Flow cytometry as a tool to study phytotoxic modes of action

The objective of the present investigation was to provide a diagnostic tool for the analysis of phytotoxic interactions between environmental contaminants and algae by application of flow cytometry. Therefore, an experimental design was developed consisting of synchronized Scenedesmus vacuolatus cell populations at defined cell-cycle stages, short-term exposure against different inhibitors with known molecular targets, and fluorochrome labeling of different metabolic processes. To discriminate cells with compromised metabolic processes from intact and metabolically inactive cells, references for every fluorochrome were defined using control and heat-treated populations. The experimental results showed that fluorescence markers are able to detect disturbance of specific cellular characteristics, such as membrane integrity, chlorophyll synthesis, and degradation. A differentiation of impacts on specific metabolic process caused by the reference inhibitors in concentration-dependent patterns could be seen using flow-cytometric fluorochrome analysis. These findings were compared with effects observed for N-phenyl-2-naphthylamine (PNA), a sediment contaminant of high phytotoxicity but unclear mode of action. Rhodamine 123 and cyano-ditolyl tetrazolium chloride detected significant metabolic changes for relevant exposures against PNA, thus pointing to compromised mitochondrial activity and changes in membrane potential as causes of phytotoxicity.