Higher plants are well known for the vast diversity of metabolites they produce. This diversity can be considered from two different angles. The first considers the diversity of metabolites between species, or groups of species. From this taxonomic point of view, metabolites can be classified as ubiquitous, i.e. present in all plant species, or restricted to certain species, genera, families, or larger taxonomic groups. Compounds which are present in all species such as primary metabolites and hormones play fundamental roles in plant growth and reproduction. Compounds with a more restricted distribution constitute the group of what is generally considered secondary metabolites, which are largely responsible for the metabolic diversity of plants. Their function is often more difficult to evaluate because they are likely to play specialized roles in the complex interaction of the species with its specific habitat and in the response to biotic or abiotic environmental challenges. The diversity of these metabolites has, however, raised considerable interest because of their potential use in various industrial areas, such as fragrance, flavor, pharmaceuticals, fine chemicals, and pesticides among others.
A second way of looking at metabolites and metabolic pathways is by considering their precise localization in the plant, whether at the organ, tissue, cellular or sub-cellular level. The information on the site of production, metabolic fluxes and the storage of the compounds is crucial to gain insight into the specific in vivo function and biological role of the metabolites, be they trace components, like hormones or highly abundant, like some secondary metabolites. It is with these two visions in mind that the Department of Cell and Metabolic Biology (CMB) aims at understanding the biosynthesis and function of plant metabolites, in particular hormones and secondary compounds, using several plant species, including model species like Arabidopsis thaliana, Medicago truncatula, but also tomato, tobacco and rice.