ABSTRACT:
Salicylic acid (SA) is an important signal molecule, regulating
oxidative stress response in plants. In this study, we evaluated the
influences of SA (1mg L-1, 10mg L-1and 50mg L-1) on the accumulation of clothianidin
(CLO), dinotefuran (DFN) and difenoconazole (DFZ) (5mg
L-1) and pesticide-induced (CLO-10mg
L-1, DFN-20 mg L-1, and DFZ-10mg
L-1) oxidative stress in cucumber plants. Exogenous SA
at 10mg L-1 significantly reduced the half-lives of
three pesticides in nutrient solution and prevented the accumulation of
pesticides in roots and leaves. And the role of SA in reducing residues
was related to the major accumulation sites of pesticides. By
calculating the root concentration factor (RCF) and translocation factor
(TF), we found that SA at 10mg L-1 reduced the ability
of roots to absorb pesticides and enhanced the translocation ability
from roots to leaves. Roots exposed to high concentrations of three
pesticides could reduce biomass, low chlorophyll content, promote lipid
peroxidation, and alter the activities of a range of antioxidant
enzymes, respectively. Exogenous
SA at low concentrations significantly mitigated these negative effects.
Hence, we speculated that application of exogenous SA at 10 mg
L-1 could effectively alleviate the accumulation of
pesticides and induce stress tolerance in cucumber planting systems.
Keywords: Pesticides, Cucumber, Uptake, Translocation,
Salicylic acid, Oxidative stress
Introduction
As
a kind of plant protection product, pesticides play an important role in
controlling diseases, insects, weeds, and increasing yield of crops (J.
Liang & Tang, 2010). However, its misuse has caused a series of
environmental safety and food safety problems. For example, some
neonicotinoids have raised concerns about their toxicity to bees, which
put them at risk of being banned
(Jiang et al., 2018; Jiang, Zhang, Lin, Liu, & Mu, 2019). Moreover,
overuse of pesticides may cause pesticide pollution in agricultural
products as well as soil and water (K. Wang, Wu, & Zhang, 2012). And
once the excessive accumulation of pesticides will cause phytotoxicity
by injuring the physiological structure of plants (Mahapatra, De,
Banerjee, & Roy, 2019). Therefore, it is necessary to investigate the
uptake, translocation and accumulation behaviors of systemic pesticides
in plants and make effective strategies to reduce pesticide stress.
The
active expression of pesticides is closely related to its uptake and
translocation behaviors in plants. On the one hand, the uptake and
translocation behaviors of pesticides affect the efficacy and duration,
which is beneficial to choose the application technology of pesticides
(Huang et al., 2019); On the other hand, it is helpful to further
understand the dynamic distribution and accumulation of pesticides in
various parts of plants and clarify the dynamics residues of pesticides
in the environment (Hingmire, Oulkar, Utture, Ahammed Shabeer, &
Banerjee, 2015; Utture et al., 2011). Previous studies have reported
that the uptake and translocation behaviors of systemic pesticides in
plants are related to their physical and chemical properties, such as
octanol/water partition coefficient (logKow ), water
solubility and molecular weight (Y. Li, Long, et al., 2018; Namiki,
Otani, Motoki, Seike, & Iwafune, 2018; Qiu et al., 2016), but also are
related to the plant species, growth conditions, growth stage,
application method and other factors (Ge et al., 2016; Hwang, Lee, &
Kim, 2015; Y. Li, Yang, et al., 2018).
When
plants subjected to various biological and abiotic stresses, a large
number of reactive oxygen species (ROS) can accumulate in the cells,
which can destroy the cell molecular structure and interfere with the
physiological process of plants (Noctor, Mhamdi, & Foyer, 2016). For
defense, plants have a variety of complex enzymatic and non-enzymatic
antioxidant systems that they can resist oxidative stress including
superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate
peroxidase (APX) and other enzymes and non-enzymatic substances they can
remove different types ROS (Safari, Akramian, Salehi-Arjmand, &
Khadivi, 2019). As a result of human production activities, many wastes
remained in the environment for a long time, which can produce stress
responses to plants such as heavy metals, pesticides, and engineered
nanomaterials (Lian et al., 2020; Rodriguez-Serrano et al., 2006; Safari
et al., 2019). Salicylic acid (SA) is a well-known endogenous signaling
molecule related to plants stress resistance (Q. J. Wang et al., 2016;
X. Y. Zhao et al., 2020; X. Y. Zhao et al., 2019). When plants are in
adverse environments, SA can regulate various physiological and
biochemical processes of plants to alleviate stress (W. Y. Song, Peng,
Shao, Shao, & Yang, 2014; Q. Wang et al., 2013; Xu, Fan, Dong, Kong, &
Bai, 2014). It is worth noting that SA can inhibit the accumulation of
pesticides in plants, which is vital for reducing pesticide residues and
ensuring the safety of agricultural products (Kaya & Yigit, 2014; C.
Wang & Zhang, 2017). For phytotoxicity caused by pesticides, most
previous studies focused on exogenous SA to reduce the toxicity of
herbicides on nontarget plants (Akbulut, Yigit, Kaya, & Aktas, 2018;
Kaya & Doganlar, 2016). However,
the regulatory functions of SA under commonly used systemic pesticide
stress and the effects of exogenous SA on the accumulation of pesticides
in various parts of the plants were rarely investigated.
Cucumber(Cucumis sativus L. ) is a widely cultivated cash crop in
China. In the present study, the three pesticides, clothianidin (CLO),
dinotefuran (DFN) and difenoconazole (DFZ) were selected as the
representatives. CLO is a neonicotinoid insecticide with excellent
systemic and osmotic activity that can be used as a soil, spray and seed
treatment, for control of sucking and chewing insects (Jeschke, Nauen,
Schindler, & Elbert, 2011). DFN is a systemic neonicotinoid insecticide
with translaminar activity, and it can be applied on foliage, soil and
nursery boxes by spray, drench, broadcast and pricking-in-hole
treatments (Corbel, Duchon, Zaim, & Hougard, 2004). DFZ is a systemic
fungicide of sterol demethylation inhibitors with a novel broad-range
activity protecting the yield and crop quality by foliar application or
seed treatment (Dong et al., 2013). The three pesticides all could be
absorbed by plant roots, which can be used for soil treatment, but there
are significant differences in water solubility and
logKow of the three pesticides. The physical and
chemical properties of these three pesticides are shown in Table
S1 . We investigated the effects of exogenous SA on the uptake,
translocation and accumulation behaviors of these three pesticides in
cucumber plants by measuring the concentration of pesticides in various
parts of the cucumber plants and calculating the root concentration
factor (RCF) and translocation factor (TF) values. Moreover, the effects
of SA on oxidative stress induced by these three pesticides to the
cucumber plants were also studied by measuring biomass, photosynthetic
pigment content, antioxidants content and
antioxidant enzyme activities.
This study provides a new perspective to understand the uptake and
translocation behaviors of pesticides and pesticide pollution in plants.