LIGHT REACTION SYSTEMS IN CYANOPHYCEAE*

Abstract— In the blue green algae, Phormidium uncinatum and Ph. autumnale, movement in the dark is arrested by 2 × 10‐‐4 M DCPIP†, whereas photokinesis, i.e. the acceleration of the movement by light, is not markedly impaired. Thus at this concentration movement occurs in the light, but not in the dark. Obviously, the dark movement is coupled with oxidative phosphoiylation and the inhibitory effect of DCPLP is probably due to trapping of electrons from the cytochrome chain and uncoupling of the oxidative phosphorylation whereas photophosphorylation in vivo is not uncoupled and accordingly photokinesis is not inhibited. On the other hand, the dark movement is not influenced by 10‐‐4 M DCMU, a high concentration, which otherwise stops both cyclic and non‐cyclic photophosphorylation and hence photokinesis. The inhibition by DCMU of that part of the light induced movement which is due to non‐cyclic phosphorylation is reversible by the addition of ferrocyanide (10‐‐2 to 10‐‐4 M) as external electron donor. The photo‐phobotactic response is less sensitive to DCMU and is not completely suppressed even at 10‐‐3 M. The inhibition is not significantly reversible by the addition of ferrocyanide. However, 10‐‐4 M DCPIP, that does not considerably impair photokinesis, suppresses the photo‐phobotactic responx completely. Thus, contrary to Links' hypothesis, photo‐phobotaxis cannot be linked with photophosphorylation. But there is some evidence that photo‐phobotaxis is coupled with the non‐cyclic electron transport of photosynthesis at another point, which seems to lie between electron supply from oxygen and the inhibition point of DCMU, probably in the region of the acmssory pigments.