Plant in vitro cultures represent an attractive and cost-effective alternative to classical approaches to plant secondary metabolite (PSM) production (the “Plant Cell Factory” concept). Among other advantages, they constitute the only sustainable and eco-friendly system to obtain complex chemical structures biosynthesized by rare or endangered plant species that resist domestication. For successful results, the biotechnological production of PSM requires an optimized system, for which elicitation has proved one of the most effective strategies. In plant cell cultures, an elicitor can be defined as a compound introduced in small concentrations to a living system to promote the biosynthesis of the target metabolite. Traditionally, elicitors have been classified in two types, abiotic or biotic, according to their chemical nature and exogenous or endogenous origin, and notably include yeast extract, methyl jasmonate, salicylic acid, vanadyl sulphate and chitosan. In this review, we summarize the enhancing effects of elicitors on the production of high-added value plant compounds such as taxanes, ginsenosides, aryltetralin lignans and other types of polyphenols, focusing particularly on the use of a new generation of elicitors such as coronatine and cyclodextrins.

Withania somnifera, commonly known as Ashwagandha, is an important medicinal plant that has been used in Ayurvedic and indigenous medicine for over 3,000 years. In view of its varied therapeutic potential, it has also been the subject of considerable modern scientific attention. The major chemical constituents of the Withania genus, the withanolides, are a group of naturally occurring C28-steroidal lactone triterpenoids built on an intact or rearranged ergostane framework, in which C-22 and C-26 are appropriately oxidized to form a six-membered lactone ring. In recent years, numerous pharmacological investigations have been carried out into the components of W. somnifera extracts. We present here an overview of the chemical structures of triterpenoid components and their biological activity, focusing on two novel activities, tumor inhibition and antiangiogenic properties of withaferin A and the effects of withanolide A on Alzheimer's disease. The most recent attempts in biotechnological production of withanolides are also discussed.

Taxol is one of the most effective anti-cancer drugs ever developed. The natural source of taxol is the inner bark of several Taxus species, but it accumulates at a very low concentration and with a prohibitively high cost of extraction. Another problem is that the use of inner bark for taxol production implies the destruction of yew trees. For all these reasons, the growing demand for taxol greatly exceeds the supply that can be sustained by isolation from its natural source and alternative sources of the drug are being sought. Although taxol has been prepared by total synthesis, the process is not commercially viable. Taxol can also be semisynthetically produced via the conversion of baccatin III or 10-deacethylbaccatinIII found in Taxus needles but the cost and difficulty of the extraction process of the semisynthetic precursors are also very high. The most promising approach for the sustainable production of taxol and related taxoids is provided by plant cell cultures at an industrial level. Taxol is currently being clinically used against different tumour processes but due to the difficulty of its extraction and formulation, as well as the growing demand for the compound, new taxol analogues with improved properties are being studied. In this revision we discuss current research in the design of new taxol-related compounds, the chemical structure/anti-cancer activity relationship and new formulations of the drug. We also consider the optimizing strategies to improve taxol and related taxoid production in cell cultures, as well as the current knowledge of taxol metabolism, all of which are illustrated with examples, some of them from our own research.