HEAT-SHOCK EFFECTS ON 2ND-MESSENGER SYSTEMS OF NEUROSPORA-CRASSA

Exposure of growing hyphae of Neurospora crassa to heat shock (44 degr ees C) or ethanol (2.6 M) for 1 h induced a significant increase in th e cAMP level, which reached a maximum approximately 2 min after the be ginning of treatment and then decreased to control values despite cont inued heat or ethanol exposure. A 10-s heat shock or a 5-s ethanol sho ck also resulted in a transient cAMP increase 2 min after the pulse. H eat shock or ethanol treatment led to an increase in the amount of cat alytic subunits of the cAMP-dependent protein kinase A in the nucleus almost synchronously with the increase of cAMP in the cytoplasm. The c oncentration of cGMP decreased a few seconds after the beginning of he at shock (44 degrees C) or ethanol treatment (2.6 M) to approximately 50% of the control level. Exposure to heat shock (44 degrees C, 1 h) l ed to an increase in the amount of inositol phosphates 0.5-2 min after the onset of heat shock. Thereafter, inositol phosphate levels droppe d to control values despite continued heat exposure. Incubation of gro wing hyphae with cAMP or 8-Br-cAMP led to a two- to threefold increase of inositol phosphates 10-300 s after the beginning of incubation. He at treatment furthermore caused a rapid release of calcium from vacuol es as determined by Fura-2 measurement of the calcium content released from isolated vacuoles. These heat-shock-dependent second messenger c hanges may play a role in the heat-shock-induced phase shifts of the c ircadian clock and heat-shock-induced conidiation.