2.3. Determination of CLO, DFN and DFZ in cucumber plants
For “pesticide exposure experiments- uptake and
translocation” part, the contents of pesticides in plant tissue
samples were analyzed. The QuECHERS method was used to prepare nutrient
solution and plant tissue samples (Ge et al., 2017). The specific sample
preparation steps and instrumental analysis conditions are shown in
the supplementary materials .
The
recoveries of three pesticides in nutrient solution and plant tissues
were used to verify the feasibility of the analytical method. External
standard method was used for quantitative analysis. The results of
quality assurance and quality control are shown in
the supplementary
materials .
2.4.Determination
of antioxidant enzyme activity
The extraction of enzyme liquid was carried out according to the method
described by Andrews et al. (2005).
The method of SOD determination
referred to Farouk and Al-Amri (2019). APX activity was determined by
the reduction value of absorbance at 290 nm per unit time using the
method of Kaya and Doganlar (2016). GST activity was tested according to
Habig, Pabst, and Jakoby (1974).
The specific measurement steps are
shown in the supplementary materials .
2.5. Determination of the
total chlorophyll andH2O2content in cucumber plants
The pigment was extracted by methanol extraction following the method of
L. Zhao et al. (2019). The specific measurement steps are shown in thesupplementary materials . The content of
H2O2 in cucumber roots was determined by
H2O2 kits.
2.6. Determination of the
malondialdehyde (MDA) content
The level of lipid peroxidation was evaluated by the determination of
malondialdehyde (MDA) content based on the method of Heath and Packer
(1968). The specific measurement steps are shown in thesupplementary materials .
2.7. Determination ofproline content
The content of proline in plant roots was determined according to the
method of Bates, Waldren, and Teare
(1973). The specific measurement
steps are shown in the supplementary materials .
2.8. Data processing and
statistical analysis
In order to compare the difference in the behaviors of three pesticides
between supplementing different concentrations of SA and without SA, the
root concentration factor (RCF) and translocation factor (TF) were
calculated. The root concentration factor (RCF) was used to indicate the
ability to absorb target compounds by plant roots in nutrient solution,
RCF > 1 indicates that the compound is easily absorbed by
the roots, and calculated as follows (Qiu et al., 2016): (Eqn 1)
\(\mathrm{RCF=}\frac{\mathrm{concentration\ in\ root\ (mg/kg)}}{\mathrm{concentration\ in\ nutrient\ solution\ (mg/L)}}\)
Translocation factors (TF) was used to indicate the ability of leaves
and stems to transport target compounds from roots, TF>1
indicates that the excellent capacity for stems and leaves to
translocate the pesticides from roots, and calculated as follows (Ge et
al., 2016): (Eqn 2 and Eqn 3)
\(\ \mathrm{\text{TF}}\mathrm{\text{stem}}=\frac{\mathrm{concentration\ in\ stem\ (mg/kg)}}{\mathrm{concentration\ in\ root\ (mg/kg)}}\)
\(\ \mathrm{\text{TF}}\mathrm{\text{leaf}}\mathrm{\ }=\frac{\mathrm{concentration\ in\ leaf\ (mg/kg)\ }}{\mathrm{concentration\ in\ root\ (mg/kg)}}\)
The concentration of pesticides in nutrient solution was calculated
using the first-order equation
Ct=C0e-kt. The
half-life was calculated by the equation t1/2 =ln2/k,
where Ct is the concentration of target pesticides at
time t (days), C0 is the concentration of target
pesticides at the initial time, and k is the first-order rate constant
(day -1).
An independent sample t-test was used to compare the differences between
different treatments and pesticides. All statistical analyses were
statistical significance at the 0.05 level.