2.1. Chemicals and materials
Certified pesticide standards of CLO (97%), DFN (98%), DFZ (97%), and
standards of SA (99.5 %) were purchased from Aladdin Chemistry Co.,
Ltd. (Shanghai, China)
Reagents: Sodium chloride (NaCl) and anhydrous magnesium sulfate
(MgSO4) were purchased from Sinopharm Chemical Reagent
(Beijing, China). PSA (40-63 µm) was obtained from Tianjin Bonna-Agela
Technology Co., Ltd. (Tianjin, China). Acetonitrile (HPLC grade) was
obtained from Fisher Chemicals (Fair Lawn, NJ, USA).
2.2. Experiment
design
Plant cultivation: The seeds of cucumber were provided by the
Xintai Yuyuan Seed Industry Co., Ltd (Shandong, China). Cucumber seeds
were wrapped in wet gauze and placed in a petri dish to accelerate
germination. When the seeds germinating, we transferred the seeds into a
seedling tray and put one seed into each hole. The temperature of the
greenhouse was 25 ℃ in the day and 20 ℃ at night. After growth 21 days,
the young plants were used in pesticides exposure trials.
2.2.1. Pesticide
exposure experiments-uptake and translocation
Hydroponic experiments:The concentration of three pesticides was set at 5 mg
L-1, and the concentrations of SA were set at 1 mg
L-1,10 mg L-1, and 50 mg
L-1, respectively. CLO, DFN or DFZ was first dissolved
in acetonitrile to form the stock standard solution, respectively. And
then the standard stock solutions were diluted to the required
concentration by ultrapure water. SA was dissolved and diluted with 20
% methanol-water.
After germination, the cucumber seedlings were removed from the seedling
tray, and the roots were washed by deionized water before transferred to
hydroponic
cultivation buckets with 0.25 L modified Hoagland nutrient solution in
the greenhouse. The composition of the nutrient solution can be found inTable S2 . The growth conditions were the same as the plant
cultivation conditions. And a total of 12 treatments were set in the
experiment with 27 cucumber seedlings per treatment, the processing
information for each test can be found in Table 1 . The
hydroponic cultivation buckets were covered with aluminum foil to
prevent algae growth and water evaporation. The nutrient solution was
supplemented to the initial volume at 11 am every day.
Control experiments: Two control groups were included: nutrient
solution with cucumber seedlings without pesticides was as the treatment
of C1 group; and nutrient solution with CLO, DFN and DFZ but without
cucumber seedlings were as the treatments of CLO-C2, DFN-C2 and DFZ-C2
groups, respectively.
Sample collection: Cucumber seedlings were grown for 28
days, nutrient solution and plant
samples were collected at 0.25, 1, 3, 5, 7, 10, 14, 21, 28 days after
the transfer. The plants were divided into roots, stems and leaves for
pesticide analysis. At each sampling time, three replicate samples were
randomly taken. All samples were stored at -20℃ until analysis.