DISTRIBUTION AND TURNOVER RATE OF SOLUBLE AND INSOLUBLE CAFFEOYL ESTERS IN XANTHIUM

Chlorogenic acid labelled in the caffeoyl moiety from trans-(U-14C)cinnamic acid has a half-life of 9 hr in young leaves, 24 hr in mature leaves, 19 hr in young stem sections and 14 hr in roots of Xanthium. As label is lost from chlorogenic acid, activity appears largely in 3,5-dicaffeoylquinic acid and insoluble residues. The rate of gain or loss of activity of these fractions differs in the various tissues, but some generalities can be made. During the 2 hr immediately following tracer application (applied for 1 hr) most of the label appears in insoluble residues. In a subsequent 20 hr period there is a slower though continued incorporation into this fraction in young leaves and roots. The rate of loss of activity from chlorogenic acid during the 2-22 hr after application of the tracer suggests a first order reaction of utilization. Most of the label appears in 3,5-dicaffeoylquinic acid during this time. From a consideration of these results and others obtained by feeding caffeoyl or quinic labelled chlorogenic acid to Xanthium leaves, it appears that the enzymes for lignin synthesis may be in the cell wall. As chlorogenic acid enters the primary cell wall or passes through the plasmalemma, many of the caffeoyl and quinic moieties arising by de-esterification are utilized in the synthesis of insoluble polymers, presumably lignin. The remainder migrates into the cytoplasm where a predominant chlorogenic to 3,5-dicaffeoylquinic acid conversion is observed. Insoluble caffeoyl esters which occur in Xanthium, especially in the roots and young leaves, are labelled very slowly and appear to play no part in the interrelations discussed. © 1968.