[Toxicological effects of omethoate on leaf photosystem II of cole]

After spraying different concentrations of two brands pesticide omethoate on cole (Brassica campestris L.) leaves, the leaf chlorophyll a fluorescence transients were measured by a Plant Efficiency Analyzer (PEA), and the toxicological effects and rudimental dynamic courses of omethoate on the leaf photosystem II (PS II) were investigated by JIP-test. The results showed that after spraying omethoate except at the concentration of 0.50% , the maximal efficiency of photochemistry (F(v)/F(m)) did not have a remarkable change. However, with increasing omethoate concentration, the minimal fluorescence F(o), maximal fluorescence F(m), relative variable fluorescence at the J-step (V(J)), and electron transport flux perreactive center in PS II (ET(o)/RC) increased remarkably, but psi(o), the efficiency that a trapped exciton in PS ]I moved an electron into the electron transport chain beyond Q(A)-, decreased remarkably. The test two brands of pesticide omethoate had almost alike effects on the PS II of cole, and the residual effect of the pesticide was the strongest at the third day after spraying and petered out from the ninth to twelfth day. The main targets of omethoate on the PS II of cole could be listed as promoting the reduction from Q(A) to Q(A) (-) (increasing of V(J)) and the electron transmission from Q(A) (-) to Q(B) (increasing of ET(o)/RC).