Effects of competitive inhibitors of phenylalanine ammonia‐lyase on the levels of phenylpropanoid enzymes in Solatium tuberosum

Abstract

Abstract The accumulation of chlorogenic acid in illuminated discs of Solanum tuberosum tuber tissue is accompanied by rapid but transient increases in the activity levels of the biosynthetic enzymes phenylalanine ammonia‐lyase, cinnamic acid 4‐hydroxylase and hydroxycinnamoyl‐CoA : quinate hydroxycinna‐moyl transferase. Exogenous D‐phenylalanine and L‐α‐aminooxy‐β‐phenylpropionic acid, competitive inhibitors of phenylalanine ammonia‐lyase, inhibit the accumulation of chlorogenic acid and presumably reduce the endogenous pools of pathway intermediates such as cinnamic acid. These treatments prolong the phase of increase in phenylalanine ammonia‐lyase and cinnamic acid 4‐hydroxylase activities and indicate that product feedback modulation is important in maintaining the interrelationship between the levels of these two enzymes during the later stages of induction. In contrast,L‐α‐aminooxy‐β‐phenylpropionic acid inhibits the development of hydroxycinnamoyl transferase in illuminated discs supporting the idea that the light‐stimulated increase in phenylalanine ammonia‐lyase activity causes an increase in cinnamic acid production which mediates the light‐stimulated increase in hydroxycinnamoyl transferase activity.