Temperature regimes mediate ROS metabolism and MAPK signaling to modulate flavonoid accumulation and quality in Scutellaria baicalensis roots

Extensively applied in traditional Chinese herbal medicine, Scutellaria baicalensis Georgi is a key botanical resource. The synthesis of its main active components, flavonoids, is significantly affected by temperature. In this study, two-year-old S. baicalensis were subjected to three temperature treatments: low temperature with high diurnal temperature variation (LH), low temperature with low diurnal temperature variation (LL), and high temperature with low diurnal temperature variation (HL). This study employed a multi-omics approach-integrating phenotypic, transcriptomic, and metabolomic analyses-combined with biochemical assays, qRT-PCR validation, and HPLC quantification to elucidate the impact of temperature regimes on growth traits, transcriptional regulation, metabolic biosynthesis, and the pharmaceutical quality of S. baicalensis. The results demonstrated distinctive responses across treatments: while the HL treatment extended the root system at the cost of aboveground biomass, comparative analysis revealed that the LH treatment significantly promoted stem development compared to the LL group. Transcriptomic analysis indicated that HL conditions upregulated MAPK signaling pathway-associated genes to enhance stress resistance, whereas gene expression patterns related to flavonoid biosynthesis were most active under LH conditions. Metabolomics showed that under HL conditions, the accumulation of key flavonoid glycosides such as baicalin was reduced due to hindered glycosylation, while LH maintained superior levels of these active compounds relative to LL and HL. Additionally, HL conditions triggered reactive oxygen species (ROS) accumulation and increased malondialdehyde (MDA) content, prompting a shift in antioxidant enzyme activities and the accumulation of osmotic adjustment compounds as an adaptation strategy. These findings reveal the critical role of temperature dynamics in quality formation. Specifically, low temperature coupled with high diurnal variation (LH) was identified as the optimal condition for balancing growth and high-quality flavonoid accumulation. This study establishes a theoretical foundation for leveraging diurnal temperature differences to achieve both superior quality and high yield in the cultivation of S. baicalensis.