Activity of SDH, QDH, and PAL in species, accumulating different types of tannins

The biosynthesis of different classes of tannins in plants is a complex process that remains insufficiently studied. This study aimed to evaluate the activity of shikimate dehydrogenase (SDH), quinate dehydrogenase (QDH), and phenylalanine ammonia-lyase (PAL), and their influence on the accumulation of proanthocyanidins (PA) and/or hydrolyzable tannins (HT) in medicinal plants. The leaves of Hippophae rhamnoides and Cornus sericea (accumulating HT), Astilbe chinensis (accumulating PA), and Agrimonia pilosa and Agrimonia asiatica (accumulating both HT and PA) were used in the present study. The highest PA levels were found in A. chinensis, whereas the highest HT content was observed in H. rhamnoides. Water-soluble PA predominated in all species. The highest SDH activities were detected in the leaves of the HT-rich species C. sericea and H. rhamnoides, whereas QDH activity was comparatively low. The activity of PAL was the highest in the leaves of H. rhamnoides, and the lowest in A. chinensis. Correlation analysis revealed positive relationships between SDH and PAL activity and HT levels, and a negative relationship with PA levels. No significant correlation was found between QDH activity and tannin content. SDH activity positively correlated with the content of gallic acid and β-glucogallin, and negatively with catechin. No correlation was observed between PAL activity and the levels of catechin or epicatechin. Hierarchical clustering separated variables into two major groups: catechin, epicatechin, different fractions of PA, and QDH in one cluster, and SDH, PAL, HT, gallic acid, β-glucogallin, ellagic acid, pentagalloyl glucose, and chlorogenic acid in the other. Clustering by species revealed an HT-dominant group (H. rhamnoides and C. sericea) and a PA-dominant group (A. chinensis and Agrimonia spp.). These findings add valuable information to the enzymatic regulation of tannin biosynthesis in medicinal plants that accumulate different types of tannins.