Cyclic AMP level in relation to different conditions of sporulation rhythm regulation in Leptosphaeria michotii (west) Sacc.

When Leptosphaeria michotii was grown in conditions that permitted a stable periodicity of sporulation (asparagine 6.6 mM and in darkness or asparagine 2.6 mM in continuous white light), he level of intracellular cyclic AMP was lower and the activity of the cyclic AMP phosphodiesterase higher in contrast to the cultures with an instable periodicity. With asparagine 6.6 mM and in darkness, theophylline (1 mM) increased the intracellular cyclic AMP level whereas caffeine (1 mM) had no effect. Theophylline (0.01 and 0.1mM) or caffeine (0.01 - 1 mM) provoked a rhythm instability under these conditions. Isoproterenol (1 mM) increased the cyclic AMP level. Nevertheless, the instable rhythm observed in control fed with asparagine 2.6 mM in darkness, was partially stabilized with isoproterenol 0.01 micron or 0.01 - 1 mM. Exogenous cyclic AMP (0.01 - 1 mM) provoked a complete regulation of the rhythm with asparagine 2.6 mM and a shortening of the stable period (from 27 to 21 h) when the fungus was grown on asparagine 6.6 mM. These results underlined the fact that Leptosphaeria rhythm regulation was not dependent on the cyclic AMP level only.