Abstract :
[en] Pesticide application is essential for managing pests in medicinal plants, yet it inevitably introduces risks of pesticide residue accumulation, plant growth inhibition, and changes in the biosynthesis of bioactive compounds. Understanding the responses of medicinal plants to pesticide stress and developing effective approaches for reducing pesticide toxicity are important for the safe production of medicinal materials. Using Astragalus membranaceus as a model medicinal plant, this dissertation systematically investigates the uptake, translocation, metabolism, and phytotoxicity of three representative pesticides, including tebuconazole (TEB), atrazine (ATZ), and avermectin (AVM). In addition, two approaches for alleviating pesticide stress and reducing residues, namely endogenous hormone regulation and rhizosphere microbial remediation, were further evaluated.
All pesticides exhibited distinct patterns of uptake and distribution in A. membranaceus. ATZ was readily transported to the shoots, whereas TEB mainly accumulated in the roots and AVM showed very limited transport within the plant. These differences were closely associated with the physicochemical properties of the pesticides. All of them inhibited plant growth and caused membrane damage, but induced different physiological responses. TEB mainly affected phenylpropanoid metabolism and increased the expression of several genes associated with lignin biosynthesis, AVM induced changes in detoxification enzyme activities and peroxidase activity, whereas ATZ mainly affected flavonoid metabolism and energy related pathways. In addition, pesticide exposure altered the accumulation of triterpenoid saponins, and different biosynthetic branches responded differently to the three pesticides. Although the physiological responses varied among pesticides, all three treatments disturbed cytokinin homeostasis and inhibited root growth. Increased IPT expression, decreased CKX expression, and changes in cytokinin profiles were observed across the treatments, suggesting an association between altered cytokinin metabolism and root growth inhibition.
TEB was selected as a representative pesticide for subsequent intervention experiments. Exogenous methyl jasmonate (MeJA) partially restored plant growth, altered responses associated with Phase I and Phase II detoxification, and partially restored the accumulation of some bioactive compounds under TEB stress. Root TEB residues decreased by 6.23%. In contrast, DIECA treatment was associated with greater TEB accumulation, and reduced accumulation of some saponins, providing pharmacological evidence for the involvement of jasmonates in the response to TEB stress. Meanwhile, TEB changed the composition of root exudates and affected both endophytic and rhizosphere microbial communities. A bacterium capable of degrading TEB, Sphingobium yanoikuyae IPPH-98, was isolated from the rhizosphere of A. membranaceus. This strain showed chemotactic responses to selected compounds detected in root exudates and degraded TEB in culture. Inoculation with IPPH-98 reduced TEB residues in soil and plant roots, promoted plant growth, and increased root Soyasaponin I accumulation.
This study improves the current understanding of the physiological and molecular responses of medicinal plants to pesticide stress and provides a theoretical basis for pesticide residue control, quality maintenance, and the green production of medicinal plants.
