The role of phospholipids in regulating photosynthetic electron transport activities: Treatment of thylakoids with phospholipase C.

The involvement of phospholipids in the regulation of photosynthetic electron transport activities was studied by incubating isolated pea thylakoids with phospholipase C to remove the head-group of phospholipid molecules. The treatment was effective in eliminating 40-50% of chloroplast phospholipids and resulted in a drastic decrease of photosynthetic electron transport. Measurements of whole electron transport (H2O→methylviologen) and Photosystem II activity (H2O→p-benzoquinone) demonstrated that the decrease of electron flow was due to the inactivation of Photosystem II centers. The variable part of fluorescence induction measured in the absence of electron acceptor was decreased by the progress of phospholipase C hydrolysis and part of the signal could be restored on addition of 3-(3',4'-dicholorophenyl)-1,1-dimethylurea. The B and Q bands of thermoluminescence corresponding to S2S3QB (-) and S2S3QA (-) charge recombination, respectively, was also decreased with a concomitant increase of the C band, which originated from the tyrosine D(+)QA (-) charge recombination. These results suggest that phospholipid molecules play an important role in maintaining the membrane organization and thus maintaining the electron transport activity of Photosystem II complexes.