Cell size specific binding of the fluorescent dye calcofluor to budding yeast

Abstract

The yeast Saccharomyces cerevisiae cell surface outside of the bud scars displayed an increasing fluorescence intensity with increasing cell size (volume), where fluorescence was due to irreversible binding of the fluorescent dye calcofluor. The increase in fluorescence intensity appeared to be due to an increase in the density of fluorescence per unit surface area of the cell. Exposure time measurements form a photomicroscope were used to quantitate fluorescence intensity on individual cells. The cell size dependent increase in fluorescence intensity was displayed by unbudded cells from stationary phase populations, and unbudded and parent cells from exponentially growing populations. Abnormally large cells generated during the arrest of cell division with α-factor or restrictive temperature for cdc3, 8, 13, 24, and 28 cell division cycle mutants, displayed significantly greater fluorescence intensity compared to the smaller cells generated during the arrest of division for cdc25, 33, and 35 mutant strains. Fluorescence intensity on newly emerging buds was broadly dependent on both the size of the bud, and the size of the parent cells on which the buds were growing.