EFFECT OF INHIBITORS AND UNCOUPLERS ON LIGHT-INDUCED POTENTIAL CHANGES TRIGGERING PHOTOPHOBIC RESPONSES

The effects of inhibitors and uncouplers on light-induced potential changes have been studied to determine the mechanisms involved in sensory transduction in photophobic responses of the filamentous blue-green alga, Phormidium uncinatum. 1. DCMU and DBMIB, inhibitors of the photosynthetic electron transport chain, impair light-induced potential changes at about the same concentrations at which they inhibit photophobic responses. They seem to act by decreasing the photosynthetic electron flow rate and they do not decrease the resting potental of the cell. 2. The lipophilic cation TPMP+ which acts as an uncoupler with protonophorous properties blocks both photophobic responses and light-induced potential changes. TPMP+ inhibits the resting potential apparently through penetration of membranes causing a breakdown of the generated potentials. 3. Application of a small electric de field enhances the effect of an inhibitor, which indicates that both measures impair light-induced potential changes. These results support the hypothesis that sensory transduction in photophobic responses of blue-green algae is mediated by light-induced potential changes, the generations of which can be explained by the Mitchell chemiosmotic hypothesis. © 1979 Springer-Verlag.