A hyperoxidant state at the start of each developmental stage during Neurospora crassa conidiation

RESUMO

Neurospora crassa conidiation and other microorganism differentiation processes can be explained as a response to a hyperoxidant state. Many proteins, among them NADP-glutamate dehydrogenase and glutamine synthetase, were oxidatively modiried and degraded at the start of all three morphogenetic transitions of the conidiation process. A shift in the redox state of the main cellular electron carriers, from a highly reduced state to a predominantly oxidized one, occurred stepwise with a highly oxidizing event at the start of each transition. Catalase activity increased during cell differentiation in various microorganisms and one of two catalases accumulated to a high level in the differentiated cell. Catalases in Neurospora were oxidized in vitro and in vivo giving rise to active enzyme conformers. Carotenoids, which have antioxidant functions in fungi, were consumed in each morphogenetic stage and oxidized carotenoids accumulated in differentiated cells. Carotenoid biosynthesis was induced following oxidative stress and during conidiation in each new cell structure. Increased generation of reactive oxygen species was detected by chemiluminescence at the onset of all transitions during differentiation. Antioxidants inhibited both light emission and cell differentiation. These and other data from the literature are discussed in the context of the Dioxygen Avoidance Theory of cell differentiation.