Rhodanine (2-thioxo-4-thiazolidinone) and 2(5H)-thiophenone inhibit germination and root growth of several plants. Using Scenedesmus acutus and Marchantia polymorpha L., these compounds were assayed with respect to degradation of chlorophyll, light-induced ethane formation and growth inhibition to determine the action mechanism. Chlorophyll reduction and growth inhibition of liverwort cells were quantitatively correlated with light-induced ethane formation of Scenedesmus in the presence of these compounds. Furthermore, we found that rhodanine itself decreased the chlorophyll content in liverwort cells and produced ethane with Scenedesmus cells in the light although no protoporphyrin IX (PPIX) accumulated. Diuron did not influence ethane formation with these two compounds as is observed with peroxidizing herbicides like oxyfluorfen. Apparently, rhodanine prevents PPIX accumulation by AFM.

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