Calcium as a branching signal in Neurospora crassa.

The divalent cation ionophore A23187 was found to induce apical branching in Neurospora crassa. Optimal effects were obtained by treatment with 0.1 mM ionophore for 30 min. Branching first became manifest during or shortly after treatment; successive rounds of branching could be observed at later times. Calcium starvation of the mycelium markedly reduced its subsequent response to the ionophore, whereas starvation for other divalent cations had no detectable effect. The branching response was markedly reduced in the presence of 10 to 30 mM cyclic AMP or derivatives thereof.