The Role of Membrane Structure in Acclimation to Low-Temperature Stress

All photosynthetic protein complexes are embedded in membranes, and lipids surround these complexes. These lipids are indispensable not only in maintaining the functional state/conformation of the photosynthetic reaction centers, but are also needed for protection against environmental stress conditions such as cold and chilling. The redox enzymes, elements of the photosynthetic electron transport chain, which transform the physical energy of the photons to chemical potential, are also in the photosynthetic complexes. During low-temperature stress conditions, the rate of photosynthetic electron transport decreases. This decrease can be enhanced further by exposing the photosynthetic apparatus to high light-intensities. In this chapter, we concentrate on the role of the photosynthetic membrane, especially on the structural aspects of the lipids involved in the protection against low-temperature stress. Genetic manipulations of higher plants and cyanobacteria have suggested that unsaturation of lipids plays an important role in preserving photosynthetic functions at low temperatures. Lipids, in particular phosphatidylglycerol, the only phospholipid among the components of the photosynthetic membrane, seem to be active partners of the proteins in the adaptive response to low-temperature stress. In addition to lipids, carotenoids, by exerting local effects, may also participate in membrane dynamics-based protective mechanisms. Fourier transform infrared spectroscopy has proven to be a valuable tool to reveal protein secondary structure/dynamics, and lipid conformation. Since in the infrared spectrum the regions characteristic mostly for proteins or lipids are well separated, infrared spectroscopy is a method of choice to reveal structural and dynamic changes, as well as lipid-protein interactions in the photosynthetic membranes during low-temperature stress conditions.