New approaches to tannin analysis of leaves can be used to explain in vitro biological activities associated with herbivore defence.

Karen J. Marsh,Carsten Kulheim,William J. Foley,Ian R. Wallis,Robert Clark,Dean Nicolle,Juha‐Pekka Salminen

doi:10.1111/nph.16117

Karen J. Marsh, Carsten Kulheim + Show 5 more

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https://doi.org/10.1111/nph.16117

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Abstract

Summary Although tannins have been an important focus of studies of plant–animal interactions, traditional tannin analyses cannot differentiate between the diversity of structures present in plants. This has limited our understanding of how different mixtures of these widespread secondary metabolites contribute to variation in biological activity.We used UPLC‐MS/MS to determine the concentration and broad composition of tannins and polyphenols in 628 eucalypt (Eucalyptus, Corymbia and Angophora) samples, and related these to three in vitro functional measures believed to influence herbivore defence: protein precipitation capacity, oxidative activity at high pH and capacity to reduce in vitro nitrogen (N) digestibility.Protein precipitation capacity was most strongly correlated with concentrations of procyanidin subunits in proanthocyanidins (PAs), and late‐eluting ellagitannins. Capacity to reduce in vitro N digestibility was affected most by the subunit composition and mean degree of polymerisation (mDP) of PAs. Finally, concentrations of ellagitannins and prodelphinidin subunits of PAs were the strongest determinants of oxidative activity.The results illustrate why measures of total tannins rarely correlate with animal feeding responses. However, they also confirm that the analytical techniques utilised here could allow researchers to understand how variation in tannins influence the ecology of individuals and populations of herbivores, and, ultimately, other ecosystem processes.

Highlights

Biologists often assume that a primary role of tannins is to defend plants against herbivory
We found wide variation in the protein precipitation capacity (0–229 mg gÀ1 dry matter (DM) pentagalloyl glucose equivalents), oxidative activity (2–94 mg gÀ1 DM gallic acid equivalents, or 3–79% of total phenolics) and capacity to reduce in vitro N digestibility (0–89 percentage units) between eucalypt species (Table 2)
Our study shows that the tannin composition of plant extracts affects their biological activity

Summary

Introduction

Biologists often assume that a primary role of tannins is to defend plants against herbivory. There are, thousands of tannin compounds displaying a diverse array of structures that often occur in complex mixtures of tens to hundreds of compounds These structures influence the response to standard colorimetric assays (Schofield et al, 2001), but they affect the biological activity of tannins, including their ability to bind proteins (Porter & Woodruffe, 1984; Jones & Palmer, 2000; Karonen et al, 2015), their pro- or antioxidant capacities (Barbehenn et al, 2006; Moilanen & Salminen, 2008; Moilanen et al, 2016), and, their effects on herbivores (Ayres et al, 1997; Makkar, 2003; Mueller-Harvey, 2006; Roslin & Salminen, 2008). Some ecologists have circumvented this problem by relating measures of herbivory to functional attributes of tannins, such as their capacity to precipitate protein (Robbins et al, 1987; e.g. McArt et al, 2009), reduce nitrogen (N) digestibility (e.g. DeGabriel et al, 2009; McArt et al, 2009) or oxidise at high pH (e.g. Appel, 1993; Steinbauer et al, 2016; Marsh et al, 2017b)

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