Electrical and proton gradients in the sensory transduction of photophobic responses in the blue-green alga, Phormidium uncinatum

Abstract

The gliding filaments of the blue-green alga Phormidium uncinatum stop their movement almost instantaneously when transfered from their growth pH of 7.2 into a buffer ≤4.5 or ≥12.5. A pH jump into the range between 5.6 and 12.0 induces no visible response while in the range between 4.9 and 5.5 the organisms reverse the direction of their movement. The pH jump is believed to simulate an early step during the sensory transduction chain of the photophobic response which eventually results in a reversal of movement.

One of the subsequent steps is the inversion of an electric potential gradient existing between the front and rear ends of a filament which dictates the direction of movement. A similar reversal of the naturally existing potential gradient can be provoked by switching on an external do field when the filaments move towards the anode or switching it off when the filaments glide in the opposite direction. Implications of these results on the current model of sensory transduction of the photophobic response in Phormidium uncinatum are being discussed.