Enhancement of chlorophyll a fluorescence yield, low-temperature F685/F730 fluorescence emission ratio, and electron transport rate by ether phospholipids (platelet activating factor and analogs) in isolated chloroplasts

Acetyl glyceryl ether phosphorylcholine (1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine; or platelet activating factor (PAF)), when incubated with chloroplasts or subchloroplast fractions derived from stroma or grana lamellae, induces a drastic increase in the low-temperature fluorescence emission ratio F685/F730 (77 degree K). The molecular structure requirement for the effect to be elicited is the ether bond and a long C chain at the C-1 position of glycerol, a short C chain at C-2 (or the lyso form), and a large polar head at C-3, the potent effector being PAF C-16. The effect is more pronounced in grana-derived fractions. PAF also induces an increase in the chlorophyll alpha fluorescence yield, enhances the association of chlorophyll in the supramolecular pigment-protein complexes of the thylakoid (especially those of Photosystem II), and enhances electron transfer from 1,5-diphenyl carbazide to 2,6-dichlorophenol. These effects are attributed to alteration of the Photosystem II unit organization via the incorporation/intercalation in the grana of the wedge-shaped PAF.