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.

In continuation of experiments with photo-system II inhibitors [3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropylbenzo-quinone] the effect of photosystem I inhibitors was studied. 1. Neither the plastocyanin inhibitor, potassium cyanide, nor the ferredoxin antagonist, disalicyliden propandiamin, markedly affected those phobic reactions which are mediated by the electron transport via photosystem II into the electron pool. 2. On the other hand those phobic reactions, which are triggered by an increased flow of electrons out of the pool, are specifically inhibited by both substances. These results are regarded as further evidence that there is only one electron pool, the level of which triggers photophobic reactions and is located in the linear electron transport chain near photosystem II.