The role of lipids in the structure and function of photosynthetic membranes

Enhanced thermal stability of the thylakoid membranes from spruce. A comparison with selected angiosperms

Recently, we have found that thermal stability of photosystem II (PSII) photochemistry in spruce needles is higher than in other plants (barley, beech) cultivated under the same temperatures. In this work, temperature dependences of various characteristics of PSII organization were studied in order to obtain complex information on the thermal stability of PSII function and organization in spruce. Temperature dependency of circular dichroism spectra revealed by about 6 °C higher thermal stability of macrodomain organization in spruce thylakoid membranes in comparison with Arabidopsis and barley ones; however, thermal disintegration of light-harvesting complex of PSII did not significantly differ among the species studied. These results thus indicate that thermal stability of PSII macro-organization in spruce thylakoid membranes is enhanced to a similar extent as thermal stability of PSII photochemistry. Clear-native polyacrylamide gel electrophoresis of preheated thylakoids demonstrated that among the separated pigment-protein complexes, only PSII supercomplexes (SCs) revealed considerably higher thermal stability in spruce thylakoids as compared to Arabidopsis and barley ones. Hence we suggest that higher thermal stability of PSII macro-organization of spruce is influenced by the maintenance of PSII SCs in the thylakoid membrane. In addition, we discuss possible effects of different PSII organizations and lipid compositions on the thermal stability of spruce thylakoid membranes.

Phosphatidylcholine-induced reactivation of photosystem II membranes pretreated with Triton X-100

Triton X-100-induced inactivation and phosphatidylcholine-induced reactivation of photosystem II (PSII) membranes were investigated using oxygen electrode, variable fluorescence and spectroscopic techniques including absorption and circular dichroism spectroscopy. Incubation of the PSII membrane with Triton X-100 reduced the oxygen-evolving rate, modified the variable chlorophyll fluorescence kinetics, changed the protein secondary structures, altered the chlorophyll binding state to proteins and decreased the excitonic interaction of chlorophyll molecules. Phosphatidylcholine addition did not change the protein secondary structures, but could partially reactivate the reduced oxygen-evolving rate, and partly reversed the variable fluorescence parameters, the chlorophyll binding state and the excitonic interaction of the chlorophyll molecules. The results indicate that the phosphatidylcholine environment can optimize the tertiary structures of PSII.

Strong-light photoinhibition treatment accelerates the changes of protein secondary structures in triton-treated photosystem I and photosystem II complexes

Changes in the protein secondary structure and electron transport activity of the Triton X-100-treated photosystem I (PSI) and photosystem II (PSII) complexes after strong illumination treatment were studied using Fourier transform-infrared (FT-IR) spectroscopy and an oxygen electrode. Short periods of photoinhibitory treatment led to obvious decreases in the rates of PSI-mediated electron transport activity and PSII-mediated oxygen evolution in the native or Triton-treated PSI and PSII complexes. In the native PSI and PSII complexes, the protein secondary structures had little changes after the photoinhibitory treatment. However, in both Triton-treated PSI and PSII complexes, short photoinhibition times caused significant loss of alpha-helical content and increase of beta-sheet structure, similar to the conformational changes in samples of Triton-treated PSI and PSII complexes after long periods of dark incubation. Our results demonstrate that strong-light treatment to the Triton-treated PSI and PSII complexes accelerates destruction of the transmembrane structure of proteins in the two photosynthetic membranes.