IRON UPTAKE IN USTILAGO-MAYDIS - STUDIES WITH FLUORESCENT FERRICHROMEANALOGS

Iron uptake by the phytopathogenic fungus Ustilago maydis was studied using synthetic biomimetic ferrichrome analogues and their fluorescent ly labelled derivatives as structural and dynamic probes, respectively . The use of structurally distinct analogues enabled determination of the structural requirements for recognition by the fungal iron-uptake system. The application of fluorescently labelled derivatives which co nvert from a nonfluorescent to a fluorescent state upon iron (III) rel ease enabled monitoring of iron uptake in real time both fluorimetrica lly and microscopically. Different rates of Fe-55 uptake were found fo r two structurally distinct synthetic analogues, B9 and B5, which diff er in their amino acid building blocks. B9 mediated uptake of Fe-55 at a higher rate than B5. The behaviour of the fluorescent derivatives B 9-Ant (anthracene-labelled B9) and B5-Ant (anthracene-labelled B5) par alleled that of their non-labelled precursors. Exposure of fungal cell s to BS-Ant led to a higher increase of fluorescence in the medium tha n exposure to BE-Ant, indicating a more effective iron uptake from BE- Ant. By using fluorescence microscopy it was possible to trace the lab el of BE-Ant. Fluorescence was localized in regularly shaped vesicles in the treated cells, The rate of fluorescence appearance within the c ells lagged behind the rate of iron uptake, suggesting use of the side rophores for iron storage.