Effects of the Fusarium solani toxin dihydrofusarubin on tobacco leaves and spinach chloroplasts

The effects of the Fusarium solani toxin dihydrofusarubin on tobacco leaves and on spinach chloroplasts have been studied in comparison with the herbicide methylviologen. Toxin treatment of tobacco leaves and leaf discs resulted in a light dependent chlorophyll degradation and a simultaneous ethane production. Experiments with spinach chloroplasts showed that dihydrofusarubin interacted with the electron transport chain, thus forming reactive oxygen species. Experiments with DCMU and DBMIB proved that superoxide was produced on photosystem I in a light dependent reaction. Furthermore, we showed that NADPH formation was blocked by dihydrofusarubin. Inhibition started with 10 μmol/L DHF, whereas about 80% inhibition of NADP⁺-reduction was achieved with 100 μmol/L toxin. Inhibition of NADPH-formation was accompanied by a simultaneous increase in ATP-production. Experiments with methylviologen proved that the effects of the Fusarium solani toxin dihydrofusarubin on chloroplasts were comparable with the effects of this herbicide. The significance of the dihydrofusarubin toxin for symptom development on citrus trees infected with Fusarium solani is discussed.