GEORGIOU, C.D.; University of Patras: Sclerotial morphogenesis in fungi is induced by oxidative stress

Sclerotium-forming fungi are very important plant pathogens with great biological interest because they can be viewed as models of primitive morphogenesis. They differentiate by asexually producing sclerotia which are usually spherical bodies of aggregated hyphae. In spite of the biological, ecological and agricultural significance of these fungi, the processes involved in their morphogenesis were poorly understood. In 1997, I showed that sclerotium formation in Sclerotium rolfsii was accompanied by high levels of lipid peroxidation, a well-established oxidative stress indicator. This finding prompted me to introduce a hypothesis, supporting that sclerotial morphogenesis is induced by oxidative stress. This theory predicts the following: a) Growth factors that eliminate or promote oxidative stress are expected to inhibit or promote sclerotium morphogenesis, respectively. b) Natural or artificial antioxidants and oxidants that eliminate or promote oxidative stress should inhibit or promote sclerotium morphogenesis, respectively. c) High and low oxidative stress growth conditions should increase and decrease the formation of natural antioxidants, respectively. These assumptions have been verified by a series of published data on the effect of certain hydroxyl radical scavengers on sclerotial morphogenesis, on the identification and quantification of certain natural antioxidants (such as vitamin C, beta-carotene) in relation to the fungal undifferentiated and differentiated stages, and on their effect as growth nutrients on sclerotial morphogenesis. Experiments are underway on the role of glutathione, hydrogen peroxide and superoxide radical on sclerotial morphogenesis. The implications of the oxidative stress-induced sclerotial morphogenesis theory may be extended to the use of antioxidants as non-toxic alternatives to classical fungicides.