The role of phospholipids in regulating photosynthetic electron transport activities: Treatment of chloroplasts with phospholipase A 2

Abstract

The involvement of phospholipids in the regulation of photosynthetic activities was studied by incubating isolated pea chloroplasts with phospholipase A 2 to remove the β-positioned fatty acyl chains of the phospholipid molecules. The treatment was effective in eliminating 50% of phosphatidylglycerol (PG) and 90% of phosphatidylcholine (PCh) of the chloroplast thylakoids, but it resulted in only a partial decrease in photosynthetic electron transport activities. As found by fluorescence induction measurements the decrease in the electron flow activity was due to the inactivation of about 20% of photosystem II (PSII) centres. However, the fluorescence induction kinetics of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU) poisoned chloroplasts showed that the number of PSII β-like centres was proportionally increased in the membrane by the progress of phospholipase A 2 treatment, suggesting that phospholipid molecules may play an important role in regulating the association of peripheral chlorophyll a/ b containing light-harvesting complex (LHCII-peripheral) with PSII α. The specific involvement of PG and PCh in the organization and function of PSII is discussed.