Evidence for Covalently Attached p-Coumaric Acid and Ferulic Acid in Cutins and Suberins

Abstract

p-Coumaric acid (4-hydroxycinnamic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) have been identified as constituents of cutin. Their reduction products were isolated from a phenolic fraction released from the cutin of the fruits of apple, peach, pear, and two varieties of tomato and apple leaf by treatment with LiAlH₄ or LiAlD₄. They were identified by combined gas chromatography and mass spectrometry. p-Coumaric acid was present in all samples of cutin (0.07-0.53% by weight), whereas only peach and pear cutin contained measurable amounts of ferulic acid (0.007% and 0.035%, respectively). Both p-coumaric acid and ferulic acid were identified to be constituents of the insoluble material recovered after partial hydrolysis (12-42% loss) of cutin in 1 m NaOH at 80 C. A significant part (48%) of the p-coumaric acid contained in tomato cutin was contained in the insoluble material recovered after partial degradation (7.4%) of this cutin with 0.01 m NaOH. These data indicate that these phenolic components are tightly (possibly covalently) bound to cutin. Similar analysis of the phenolic fractions from the suberins of potato, sweet potato, turnip, rutabaga, carrot, and red beet revealed that they contained only ferulic acid (0.05-0.22%). Ferulic acid was identified as a constituent of the insoluble material recovered after partial hydrolysis of potato and beet suberins (34% and 32% loss, respectively) in 1 m NaOH at 80 C. A major part (65%) of the ferulic acid contained in potato suberin was contained in the insoluble material recovered after partial (26.8% loss) degradation of this suberin with 0.01 m NaOH. Ferulic acid appears to be tightly (probably covalently) bound to suberin.