A HIGH-SENSITIVITY CHLOROPHYLL FLUORESCENCE ASSAY FOR MONITORING HERBICIDE INHIBITION OF PHOTOSYSTEM-II IN THE CHLOROPHYTE SELENASTRUM-CAPRICORNUTUM - COMPARISON WITH EFFECT ON CELL-GROWTH

A pulse amplitude modulated fluorometer (PAM) was used to measure the chlorophyll fluorescence induction kinetics (OIDP). The increase of I level, recorded at two different excitation light intensities, was use d to monitor atrazine, simazine, diuron and isoproturon. The methods u sed were applied to a, sensitive chlorophyte, Selenastrum capricornutu m. Concentrations of about 0.01 mu M of diuron, 0.04 mu M of isoprotur on and atrazine and 0.08 mu M of simazine can be detected significantl y. I-50-values obtained by the most sensitive method, corresponding to an excitation light intensity of 130 mu mol photon . m(-2) . sec(-1), are 0.3 mu M for atrazine, 0.5 mu M for simazine, 0.05 mu M for diuro n and 0.2 mu M for isoproturon. The inhibition of S. capricornutum gro wth over a 4 days period was also studied and the I-50 obtained were a bout 0.4 mu M for-triazines, 0.03 mu M for diuron and 0.2 mu M for iso proturon.