Phytotoxic and photosynthetic activities of maduramicin and maduramicin methyl ester

The polyether antibiotic maduramicin and its methyl ester derivative inhibi ted photophosphorylation and proton uptake in isolated spinach chloroplasts . Both compounds also enhanced basal and phosphorylating electron transport and stimulated Mg2+-dependent ATPase activity, therefore, they behave as u ncouplers of photophosphorylation being the methyl ester derivative more po tent than the parent compound. On the other hand, maduramicin inhibited ger mination and radicle elongation of several crop and weed species. In additi on, the antibiotic caused phytotoxic injury and fresh weight reduction to 4 -to-6 week old seedlings of two weed and two crop species when applied at 1 0(-4) M by foliar application in the greenhouse.