This study investigates the novel application of silicon nanoparticles (SiO₂ NPs) to enhance drought tolerance and medicinal quality in the threatened medicinal plant Sophora tonkinensis, providing technical support for its conservation and cultivation. Six treatments were applied: control (CK), CK + 100 mg/L SiO₂ NPs, CK + 200 mg/L SiO₂ NPs, drought stress (SD), SD + 100 mg/L SiO₂ NPs, SD + 200 mg/L SiO₂ NPs. After 21 days of foliar application, we assessed biomass, physio–biochemical parameters (including soluble protein, soluble sugar, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), malondialdehyde (MDA), superoxide anion (O₂⁻), and hydrogen peroxide (H₂O₂)), as well as concentrations of matrine, oxymatrine, genistin, genistein, total alkaloids, and total flavonoids. Under drought stress, the application of 100 mg/L SiO₂ NPs was the most effective treatment for enhancing biomass accumulation and eliciting a coordinated physio–biochemical response. This was demonstrated by a significant increase in leaf soluble protein content and root SOD activity, along with a decrease in oxidative stress markers (H₂O₂ and O₂⁻). Furthermore, SiO₂ NPs application under both normal and drought conditions selectively enhanced the accumulation of bioactive compounds in the roots, with the optimal concentration being compound-specific. Notably, under drought conditions, the application of 200 mg/L SiO₂ NPs proved optimal for enhancing the biosynthesis of several key medicinal compounds in the roots. Specifically, this treatment significantly maximized the content of matrine (214.15 μg/g), genistin (4.06 μg/g), genistein (48.56 μg/g), total alkaloids (9.96 mg/g), and total flavonoids (11.44 mg/g) compared to the drought-stressed control (SD). These results demonstrate that SiO₂ NPs significantly improve yield and key medicinal components of S. tonkinensis under drought stress, with a differential efficiency depending on the concentration, plant organ, and target compound.

Spatholobus suberectus Dunn is rich in flavonoids, which were previously demonstrated to respond to changing light conditions. In this study, through weighted gene co-expression network analysis (WGCNA), MYB genes were screened as the potential regulator for these light-intensity-induced changes. One MYB gene, SsMYB106, was chosen for in-depth research. Analysis showed that SsMYB106 was an R2R3-type MYB transcription factor, regulated by light, and involved in controlling the light responses of S. suberectus. SsMYB106 was then transiently overexpressed in S. suberectus flowers and stably overexpressed in Nicotiana benthamiana Domin. SsMYB106 overexpression promoted flavonoids (especially catechins) accumulation, and affected expressions of all the flavonoid biosynthetic pathway genes. In transient overexpression, SsDFR1 was the only significantly decreased gene, while other 17 genes were significantly increased. In stable overexpression, nearly all genes were upregulated or at least unchanged. SsMYB106 overexpression also might function in inhibiting anthocyanin and lignin biosynthesis. This study deepens our understanding of SsMYBs gene functions in regulating and enhancing flavonoids, and would be beneficial for designing high-valued S. suberectus in future.

The medicinal plant Spatholobus suberectus Dunn is easily exposed to shade stress during growth, but its shade responses and shade stress resistant mechanisms have not been clarified. In this study, shade treatments including four attenuated sunlight intensities (100%, 60%, 40%, and 10%) and three shade durations (30 d, 45 d, and 60 d) were applied to S. suberectus. The shade-induced morphological indicators, phytohormonal regulations, metabolic flavonoids contents, transcriptomic flavonoid pathway gene expressions, and stress physiological changes of S. suberectus were analyzed. The putative promoter cis-regulatory elements (CREs) of 18 flavonoid biosynthetic pathway genes were identified. Results showed the stem growth indicators of S. suberectus were better at 40% light intensity. Phytohormones were involved in the shade-induced responses. Short-term shade (30 d) increased total flavonoids, gallated catechins and especially epigallocatechin gallate contents and favored for boosting medicinal value. Long-term shade (45 d, 60 d) tended to decrease flavonoids. The shade-induced flavonoids changes were attributed to their corresponding biosynthesizing genes expression variations. The high antioxidant capacity and the presence of phytohormone-, stress-, and development-related CREs provided the basis for stress resistance. In conclusion, the multiple responses under shade and the CREs analysis elucidated S. suberectus’ shade tolerance.