3.2 Dynamic distribution, translocation and accumulation of pesticides in cucumber plants
The dynamic distribution and accumulation of CLO, DFN and DFZ in cucumber plants are shown in Fig. 2A under hydroponic experiments. For CLO and DFN, the concentrations of pesticides in leaves were much higher than those in roots and stems, indicating that CLO and DFN were mainly accumulated in leaves, and these have great upward conductivity, respectively. For DFZ, the concentration of pesticide in roots was much higher than that in stems and leaves, indicating that DFZ could be mainly accumulated in roots, and its upward conductivity was poor.
The effects of exogenous SA on the distribution of three pesticides in the roots, stems and leaves of cucumber plants are shown in Fig. 2 B, C, D . From the charts, it can be seen that with SA supplementation the concentrations of three pesticides in roots, stems and leaves of cucumber plants basically showed a decreasing trend during the 28 days of growth. To assess the overall effects of SA on the distribution of three pesticides in different parts of cucumber plants, the mean residues of three pesticides in different parts of cucumber plants after 28 days of growth were calculated, respectively (Fig. 3 ). With SA supplementation at 1mg L-1, the concentration of CLO and DFN in roots and leaves significantly decreased by 27%, 18% and 23%, 19%, respectively, compared with the treatments of CLO and DFN alone; with SA supplementation at 10mg L-1, the concentration of CLO and DFN in roots and leaves significantly decreased by 56%, 28% and 46%, 25%, respectively, compared with the treatments of CLO and DFN alone. With SA supplementation at 50mg L-1, the concentration of CLO in roots and leaves significantly decreased by 23% and 20%, respectively, compared with the treatment of CLO alone. For DFZ, the concentration in roots significantly decreased by 11% and 40% after addition of SA at 1mg L-1 and 10mg L-1, respectively, compared with the treatment of DFZ alone.