Abstract
Changes in both structure and dynamics of thylakoid membranes exposed to heat 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 CH 2 stretching vibration regions providing data on protein secondary structures and lipid acyl chain conformations, respectively. The partitioning of 2,2,6,6,-tetramethylpiperidine-1-oxyl (TEMPO) and chain dynamics of 5-(4′,4′-dimethyloxazolidine-N-oxyl)stearic acid (5-SASL) spin labels in thylakoid membranes were measured using EPR spectroscopy. Both proteins and lipids responded to heat stress with major structural changes around 40°C and 50°C, at any stages of greening, which can be related to the dissociation of the light harvesting complexes and the exclusion of non-bilayer-forming lipids from the membrane, respectively. Greening was found to be a multistage process concerning both mobility, packing density and conformation of lipid fatty acyl chains as well as protein secondary structure, with correlated events during illumination.
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