Variation in effects of four OP insecticides on photosynthetic pigment fluorescence of Chlorella vulgaris Beij

Effects of the insecticides quinalphos, chlorfenvinphos, dimethoate and phorate on photosystem activity of Chlorella vulgaris were investigated by different chlorophyll fluorescence measurements. Exposure to each of the insecticides increased the proportion of inactivated PS II reaction center. Quinalphos and chlorfenvinphos caused OJIP fluorescence reduction at all levels by decreasing the proportion of QA-reducing PS II reaction centers (RCs). The other two insecticides affected OJIP fluorescence rise by hindering the electron transport beyond QA. Insecticide treatment resulted in decrease of the density of active RC and performance indices (PI) by enhanced dissipated energy flux per active RC. Antenna size was severely minimized by quinalphos and chlorfenvinphos treatment whereas other two insecticides had no such effect. Each insecticide treatment caused increase of photosystem antenna/core and PS II/PS I fluorescence ratios. Quinalphos and chlorfenvinphos affected the donor sides of photosystems whereas dimethoate and phorate inhibited electron transfer beyond QA (acceptor side).

Research Highlights
► OP insecticides, quinalphos, chlorfenvinphos, dimethoate, and phorate altered OJIP fluorescence rise of Chlorella vulgaris.
► Quinalphos and chlorfenvinphos have the highest effect in J–I fluorescence rise.
► The stress indicating fluorescence parameters showed concentration dependent increase.
► Dimethoate and phorate have herbicide like action on PS II.
► Quinalphos and chlorfenvinphos inhibited PS fluorescence by dissociation of LHC.