Trichlorfon-Induced Inhibition of Nitrate and Ammonium Uptake in Cyanobacteria

The possibility that the primary effect of the toxic insecticide trichlorfon is an inhibition of nitrate uptake in cyanobactena has been investigated. A drastic reduction in the rate of uptake is detected 3 h after the addition of the insecticide to batch cultures of nabaena PCC 7119. The dose-response curves indicate a relationship between the degree of inhibition of nitrate uptake and the reduction of chlorophyll content and growth. Nitrate reductase (ferredoxin : nitrate reductase, EC 1.7.99.4) activity is also lowered as a result of insecticide action. When Anabaena PCC 7119 cells are grown with ammonium as a source of combined nitrogen, trichlorfon reduces the rate of ammonium uptake. The rate of uptake of both nitrate and ammonium is restored upon washing the cells. Ultrastructural analysis of Anabaena nitrate-grown cells shows that trichlorfon does not damage thylakoid membranes, but brings about the accumulation of enlarged cyanophycin granules and the increase of carboxysome number. Nitrate uptake rate and chlorophyll and phycobiliprotein contents are also reduced by insecticide treatment in the cyanobacteria Synechococcus UAM 211, GloeothecePCC 6501, Plectonema calothricoides, Nostoc UAM 205 and Chlorogloeopsis PCC 6912. These results are consistent with the inhibition of nitrate uptake due to weak adsorption of trichlorfon to the plasmalemma being the main effect of the insecticide on cyanobacterial metabolism.