The formation of reactive oxygen species by fungal and bacterial phytotoxins

Several microbial phytotoxins are known to induce the formation of reactive oxygen species (ROS). This review points out the different mechanisms by which oxygen activation takes place: photodynamic formation of singlet oxygen as well as reductive activation of oxygen via photosynthetic electron transport, diaphorases, cytochrome P450 and dithiols. Particular emphasis is put on the naphthazarin toxins from Fusarium solani which were shown to reductively activate oxygen via several mechanisms. The significance of oxygen activation by phytotoxins for symptom development is discussed.