Localization of mitochondria in plant cells by vital staining with rhodamine 123

The positively-charged fluorescent dye rhodamine 123 (r-123) specifically stains mitochondria in living plant protoplasts, suspensionculture cells, and root hairs. This dye functions as a vital stain and permits visualization of the localization, distribution and movement of the mitochondria. Dehydration of root hairs caused mitochondria to aggregate into clumps. Mitochondria were either homogenous or heterogeneous and were frequently seen to accumulate in the perinuclear regions of suspension-culture cells but not in those of protoplasts or root-hair cells. Dinitrophenol and high concentrations of ethyleneglycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid and KCl immediately eliminated fluorescence in r-123-stained mitochondria whereas ionomycin enhanced it. Treatment of seedlings with r-123 resulted in differential brightness of fluorescence in different tissues. Meristematic tissues, such as root and shoot tips, exhibited the brightest fluorescence. The cytotoxicity of r-123 in both germinating seedlings and suspension-culture cells was low. The specificity, sensitivity and low toxicity of r-123 should make it a useful tool in experiments designed to examine agents and conditions which affect the location, the physiological status or the viability of mitochondria.