**Author details**

culture medium [155]. Cocaine production was nearly an order of magnitude greater on Anderson rhododendron medium (ARM) [156], Gamborg B5 (GB5) [157], and Murashige– Tucker medium (MMT) [158], but the amounts produced on MMT and GB5 were not signifi‐ cantly different from each other. Cinnamoylcocaine was affected in the same way. The major factor controlling tropane alkaloid (TA) accumulation was medium composition, with cocaine levels on ARM being nearly an order of magnitude greater than on the other media. Many nutrients, including cobalt, copper, molybdenum, calcium, magnesium, iron, boron, iodine, manganese, zinc, and myo–inositol, and the growth regulators and the ammonium:nitrate ratio are at equivalent levels in ARM as in one of the other media, and can therefore be excluded as factors promoting TA accumulation. However, a number of factors differed between ARM and the other media, and might be responsible for the elevated TA content. Total ion concen‐ tration is lower in ARM, and could be an important factor given the importance of salt content in controlling secondary metabolism [155]. Nitrate concentration was also lower in ARM, and there are numerous reports in the literature of an inverse relationship between nitrate availa‐ bility and accumulation of secondary metabolites in many plant species, including *Arabidopsis thaliana* [159], *Hordeum vulgare* [160], and *Nicotiana tabacum* [161]. Similarly, the reduction of nitrate concentration in the culture medium of *Atropa belladonna* hairy roots increases alkaloid content [162]. In regards to CGA, the media were all significantly different from each other with the lowest production on ARM and highest on MMT. Less CQA was produced on ARM than on either of the other two media, which did not differ from each other [155]. Apart from these characteristics, the efficiency of elicitation also depends on elicitor specificity, cell line or clones of microbial elicitor used the presence of growth regulators, nutrient composition of the

262 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

The development of plant tissue cultures for the production of secondary metabolites has been underway for more than three decades. Although there are well–established plant tissue culture techniques, their application to large scale production is still limited to a few processes. Various stimulation and process strategies have been exercised to improve secondary metab‐ olite production in plant tissue cultures. Elicitation has been widely applied for enhancement of secondary metabolite production in plant cell and organ cultures. The effects of various abiotic and biotic elicitors on secondary metabolite production in plant tissue cultures are dependent on the specific secondary metabolites. The exploration of the production of useful secondary metabolites through regulation of biosynthetic pathway of the various plant cell and tissue cultures of medicinal plants has been carried out by a group of plant scientists in several countries during the last decade. Although, elicitation enhances secondary metabolism in plant cells in vitro, but the exact mechanism is not exactly understood. There is a tremendous scope for the large–scale production of secondary metabolites in the plant tissue culture system

medium, and the environmental conditions.

by using the elicitors as an agent.

**8. Conclusion**

Poornananda M. Naik and Jameel M. Al–Khayri\*

\*Address all correspondence to: jmkhayri@yahoo.com; jkhayri@kfu.edu.sa

Department of Agricultural Biotechnology, College of Agriculture and Food Sciences, King Faisal University, Al–Hassa, Saudi Arabia
