Visualization of the cytoplasmic Ca2+ gradient in Fucus serratus rhizoids: Correlation with cell ultrastructure and polarity

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Abstract
Fura-2 has been used with digital image analysis to visualize and quantify the cytoplasmic Ca2+ gradient in rhizoid cells of Fucus serratus. Ca2+ was higher at the growing rhizoid tip in about 50–60% of cells studied to date. Considerable variation in the pattern of the Ca2+ gradient has been found. Verapamil reduced but did not abolish the Ca2+ gradient. Nifedipine had no effect on Ca2+ distribution during the experimental period. Removing Ca2+ from the growth medium permeabilized the plasmalemma and allowed fura-2 to efflux from the cytoplasmic compartment, permitting an assessment of the degree of sequestration of the dye into vacuoles and vesicles. Comparisons of ratio images with electron micrographs suggested that lower Ca2+ levels were associated with the nuclear region, but there was no direct correlation between Ca2+ levels and vesicle distribution in healthy cells. The role of localized differences in Ca2+ distribution in the control of polarity is discussed.