Loss of NAD(P)-reducing power and glutathione disulfide excretion at the start of induction of aerial growth in Neurospora crassa

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Abstract
When exponentially growing hyphae of Neurospora crassa in aerated liquid cultures are filtered and the resulting mycelial mat is exposed to air, aerial hyphae develop and synchronous conidiation is obtained. The hyphae in direct contact with air adhere to each other within minutes and form aerial hyphae during the following 12 h; the hyphae which are not in direct contact with air do not adhere to each other and do not form aerial hyphae. Previous data indicated that oxidative stress was generated in the adhering hyphae; proteins and specific enzymes were found to be oxidatively modified and degraded. In this work, we report a dramatic fall in the reduced-to-oxidized ratio of NAD and NADP coenzymes during the first 6 min of exposure to air. This drop did not occur in a mycelial mat exposed to a N2-enriched atmosphere. Adding a carbon source to the mycelial mat did not abolish the loss of NAD(P)-reducing power. After the initial fall, the reducing levels of the coenzymes returned to the starting value in about 30 min. A peak of extracellular glutathione disulfide occurred simultaneously with the loss of NAD(P)-reducing power. The reducing power loss and the excretion of glutathione disulfide are thought to be consequences of a hyperoxidant state; the adhesion of hyphae is thought to be a response to the hyperoxidant state.