Singlet oxygen is part of a hyperoxidant state generated during spore germination

We show that singlet oxygen is generated in asexual spores (conidia) from N eurospora crassa at the onset of germination. Oxidation of N. crassa catala se-1 (Cat-1) was previously shown to be caused by singlet oxygen (Lledias e t al. J. Biol. Chem. 273, 1998). In germinating conidia, increased protein oxidation, decrease of total protein, Cat-1 oxidation and accumulation of c at-1 mRNA was detected. These changes were modulated in vivo by light inten sity, an external clean source of singlet oxygen, and by carotene amount an d content of coordinated double bonds. Conditions that stimulated singlet o xygen formation increased Cat-1 oxidation and accumulation of cat-1 mRNA. G erminating conidia from mutant strains altered in carotene synthesis showed increased levels of protein degradation, Cat-1 oxidation and accumulation of cat-1 mRNA. During germination Cat-1a was oxidized, oxidized Cat-1c-Cat- 1e conformers disappeared and Cat-1a was synthesized de novo. Furthermore, spontaneous oxygen-dependent chemiluminescence increased as soon as conidia absorbed dissolved oxygen. Low-level chemiluminescence is due to photon em ission from excited electrons in carbonyls and singlet oxygen as they retur n to their ground state. H2O2 added to conidia under Ar caused a peak of ch emiluminescence and germination of 20% of conidia, suggesting that a hypero xidant state suffices to start germination under anaerobic conditions. Take n together, these results show that singlet oxygen is part of a hyperoxidan t state that develops at the start of germination of conidia, in consonance with our proposal that morphogenetic transitions occur as a response to a hyperoxidant state. (C) 1999 Elsevier Science Inc.