VOC-Mediated Priming Under Copper Stress Alters Metabolite Composition in Scutellaria baicalensis and Neighbouring Seedlings.

Plants under stress emit volatile organic compounds (VOCs) that can influence neighbouring plants. While most studies have focused on the role of VOCs priming the fitness of neighbouring plants, their involvement in priming bioactive compound accumulation in herbal plants remains less clear. In this study, we treated Scutellaria baicalensis Georgi using copper solution, identified the VOCs emitted from S. baicalensis and VOCs accumulated internally in tissues, and quantified total flavonoid and major bioactive compounds. We found that copper treatment inhibited the emissions of acetic acid butyl ester, cyclopentanone and ethyl 2-methylpropanoate. Concurrently, it significantly increased internal levels of 2-propanone and 3-methyl-3-buten-1-ol in aerial parts of both copper-treated (COT) and cocultured untreated (COU) seedlings, alongside a marked decrease in ethanol in COT. In underground parts, the 2-ethyl-1-hexanol and methoxybenzene only presented in COT, the 1-hexanol, 2-acetylfuran and n-pentanal exhibited higher accumulation in both COT and COU. Moreover, copper also enhanced total flavonoid content in COT and, notably, in COU, indicating a priming effect. Individual flavonoids showed a nuanced fluctuation in the aerial parts, but a general decrease in the underground parts. Together, our findings indicate that copper-induced airborne cues, dominated by VOCs, prime neighbouring plants to reconfigure phytochemical profiles, with consequences for herbal quality via shifts in bioactive compound composition.