Phospholipid Motional Characteristics in a Dry Biological System

Analysis of the proton-decoupled (31)P-nuclear magnetic resonance (NMR) spectrum of fully hydrated Typha latifolia pollen revealed the presence of two main peaks: A broad asymmetrical component of a ;bilayer' lineshape and a much narrower symmetrical component originating from phosphorus compounds undergoing rapid isotropic motion. From (a) (31)P-NMR experiments on the hydrated total pollen phospholipids, (b) saturation transfer (31)P-NMR experiments, and (c) the fraction of lipid phosphate in the pollen, it can be concluded that the great majority of the endogenous phospholipids are arranged in extended bilayers in which the lipid phosphates undergo fast (tau(c) < 10(-6) second) long axis rotation. This bilayer arrangement of phospholipids was observed in the pollen down to hydration levels of at least 10.9% moisture content. At the lowest level of pollen hydration examined (5.2%) the (31)P-NMR spectrum had a solid state lineshape demonstrating that all the phosphorus-containing compounds (including the phospholipids) were virtually immobile.