Histochemical detection of an haematommoyl alcohol dehydrogenase in the lichen Evernia prunastri

Atranorin, one of the most abundant phenols of Evernia prunastri, is mainly located in the cortex together with evernic acid. Atranorin is produced by esterification of two different precursors, methyl β-orcinol carboxylate and haematommic acid. This last compound is produced from methyl-3-orsellinate by the successive action of an oxidase and an alcohol dehydrogenase. This alcohol dehydrogenase oxidizes haematommoyl alcohol to haematomic acid, and catalyzes the reduction of the aldehyde function in the atranorin molecule. Other analogs of haematommoyl alcohol, such as orcinol or methyl β-orcinol carboxylate, were not used as substrate by this alcohol dehydrogenase. The enzyme has been located in the medullary hyphae, especially in those immediately above the lower cortex. Thus, haematommoyl alcohol dehydrogenase activity seems to be restricted to the fungal partner in the lichen thallus. This enzyme is here described for the first time in lichens.