of the basipetal efflux of natural auxin from the cambial region of a series of consecutive short sections of stems of Larix decidua Mill., Acer pseudoplatanus L. and Picea abies (L.) Karst. has been demonstrated as it was earlier reported for Pinus silvestris L. Apical application of ABA suppressed the IAA‐stimulated increase of the auxin‐wave amplitude, and zeatin or GA3 prevented this repression in stem segments of Pinus silvestris. All the exogenously applied substances were highly effective in physiological concentrations. Already 20‐min of exposure to IAA or ABA at the apical end produced modulations of the auxin‐wave along the whole 6.6 cm long stem segment. Application of 2, 3, 5‐triiodobenzoic acid (TIBA) caused suppression of the wave‐like pattern of auxin efflux similarly as ABA, supporting the association of the modulatory effects of ABA with the phenomena involved in polar transport of auxin. Abscisic acid applied to the basal end of the stem segment also reduced the auxin‐wave amplification caused by simultaneous supply of IAA to the apical end. This finding additionally confirms the hypothesis that: 1) the supracellular auxin‐wave generation is associated with the functioning of a system of oscillators coupled at the cellular level and 2) the auxin‐wave modulations can be propagated acropetally, that is against the main direction of the auxin molecular transport.