Metabolism of Phenylpropanoid Compounds in Apple Fruit Cell Suspension Culture

Abstract

A cell suspension culture, derived from apple ( Pyrus malus ) fruit parenchyma, was found to accumulate a number of hydroxycinnamoyl esters which were identified, in decreasing order, as chlorogenic acid, feruloyl quinic acid, sinapoyl glucose, feruloyl glucose and p -coumaroyl glucose. During aging of the culture, there was a significant increase in the accumulation of feruloyl and sinapoyl derivatives which was concomitant with a decrease in the chlorogenic acid content. The quantitative pattern of phenolic accumulation exhibited a gradual decline during the lag and early-exponential phases of culture growth, followed by a sharp increase in mid-and late-exponential growth, indicating intensive phenolic synthesis during active cell division. The activity of the enzymes of phenylpropanoid metabolism: phenylalanine ammonia-lyase. cinnamate-4-hydroxylase, O-methyltransferase and glucosyltransferase was studied during growth of the culture. The activity changes of these enzymes indicate a high degree of sequential coordination in regulating phenolic synthesis and its accumulation. Two peaks of activity for C-4-H were evident; one coincided with the high activity of PAL and the other was associated with OMT activity. The O-methylation of chlorogenic acid, albeit its low methyl acceptor ability, suggests a possible route for the biosynthesis of feruloyl quinic acid which is an important constituent of the cell culture. The pattern of GT activity, in relation to the other phenylpropanoid enzymes, indicates that glucosylation is a terminal step in the biosynthesis of phenolic compounds.