Biosynthesis and subcellular distribution of hydrolyzable tannins.

Pathways to complex gallotannins have been elucidated by enzyme studies, indicating that beta-glucogallin is required as principal acyl donor. Evidence for the in vitro oxidation of pentagalloylglucose, the pivotal metabolite in this sequence, to ellagitannins, is presented. Immunohistochemical studies with antibodies raised against pentagalloylglucose and the galloyltransferase catalyzing the formation of this ester revealed that leaf mesophyll cell walls were a typical site of origin and deposition of hydrolyzable tannins. Seasonal changes of these compounds were studied with extracts from cell walls and intracellular space of oak leaves.