Summary: We report initial attempts to define the role of Ca in the polarized extension of Growth of the organism was diminished in media containing less than 1 m-Ca; extension was more severely impaired than biomass synthesis, resulting in the formation of stubby, bulbous hyphae, even of spherical cells. Reduced extension and abnormal morphology were correlated with the loss of surface-bound Ca, probably associated with the cell wall. Intracellular Ca may be represented by material that fluoresces brightly in the presence of chlortetracycline. Punctate fluorescent bodies and diffuse fluorescence were both arrayed in a longitudinal gradient, maximum apically. Addition of the calcium ionophore A23187 induced dissipation of the fluorescence; concurrently, the hyphae lost as much as one half of their Ca content. Extension continued almost unabated, but multiple branches quickly emerged from the apex. The observations suggest that a cytoplasmic Ca gradient is not required for polarized extension, but may play a role in ensuring the dominance of the apex.


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