Circadian oscillation and light-induced changes in the concentration of cyclic nucleotides in Neurospora

Summary

Rhythmic oscillations in the concentration of cAMP in myeclia of wild type 74A, bd, bd frq-1 and bd frq-2 strains of Neurospora crassa grown in liquid media in darkness were detected. The period lengths of the rhythm of cAMP concentrations were about 21 to 22 h in 74A and bd, and 14≈20 and 19 h in bd frq-1 and bd frq-2. The concentration of cGMP oscillated slightly. In parallel experiments using solid medium, conidiation occurred about 22 h after the peak of cAMP concentration. Exposure of bd mycelia to white light (3.9 J/m² ·s) at 7∼12 h after the onset of continuous darkness, when the concentration of cAMP was high, reduced the concentrations of CAMP and cGMP, whereas after 18 h of darkness when the concentration of CAMP was low, only the concentration of cGMP was reduced. The reduction in the concentrations of cAMP and cGMP by light occurred within 60 s. Exposure of mycelia to constant light resulted in an oscillation of cAMP concentration with a period length from 60 to 90 min. After 9 h of continuous darkness, exposure of bd mycelia to 0.5 mM cAMP or 0.5 mM cGMP for 1 h and subsequent transfer to solid media resulted in phase advances of the conidiation rhythm of 2.1 h and 1.2 h, respectively. Exposure to light for 1 h, however, caused a 4.3 h phase delay. These results strongly suggest that cAMP and possibly cGMP are factors controlling the circadian rhythm.