Phosphatidylinositol monophosphate in Lilium pollen and turnover of phospholipid during pollen tube extension Johannes P.F.G. Helsper

Abstract

A considerable incorporation of [32P]orthophosphate into phospholipids was observed during germination of pollen of Lilium longiflorum, particularly during the period of most rapid pollen tube elongation. The major phospholipids were phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol and phosphatidic acid. The amount of lipid-bound phosphorus (0.05 μmol/mg pollen) did not change significantly during germination, suggesting that the incorporation was mainly due to turnover. myo-[2-3H]Inositol was incorporated into phospholipids as well as into pectic cell wall polysaccharides. The phospholipids labelled with both 3H and 32P were found to be phosphatidylinositol (90% of 3H-label) and phosphatidylinositol monophosphate. The identity of the latter was established by thin layer chromatography, by anion exchange column chromatography (with immobilized neomycin sulphate as the stationary phase), and by the formation of glycerylphosphoryl inositol phosphate and inositol bisphosphate during alkaline hydrolysis. Pulse-chase experiments suggested that about 40% of the myo-inositol moieties in phosphatidylinositol is exchanged during the 4 hr-period of most rapid pollen tube extension. This high figure may be a consequence of membrane flow known to take place during pollen tube elongation, proceeding at the high rate of approximately 1 mm/4 hr. Phosphatidylinositol phospholipase C activity, which could play a role in this turnover, was detected in pollen tube homogenates. Phospholipase activities towards the other major phospholipids were also observed.