β-Carotene Production and Its Role in Sclerotial Differentiation of Sclerotium rolfsii

Abstract

The fungus Sclerotium rolfsii produces β-carotene, the main detected carotenoid, in levels dependent upon oxidative growth conditions and upon differentiation. β-Carotene accumulation is 5-, 6.5-, and 6.7-fold higher in undifferentiated mycelia, sclerotia, and differentiated mycelia, respectively, at high than at low oxidative stress. It accumulates more in older than in younger mycelia and is 2-fold higher in differentiated than in undifferentiated mycelia. We propose that β-carotene is formed possibly to help the fungus reduce oxidative stress that develops during growth. This is supported by the finding that exogenous β-carotene at non-growth-inhibiting concentrations causes a concentration-dependent reduction of oxidative stress (lipid peroxidation) of undifferentiated mycelia, which results in an equally proportional reduction of sclerotial differentiation. The data of this study support our hypothesis that sclerotial differentiation is induced by oxidative stress.