Role of erythroascorbate and ascorbate in sclerotial differentiation in Sclerotinia sclerotiorum

Abstract

Sclerotinia sclerotiorum produced erythroascorbate at levels dependent on oxidative growth conditions, developmental stage and strain differentiating capacity. The transition of S. sclerotiorum from the undifferentiated to differentiated state under high oxidative stress growth conditions, was accompanied by a shift in the ratio of reduced/oxidized erythroascorbate towards its oxidized form. At low oxidative stress, the reduced form of erythroascorbate predominated. In a non-differentiating strain of S. sclerotiorum, reduced erythroascorbate predominated over the oxidized form during growth. The reduced/oxidized erythroascorbate ratio in this strain was 5-fold higher than the corresponding ratio in the differentiating strain. The level of oxidative stress (lipid peroxidation) in colonies of the differentiating strain (one day before they differentiated) was 3-fold higher than that formed in colonies of the non-differentiating strain. Exogenous ascorbate exhibited its antioxidant activity in the differentiating strain by causing a dose-dependent decrease in lipid peroxidation, and proportional inhibition of sclerotial development. It is suggested that during its initial growth stages, S. sclerotiorum cannot decrease lipid peroxidation to levels found in the non-differentiating strain, and then forms sclerotia. We propose that oxidative stress triggers differentiation in sclerotium-producing filamentous phytopathogenic fungi.