On the relation between phototaxis and photosynthesis in Rhodospirillum Rubrum

Abstract

The relation between phototaxis and photosynthesis in Rhodospirillum rubrum has been studied. The light intensity at which saturation is reached in photosynthesis proved to coincide with that at which the contrast sensitivity starts to decrease.

Potassium cyanide, which preferably inhibits the Blackman reaction in photosynthesis, decreases the light intensity at which the contrast sensitivity starts to decrease.

Ethyl urethan, which preferably affects the energy transfer in photosynthesis, increases this intensity.

These data strongly support Manten's hypothesis, according to which phototaxis is based on a sudden decrease of the photosynthetic rate.