Differentiation and Hydrogen Peroxide Production in Sclerotium rolfsii Are Induced by the Oxidizing Growth Factors, Light and Iron

Abstract

Hydrogen peroxide is produced by Sclero- tium rolfsii during sclerotial differentiation, in re- sponse to oxidative growth conditions of light and Fe. An additive effect of (? light ? Fe)-induced oxida- tive stress is observed on H202 production levels and on sclerotia numbers during fungal development. High H202 production rates are correlated with high oxidative stress and are observed in less lipid-perox- idized young mycelia and sclerotia (sclerotia initials and early developing sclerotia) and not in differen- tiated, highly lipid-peroxidized older mycelia and sclerotia (developed and mature sclerotia). H202 production by undifferentiated mycelia and their ex- posure to exogenous H202 show a rate/dose-depen- dent correlation with degree of sclerotial differenti- ation (sclerotia numbers). Hydrogen peroxide and lipid peroxide concentration gradients are observed in fungal colonies during their transition from un- differentiated (mycelial) to differentiated (sclerotial) stage. Growth-stage-dependent changes in H202 pro- duction rates during development are not due to changes in glucose concentration and pH of the growth medium. Light/Fe-induced H202 production and its effect on S. rolfsii differentiation, are dis- cussed in the context of our hypothesis of oxidative stress-induced sclerotial differentiation.