Further evidence for the electron pool hypothesis. The effect of KCN and DSPD on the photophobic reaction in the filamentous blue-green alga Phormidium uncinatum

Signal perception and amplification in photoresponses of cyanobacteria

In addition to a number of other external stimuli, the gliding cyanobacterium, Phormidium uncinatum, uses light as a clue to control movement in order to find and stay in a microhabitat with optimal conditions for growth and survival of the population. Of the three photoresponses developed in cyanobacteria, phototaxis, photokinesis and photophobic responses, the latter are the most prominent for this task. Step-down phobic responses are mediated by the photosynthetic pigments and are linked to the linear electron-transport chain. A change in the fluence rate is reflected by a change in the proton-motive force which is amplifi.

Influence of electric fields on photophobic reactions in blue-green algae

The effect of external electric fields on photo-accumulations of Phormidium uncinatum in light traps has been studied. 1. In direct current fields the phobic reaction of trichoms leaving the light field is not impaired if a voltage of 2.5 V is not exceeded. With voltages between 3 and 7 V the trichoms are motile, but phobic reactions are cancelled, provided the organisms are oriented more or less parallel to the electric field lines. Higher voltages cause the algae to die within minutes. 2. Only alternating current fields of very low frequencies (less than or equal 10(-3) Hz) have similar effects. Sine waves are more effective than triangular ones, but less than square waves. A hypothesis is proposed according to which sensory transduction of photophobic reactions in blue-green algae is mediated by changes in the endogenous membrane potential. This potential might be interfered with by the application of an external electric field, thus inhibiting photophobic reactions.