Metabotype Concept: Flexibility, Usefulness and Meaning in Different Biological Populations

Abstract

Analysis of plant diversity aims to understand the organization and the variability of biological populations within ecosystems. In classical analysis, individual plants are firstly identified on the basis of morphological/cytological parameters, then biodiversity is evaluated tacking into account presence/absence, abundances and densities of plants. Although morphological parameters are easily accessible, they provide limited precision on the differentiation between individuals that share a high similarity. This is especially true in the plant world where a same species includes several varieties that could not be easily distinguished morphologically. Cytological parameters provide reliable qualitative information but are not suitable for a quantitative evaluation of biodiversity at ecosystemic scales. The high variability between and within plant taxa can be highlighted chemically through qualitative and quantitative analyses of secondary metabolite patterns in different plants. Quantitatively, the different patterns show variability based on occurrences of different metabolites which can have major or minor levels. In the case where two chemical patterns have the same metabolites, they can be distinguished from different relative levels (i.e. regulation ratios) of such metabolites. These different variability criteria (presence/absence, major/minor, relative levels) allow to extract reliable chemical fingerprints for chemotaxonomical classification of plants. Moreover, such chemical polymorphism can be correlated to different intrinsic and/or extrinsic conditions of the plants in order to evaluate its adaptative, selective and/or evolutive values. Finally, relationships between chemical patterns and environmental conditions provide efficient tools to survey qualitatively and quantitatively the fluctuations of plant diversity in time and space. This chapter provides a review on chemotaxonomical criteria helping to understand complex structures of plant diversity. It focuses particularly on the chemotaxonomic usefulness of phenolic compounds (phenylpropanoids, flavonoids, etc.) in analysis of chemical polymorphisms at different systematic levels (from family to variety and chemotype via genus and species). Five plant families are treated here consisting of Poaceae and Liliaceae (monocotyledons), and Asteraceae, Lamiaceae and Fabaceae (dicotyledons). These families are representative of a great biomass part in the grasslands, and their chemotaxonomic analyses can usefully help to manage the biodiversity in such ecosystems.