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A method for testing the purity of isolated vacuoles is proposed. Preparations of isolated vacuoles often contain "impure vacuoles," namely, vacuoles contaminated with some cytoplasmic remnants. Such impure vacuoles are stained by the vital fluorescent dye fluorescein-diacetate. Vacuoles enclosed only by the tonoplast, "naked vacuoles," do not stain.
Admon et al. (Tue,) studied this question.