Growth, macromolecular syntheses and organophosphate insecticide metabolism in Dictyostelium discoideum exposed to insecticides and ultraviolet light

Abstract

Survival studies performed on the Ax-2 strain of Dictyostelium discoideum demonstrated that the vegetative cells were resistant to UV light at 254 nm. The survival curve began with a broad shoulder and eventually declined exponentially. The D₃₇ value was 880 ergs/nm². Malathion (5 and 10 ppm), malaoxon (10 ppm), and Guthion (1 and 5 ppm) when incorporated into agar plates, exhibited no effect on survival whereas 10 ppm Guthion decreased the number of plaques formed. Experiments were conducted in liquid cultures on the effects of UV radiation (1027, 771, and 515 ergs/nm²) and/or malathion and Guthion at 5 and 10 ppm on growth and macromolecular syntheses of the amoeboid stage. Amoebae exposed to radiation alone showed a division delay dependent on the UV dose, but the lag period was not characterized by total cessation of growth. Once logarithmic growth resumed, growth and macromolecular syntheses rates did not attain control values. Vegetative cells incubated with 5 and 10 ppm malathion or 5 ppm Guthion exhibited no delay periods while amoebae exposed to 10 ppm Guthion did. Like irradiated cells, amoebae added to liquid cultures containing either malathion or Guthion at 5 or 10 ppm never resumed doubling and incorporation times at the same rate as the control. Guthion at 10 ppm inhibited growth and macromolecular syntheses to the greatest extent while 5 ppm malathion had the least effect. When 10 ppm Guthion or 10 ppm malathion were added to irradiated amoebae (1027, 771, and 515 ergs/nm²), a potentiated synergistic effect was observed on both growth and macromolecular syntheses with the greatest influence found at the highest UV dose in presence of Guthion..