Polyphenolics in Rhizophora mangle L. leaves and their changes during leaf development and senescence

The chemical defenses in Rhizophora mangle L. are largely carbon based. The family has long been exploited for the high proanthocyanidin (condensed tannin) content of its wood, bark and leaves. In this paper, we quantify the overall pools of plant phenolics in R. mangle leaves, identify the major constituents of these pools and document their changes during leaf maturation and senescence. Overall, polyphenolics account for approximately 23% of the total leaf dry weight. The leaves contain at least seven flavonoid glycosides, five of them based on quercetin. Additional minor constituents are myricetin and kaempferol diglucosides. The aglycone, quercetin, was found only in senescing leaves. Also during senescence, a new compound, 5,4-dimethoxy-7,3,5-trihydroxyflavone, appeared. The flavonoids were accompanied by a complex mixture of condensed tannins based mainly on (+)-catechin and (–)-epicatechin with A-type and B-type linkages; this pool is also distinguished by having previously unreported, high contributions of (+)-catechin and (–)-epicatechin glycosides. During senescence, but prior to leaf abscission, the polyphenolic pools become simplified: flavonol glycosides and low oligomeric tannins largely disappear, leaving only the largest tannin polymers. The ecological and physiological significance of these compounds as they appear in R. mangle is discussed.