Ellagitannins have Greater Oxidative Activities than Condensed Tannins and Galloyl Glucoses at High pH: Potential Impact on Caterpillars

Abstract

Plants synthesize a diversity of tannin structures but little is known about whether these different types have different oxidative activities in herbivores. Oxidative activities of hydrolyzable and condensed tannins were compared at pH 10 with two methods: EPR spectrometry was used to quantify semiquinone radicals in anoxic conditions and a spectrophotometric assay was used to measure the rate of browning of phenolics oxidized in ambient oxygen conditions. A little-studied group of hydrolyzable tannins (ellagitannins) contained the most active tannins examined, forming high concentrations of semiquinone radicals and browning at the highest rates. On average, galloyl glucoses and high-molecular-weight gallotannins had intermediate to low oxidative activities. Condensed tannins generally formed low levels of semiquinone radicals and browned most slowly. The results suggest that ellagitannin-rich plants have active oxidative defenses against herbivores, such as caterpillars, whereas the opposite may hold true for plants that contain predominantly condensed tannins or high-molecular-weight gallotannins.

ent-Eudesmane sesquiterpenoids, galloyl esters of the oak lactone precursor, and a 3-O-methylellagic acid glycoside from the wood of Platycarya strobilacea

“…Another remarkable difference observed in the chromatograms is the significant decrease of ellagitannins pedunculagin (8), 1(β)-O-galloyl pedunculagin (9), casuariin (10) and casuarinin (11). This phenomenon is probably because ellagitannins are more sensitive to radical oxidation (Barbehenn et al, 2006). The products produced from ellagitannins remain unknown.…”

Gut pH, redox conditions and oxygen levels in an aquatic caterpillar: Potential effects on the fate of ingested tannins

“…The alkaline conditions prevalent in guts of lepidopteran larvae should promote ROS formation and result in deleterious effects. Among various tannins, ellagitannins have the highest oxidative activities and form the highest concentrations of semiquinone radicals (Barbehenn et al, 2006). It is possible that TII and other, not yet identified ellagitannins in M. spicatum might cause oxidative stress in A. ephemerella guts, resulting in the poorer performance when fed this plant .…”

“…Oxidation of polyphenols in the presence of oxygen generates reactive oxygen species (ROS; Barbehenn et al, 2006), which are harmful to cell membranes. In some polyphenol-sensitive lepidopteran species, ingestion of polyphenols leads to lesions in the gut epithelium (Steinly and Berenbaum, 1985;Lindroth and Peterson, 1988), and even tannin-tolerant species show elevated levels of oxidative damage of lipids in midgut tissues (Summers and Felton, 1994;Bi and Felton, 1995).…”

Immunological Memory of Mountain Birches: Effects of Phenolics on Performance of the Autumnal Moth Depend on Herbivory History of Trees

“…However, at high pH (e.g. in the midgut of caterpillars), some phenolics, such as ellagitannins, auto-oxidize into quinones that are highly reactive and also toxic compounds (Barbehenn et al 2006). Quinones form covalent bonds with nucleophilic moieties of biomolecules, such as the functional groups of amino acids and proteins, making them indigestible (Felton et al 1989).…”