Chitosan as elicitor of health beneficial secondary metabolites in in vitro plant cell cultures.

Chitosan is an important structural component of the cell wall of several plant pathogen fungi. In plants, it can be applied in vivo as antimicrobial agent against fungi, bacteria and viruses, and in vitro can be used as elicitor of defense mechanisms. Its degrees of polymerization and of acetylation strongly influence the elicitation activity. Chitosan seems to be particularly effective in increasing the content of a large spectrum of plant polyphenols, such as stilbenes (i.e. resveratrol) and flavonoids (i.e. anthocyanins), very important antioxidants for plants, animals and humans. All these compounds, can be ingested by humans through daily diet and are absorbed in the small intestine, providing health benefits, such as increase of the antioxidant capacity of blood and potential prevention of cancer and cardiovascular diseases. In this chapter we present a comprehensive overview of the applications and effects of chitosan in plant cell cultures. Although the exact mechanism of chitosan action in plants is still unknown, different hypotheses have been proposed. Plant cell cultures have been viewed as a promising alternative to whole plant extraction for obtaining valuable metabolites, with the elicitation of the interesting compounds and the scale-up process as key points. In particular, in grape cell suspensions, the synthesis and release of several metabolites, were up-regulated by chitosan treatment. Concomitantly, the expression levels of some enzymes of the phenylpropanoid pathway as well as those of pathogen related proteins, together with the de-novo synthesis and/or accumulation of different proteins, were promoted. With the aim to further ameliorate the polyphenol yield, batch and fed batch grape cell fermentations were optimized also with the addition of chitosan, which proved to be highly effective in improving metabolite production in bioreactors.