Effects of copper treatment on the redox state and secondary metabolism of Scutellaria baicalensis Georgi roots

Copper treatment can lead to the accumulation of reactive oxygen species, alter the cellular redox state in plants, and trigger plant adaptive mechanisms such as changes in gene expression and shifts in secondary metabolism. We investigated the effects of copper treatment on the redox state of Scutellaria baicalensis Georgi, characterized by glutathione (GSH) and oxidized glutathione (GSSG) levels. We also determined the concentrations of baicalin and baicalein, and analyzed the correlation between the redox state and these metabolites. Moreover, we analyzed the activity of glutathione reductase (GR, EC 1.6.4.2) and the expression levels of GR, phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and isochorismate synthase (ICS, EC 5.4.4.2) genes. Results indicated that copper treatment increased GSH concentration at 24 and 48 h, and the ratio of GSH:GSSG, and upregulated GR expression. While the baicalin concentration showed a non-significant increase at 24 h and 72 h, baicalein exhibited a significant decrease at 48 h and 72 h. The two key genes in the salicylic acid pathway, PAL and ICS, exhibited opposite trends at 24 and 48 h after copper treatment, followed by significant decreases in both PAL and ICS at 72 h. Our results suggest that plants can mitigate the toxic effects of copper through increasing GSH biosynthesis. Baicalin and baicalein showed varying accumulation patterns in S. baicalensis subjected to different copper treatments.