A spatially-resolved approach to visualize the distribution and biosynthesis of flavones in Scutellaria baicalensis Georgi.

Imaging the spatial distributions and dynamics of flavones in heterogeneous plant tissues is significant for our understanding of plant metabolism. Here, we proposed a spatially-resolved approach to map the locations and biosynthesis of flavones in S. baicalensis. A total of 11 flavones, 5 flavone glycosides, 6 carbohydrates, and a variety of flavone synthesis-related metabolites were imaged. Most of these flavone-related metabolites presented stronger ion intensities in root phloem. The biosynthetic network of flavones and their glycosides in S. baicalensis were visualized for the first time. Moreover, we characterized the region-specific activities of four crucial enzymes in flavone synthesis pathway, including l-phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, 4-coumarate coenzyme A ligase, and flavone synthase. In line with the spatial characteristic of flavones, all these four enzymes exhibit higher activity in the root phloem of S. baicalensis. The combination of spatially-resolved metabolites and enzymes information greatly broadens our understanding of flavone biosynthetic network.