The Chemistry and Chemical Ecology of Ellagitannins in Plant–Insect Interactions: From Underestimated Molecules to Bioactive Plant Constituents

Abstract

This chapter reviews our current knowledge of the chemistry and chemical ecology of ellagitannins (ETs), placing particular emphasis on the role these under-appreciated polyphenols play in plant-herbivore interactions. Instead of the traditional tannin-linked activity that comes from their complex formation with proteins, it discusses tannins' less well-known pro-oxidant activity. ETs are likely the most active tannin pro-oxidants. Plant cells synthesize ETs via the shikimate pathway, utilizing the enzymatic conversion of dehydroshikimic acid into gallic acid and further to galloyl glucoses. During the biosynthetic steps from monogalloyl glucose towards pentagalloyl glucose, the pro-oxidant activity of the polyphenols decreases, but it begins to increase again as soon as pentagalloyl glucose is transformed to glucopyranose-based ETs and further to very active C-glycosidic ETs. Thus, the tannin-based pro-oxidant capacity of a plant cell is highly dependent on the total and relative concentrations of different types of products or intermediates of the hydrolyzable tannin pathway. Within plant species that accumulate different types of galloyl glucoses and ETs differing in pro-oxidant activities, this balance typically varies significantly. The situation is further complicated by the variation in ETs observed seasonally and between individual plants. In addition, ETs may also derive their antiherbivore activities via their hydrolysis products, which is largely an unexplored area of research. Historically, ETs have not been taken specifically into account as plant-defense compounds, mainly due to difficulties in their compound-specific analysis from the plant cell. Recent developments in tannin chemistry have diminished these problems and the joint effort of ecologists and

Can genetically based clines in plant defence explain greater herbivory at higher latitudes?

“…; Salminen & Karonen ). Ellagitannins may also be oxidised before entering the gut by plant polyphenol oxidases and peroxidases, or they may bind and precipitate dietary proteins in the non‐alkaline pregut region (Salminen ). Past research has shown that there is genetic variation in the concentrations of most ellagitannins both within and between species (Johnson et al .…”

“…Ellagitannins are a group of hydrolysable tannins that are reactive within the alkaline conditions of insect guts, where they are thought to cause oxidative stress (Barbehenn et al 2006;. Ellagitannins may also be oxidised before entering the gut by plant polyphenol oxidases and peroxidases, or they may bind and precipitate dietary proteins in the non-alkaline pregut region (Salminen 2014). Past research has shown that there is genetic variation in the concentrations of most ellagitannins both within and between species (Johnson et al 2009;Johnson et al 2014).…”

Yellow, red, dead: the nutritional consequences for Cardiaspina densitexta (Hemiptera: Aphalaridae) nymphs of inducing senescence in old Eucalyptus fasciculosa leaves

“…the result that ETs and CTs do not accumulate simultaneously in high concentrations in the same tissues. In birch and oak leaves, ETs are expressed in higher concentrations in young tissues whereas CTs are expressed in higher concentrations in old tissues (Salminen 2014). Correspondingly, the pro-oxidant activity of foliar polyphenols declines with increasing age of plant tissues.…”

Two-Dimensional Tannin Fingerprints by Liquid Chromatography Tandem Mass Spectrometry Offer a New Dimension to Plant Tannin Analyses and Help To Visualize the Tannin Diversity in Plants

“…This 20 mg approach allows for the use of the same sample for many other purposes as well, such as sensitive bioactivity analyses and high-resolution mass spectrometry, if needed. 8 …”

“… 3 , 7 Simple gallic acid derivatives or gallotannins rarely produce oligomers because they are typically found as monomers only. 8 In practice, these tannins can be quantified individually all of the way to the heptamers, 9 although even undecamers have been found in plants. 10 The third general group of tannins is the phlorotannins (consisting of two or more phloroglusinol units), but because they are mainly found in marine organisms, such as brown algae, they are not dealt with here (but see the study by Salminen and Karonen 3 for details).…”