PHOTOTROPISM OF THE PHYCOMYCES SPORANGIOPHORE - A COMPARISON WITH HIGHER-PLANTS

Abstract— The basic phenomena of Phycomyces phototropism are described and compared with those of Avena and Zea coleoptiles and the seedlings of Arabidopsis, Cucumis, Helianthus, Raphanus and Sesamum. Symmetric redistribution of growth rate during curvature, a feature characteristic of Phycomyces phototropism, can in some cases also be found in plants. Common features are: complex fiuence‐response curves, log‐linear fluence dependence of the phototropic latency, relatively slow bi‐exponential dark‐adaptation and fast light‐adaptation kinetics, action spectra indicating the ubiquitous flavin‐like photoreceptor(s) as well as other non‐flavin receptors, and spacial memory as indicated by phototropic reversal experiments. The problem how phototropic curvature is maintained continuously while the light‐growth response adapts, remains unexplained (“phototropism paradox”). For Phycomyces it is shown that some of the most basic information processes, which include contrast recognition, wavelength sensitivity and sensitivity recovery (sensor adaptation) are mediated by the photoreceptor systems. Copyright © 1990, Wiley Blackwell. All rights reserved