Electron tomography of plant thylakoid membranes.

For more than half a century, electron microscopy has been a main tool for investigating the complex ultrastructure and organization of chloroplast thylakoid membranes, but, even today, the three-dimensional relationship between stroma and grana thylakoids, and the arrangement of the membrane protein complexes within them are not fully understood. Electron cryo-tomography (cryo-ET) is a powerful new technique for visualizing cellular structures, especially membranes, in three dimensions. By this technique, large membrane protein complexes, such as the photosystem II supercomplex or the chloroplast ATP synthase, can be visualized directly in the thylakoid membrane at molecular (4-5 nm) resolution. This short review compares recent advances by cryo-ET of plant thylakoid membranes with earlier results obtained by conventional electron microscopy.