The effect of fluorescent labeling on calcium-induced fusion of fusogenic carrot protoplasts.

Various fluorescent compounds - carboxyfluorescein, scopoletin, fluorescein isothiocyanate (FITC), rhodamine B isothiocyanate (RITC), rhodamine 123, and rhodamine B ethyl ester - were used to study their effects on calcium-induced fusion of fusogenic carrot (Daucus carota L.) protoplasts. These protoplasts normally fused at a high percentage (50-60%) in response to 10 mM calcium, pH 6.0; however, if cells had been labeled with scopoletin, FITC, or RITC, fusion was greatly reduced. In contrast, labeling with carboxyfluorescein, rhodamine 123, or rhodamine B ethyl ester had no detectable effect on calcium-induced fusion. The two rhodamine dyes are shown to be localized in mitochondria.