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2341Mutants of the filamentous fungus Neurospora crassa which grow well only in a medium in which the concentration of calcium is lower than in the medium used for culture of the wild-type strain were isolated by use of the ionophore A23187 and medium which contained a high concentration of calcium. These mutants showed a significantly lower uptake of calcium into their vacuoles than the wild-type, while other activities associated with the transport of calcium across several other types of membrane were not affected. The results indicated an essential role for the vacuoles in the regulation of the cytosolic concentration of calcium.

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3-h pulses of elevated temperatures (30 degrees C, 35 degrees C, 40 degrees C) phase shift the circadian conidiation rhythm of Neurospora crassa. The phase and amplitude of the phase response curves (PRC) were measured in wild type (frq+) and frequency mutants (frq 1, frq 7). The dose dependence of the phase shifts was compared to the dose dependence of total protein synthesis inhibition and heat shock protein induction in the three strains. All processes showed an almost linear dependence on temperature. These experiments and other available data suggest that a temperature increase may act on the circadian rhythm by a process belonging to the heat shock response.