The role of phospholipids in the molecular organisation of pea chloroplast membranes. Effect of phospholipid depletion on photosynthetic activities

Pea chloroplasts were treated with phospholipase A₂ which hydrolysed approx. 75% phosphatidylglycerol and 60% phosphatidylcholine. The major effect of the treatment was an inhibition of Photosystem (PS) II electron transport together with an (approx. 30%) increase of initial chlorophyll fluorescence (F₀) and a subsequent loss of variable fluorescence during induction, as well as an inhibition of the cation-induced rise in steady-state chlorophyll fluorescence. In contrast to the effects upon PS II activities, PS I activity was not depressed and increased slightly under certain conditions, while the coupling factor for photophosphorylation was inhibited to some extent. No significant increase in spillover was observed following the treatment with phospholipase A₂. These results are discussed in relation to the ways in which phospholipid depletion may lead to the various effects observed. It is proposed that the site of PS II inhibition after phospholipase A₂ treatment may be at the electron transfer from pheophytin to Q, the first quinone-type electron acceptor.