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 e lectron transport activities was studied by incubating isolated pea th ylakoids with phospholipase C to remove the head-group of phospholipid molecules. The treatment was effective in eliminating 40-50% of chlor oplast phospholipids and resulted in a drastic decrease of photosynthe tic electron transport. Measurements of whole electron transport (H2O --> methylviologen) and Photosystem II activity (H2O --> p-benzoquinon e) demonstrated that the decrease of electron flow was due to the inac tivation of Photosystem II centers. The variable part of fluorescence induction measured in the absence of electron acceptor was decreased b y the progress of phospholipase C hydrolysis and part of the signal co uld be restored on addition of 3-(3',4'-dicholorophenyl)-1,1-dimethylu rea. The B and Q bands of thermoluminescence corresponding to S(2)S(3) Q(B)(-) and S(2)S(3)Q(A)(-) charge recombination, respectively, was al so decreased with a concomitant increase of the C band, which originat ed from the tyrosine D(+)Q(A)(-) charge recombination. These results s uggest that phospholipid molecules play an important role in maintaini ng the membrane organization and thus maintaining the electron transpo rt activity of Photosystem II complexes.