4.4. Mechanisms of alleviates phytotoxicity by exogenous SA
In our study, three concentrations
of exogenous SA were supplemented to assess the effects of SA on
pesticides-induced oxidative stress in cucumber plants. Based on the
above results, we found that low concentration of SA (1mg
L-1 and 10mg L-1) had significant
effects on relieving oxidative stress of cucumber plants induced by the
three pesticides. Whereas, high concentration of exogenous SA (50 mg
L-1) had little effect on alleviating oxidative stress
of cucumber plants. Therefore, the effects of exogenous SA on reducing
oxidative stress depends on its concentrations. In accordance with the
present results, previous studies have demonstrated that low
concentration of SA can improve the tolerance of plants to adversity. In
contrast, high concentration of SA induced a higher level of oxidative
stress, leading to a decrease in tolerance to environmental stress (Bai,
Dong, Kong, Xu, & Liu, 2014; Z. Liu, Ding, Wang, Ye, & Zhu, 2016;
Pasternak et al., 2019). In the previous part of this study, we found
that exogenous SA could impair the absorption capacity of roots to
pesticides and thus reduce the accumulation of pesticides in cucumber
plants. These results matched those observed in earlier studies. SA
could reduce the accumulation of
chlorpyrifos in wheat plants by
decreasing uptake and translocation abilities of chlorpyrifos (C. Wang
& Zhang, 2017). SA could reduce the accumulation of isoproturon in
wheat by promoting its degradation (L. Liang et al., 2012; Yi Chen Lu et
al., 2014). SA could reduce the residual of flurochloridone in sunflower
leaves by the foliar treatment (Kaya & Yigit, 2014).
SA
was able to reduce the
concentration of thiamethoxam, hymexazol and chlorantraniliprole in
roots and leaves of cucumber plants and the uptake ability of roots, the
bioconcentration ability of plants, and the translocation ability from
roots to leaves were weakened (T. Liu et al., 2020). Taken together, we
speculated that SA mitigated phytotoxicity by weakening the uptake
ability of pesticides in plants and enhancing the capacity of
antioxidative stress. However, the exact mechanism of SA on plant stress
resistance needs to be further illuminated.