The chlorophyll fluorescence (CF) assay is recognized as an important tool for monitoring the electron transport system of photosynthesis. The increase or decrease of fluorescence, compared to control, can indicate a lesion in the chain of events in photosynthesis or damage to the chloroplasts. Inhibition of photosynthesis in leaf segments of Tradescantia by herbicides (glyphosate, picloram & 2,4-D, triclopyr and hexazinone), heavy metals (Zn, Cu, Cd), a surfactant (sodium lauryl sulfate), and sodium fluoride (NaF) has been demonstrated using this method. The strongest changes of fluorescence induction curves were caused by hexazinone. Photosynthetic inhibition was observed as an increase in initial fluorescence (Fo) and a decrease in variable fluorescence (Fv) and electron pool size (EP). A CF assay predicted herbicidal injury in Tradescantia leaves at least 24 h before leaf necrosis appeared.
Three heavy metals (Zn, Cu, Cd) are known as strong respiration and photosynthetic inhibitors in plant cells. In this study cadmium chloride, at the highest concentration (1000 ppm) tested, caused the strongest changes in Fv and EP size, which are characteristics of Photosystem II (PS II) photochemistry. Phytotoxicity of NaF caused an increase in Fv and EP compared to the control.