Quantitative assessment of the combined effect of the nitrogen status, light and dehydration of mycelium on conidiation in Neurospora crassa

We performed a quantitative assessment of the conidia yield in Neurospora crassa in response to treatment with different conidiation effectors. Depending on nitrogen source and intactness of nitrite reducetase (NiR) and nitrate reductase (NR), light and dehydration affected the number of viable conidia produced by the ascomycete. In most variants of the nitrogen status, the combined action of light and dehydration synergistically increased the conidia yield. Conidiation in wild-type cells cultivated on the medium with NH4Cl as a sole nitrogen source did not respond to light, whereas illumination of the same culture grown on NH4NO3- or NaNO3-containing medium stimulated the process of spore formation. In response to light exposure, conidia formation occurred in the same way in the nit-2 (no NR and NiR) and nit-6 (no NiR) mutants cultivated in the presence of NH4Cl, but differed greatly when grown on the medium with NH4NO3. The results obtained indicate the possibility that NR and NiR participate in the photoconidiation regulation (wild-type strain on the medium with secondary nitrogen source); however, they cannot be necessary because light-dependent stimulation of spore formation was observed in nit-2 and nit-6 mutants.