Visualization of mitochondria and nuclei in living plant cells by the use of a potential‐sensitive fluorescent dye

Cationic potential‐sensitive dyes have previously been used to selectively stain mitochondria in living animal cells (Johnson, Walsh & Chen, 1980; Johnson et al., 1981). The present work demonstrates that the cyanine dye 3,3′‐dihexyloxacarbocyanine iodide (DiOC6(3)) can also be used as a mitochondrial stain in living plant cells. The stained mitochondria were easily visualized by fluorescence microscopy. The accumulation of DiOC6(3) in mitochondria seemed to be potential‐dependent since it was prevented by protonophores, valinomycin and inhibitors of electron transport. It was often observed that DiOC6(3) also stained the nuclear membrane of some cells. This fluorescence, limited to the perinuclear region, was possibly due to a potential across one or both nuclear membranes, although it was not completely dissipated by any of the ionophores or inhibitors tested. Our observations demonstrate the usefulness of using DiOC6(3) for studying relative membrane potentials of plant mitochondria and, perhaps, other organelles and membrane systems in living plant cells.