EFFECTS OF CYTOCHROME P450-INTERACTING PLANT-GROWTH RETARDANTS, FUNGICIDES AND RELATED-COMPOUNDS ON CELL-DEVELOPMENT AND PHASE-I BIOTRANSFORMATION CAPACITY OF UNICELLULAR PHOTOAUTOTROPHIC GREEN-ALGAE

Fourteen compounds (paclobutrazol, triadimenol, BAS111..W, propiconazo le, tetcyclacis, prochloraz, metyrapone, piperonyl butoxide, 1-aminobe nzotriazole, fenpropimorph, propham, prohexadione, mepiquat chloride a nd chlormequat chloride), most of them established inhibitors of cytoc hrome P450-dependent mixed function oxygenases and used as pesticides, especially plant growth regulators or fungicides, were applied to the non-target organisms Chlorella fusca and Chlorella sorokiniana, two s pecies of photoautotrophic unicellular green algae. The inhibitory pro perties of these compounds were evaluated by comparing concentration/r esponse relationships for the integral parameters of cell volume growt h and cell division with those for the P450-dependent O-dealkylase act ivity measured in vivo using 7-ethoxycoumarin and 7-ethoxyresorufin as xenobiotic model substrates for phase-I biotransformation. The result s obtained indicate a strong algicidal activity for some of these comp ounds, with differential sensitivity of the order: cell division > O-d ealkylation > cell volume increase. EC(50) values for cell division of C. fusca ranged from 0.1 to 9.3 mu mol litre(-1) for prochloraz and p aclobutrazol, respectively. Furthermore, in most cases, concentrations around 10 mu mol litre(-1) limited significantly the capacity for cyt ochrome P450 O-dealkylase activity.