Photoswitching of mOrange2 fluorescent protein. The chloroplast division protein FtsZ2 tagged with mOrange2 was expressed in yeast and imaged using Olympus FV1000 confocal microscope. Repeated excitation with 543 nm laser drives the fluorescent protein to dark state and the fluorescence signal declines. The sample was then illuminated with 405 nm laser which converts mOrange2 from the dark state to the fluorescence-capable state, leading to elevated fluorescence signal at the beginning of the next excitation sequence. Image by Stanislav Vitha, MIC.