Differentiation and hydrogen peroxide production in Sclerotium rolfsii areinduced by the oxidizing growth factors, light and iron

Hydrogen peroxide is produced by Sclerotium rolfsii during sclerotial diffe rentiation, in re; sponse to oxidative growth conditions of light and Fe. A n additive effect of (+/- light +/- Fe)-induced oxidative stress is observe d on H2O2 production levels and on sclerotia numbers during fungal developm ent. High H2O2 production rates are correlated with high oxidative stress a nd are observed in less lipid-peroxidized young mycelia and sclerotia (scle rotia initials and early developing sclerotia) and not in differentiated, h ighly lipid-peroxidized older mycelia and sclerotia (developed and mature s clerotia). H2O2 production by undifferentiated mycelia and their exposure t o exogenous H2O2 show a rate/dose-dependent correlation with degree of scle rotial differentiation (sclerotia numbers). Hydrogen peroxide and lipid per oxide concentration gradients are observed in fungal colonies during their transition from undifferentiated (mycelial) to differentiated (sclerotial) stage. Growth-stage-dependent changes in H2O2 production rates during devel opment are not due to changes in glucose concentration and pH of the growth medium. Light/Fe-induced H2O2 production and its effect on S. rolfsii diff erentiation, are discussed in the context of our hypothesis of oxidative st ress-induced sclerotial differentiation.