Impaginato


special issue on plant and food metabolomic

this special issue has been realized with the contribution of the Regione toscana “pRaf 2012-2015

misura 1.2 e)” program, “profumi e sapori della toscana: dalla caratterizzazione del volatoma alla

valorizzazione dei prodotti alimentari di pregio (Volatosca)” project. 

foRewoRd

throughout the nineteenth century and for much of the twentieth century, the definition of secondary meta-

bolites simply meant that these substances, while present in plants, did not participate in the metabolic pro-

cesses essential to the life of the organism. they were defined as by-products of primary metabolism or as

excretory products or final products of metabolism, always pointing out that their irregular presence on plants

meant that they were not indispensable. over the last 50 years, knowledge in this area has been greatly expan-

ded, especially following the development of new isolation, separation and structural identification technolo-

gies (spectroscopy, nuclear magnetic resonance and mass spectrometry). the ease of structural identification

has expanded the number of secondary metabolites to reach the unthinkable number of 200000 for many of

which, however, remain uncertainty about their biochemical and physiological role. in recent years, however,

many researches have progressively clarified the role of these substances and some of them are known to

have a fundamental function. thus it has been for shikimic acid, for many years considered a simple metaboli-

te of Illicium anisatum, then revealed as a key molecule for synthesis of aromatic amino acids and, in turn, pre-

cursors of phenylpropanoids (flavonoids, coumarin, tannins and lignin). certainly these are not secondary func-

tions!

primary metabolism is essential to plants for growth and development, and secondary metabolism helps plants

to interact with the environment. many plant metabolites are also industrially important (e.g.: the physiologi-

cally active alkaloids used in modern medicine). these metabolites are produced by plants through complex

metabolic pathways.

among the researchers in this area it is inevitable to remember J.b. Harborne, who has been devoting some 50

years to the study of flavonoids and, more generally, to chemical ecology and  plant chemosystematics.

Harborne’s work has called for experimentation on all other classes of secondary metabolites, alkaloids, non-

protein amino acids, glucosinolates, lectins, terpenes, steroids, tannins, flavonoids, phenylpropanoids, lignins,

coumarin, waxes, etc. plant secondary metabolites are critical to various biological processes.

the plant’s specific organization has led it to produce a large amount of secondary metabolites and probably

selective pressure has left those molecules capable of conferring specific benefits to the plant: defense role

against animal, fungal and bacterial parasites, but also those molecules that allow to establish relationships

between plants of the same species or between different species.

numerous contributions to this special number of aHs are devoted to ecological biochemistry and that

explains the “non-secondary” role of so many metabolites; it is also hoped that the molecular biological tools

will spread to the labs in order to have accurate information on the genes involved in the various secondary

metabolism.

plant genomes are variously estimated  to contain 20000-60000 genes, and perhaps 15-25% of these genes

encode enzymes for secondary metabolism. still a lot of research work has to be done both physiologically and

biochemically on the secondary metabolism of many species, but i believe it is essential that laboratories use

data availability about the genes of Arabidopsis, an extraordinary model species, involved in secondary meta-

bolism.

thus, our knowledge of secondary metabolites, which have already made great advances over the last deca-

des, will make further progress in both physiological and biochemical and technological terms, confirming that

their traditional placement as “secondary metabolism products” was only due to lack of knowledge.

Amedeo Alpi