Fourier transform infrared and electron paramagnetic resonance spectroscopic studies of thylakoid membranes

Changes in both structure and dynamics of thylakoid membranes exposed to he at stress during greening of etiolated barley seedlings were studied using complementary spectroscopic techniques. FTIR spectra of thylakoid membranes were analyzed in the Amide I and the symmetric CH2 stretching vibration re gions providing data on protein secondary structures and lipid acyl chain c onformations, respectively. The partitioning of 2,2,6,6,-tetramethylpiperid ine-1-oxyl (TEMPO) and chain dynamics of 5-(4',4'-dimethyloxazolidine-N-oxy l)stearic acid (5-SASL) spin labels in thylakoid membranes were measured us ing EPR spectroscopy. Both proteins and lipids responded to heat stress wit h major structural changes around 40 degrees C and 50 degrees C, at any sta ges of greening, which can be related to the dissociation of the light harv esting complexes and the exclusion of non-bilayer-forming lipids from the m embrane, respectively. Greening was found to be a multistage process concer ning both mobility, packing density and conformation of lipid fatty acyl ch ains as well as protein secondary structure, with correlated events during illumination. (C) 1999 Elsevier Science B.V. All rights reserved.