Since many secondary metabolites are generated in plants in response to external stimuli that may be physical, chemical, or microbial, in cultures, many fungal, yeast extracts and a number of organic and inorganic compounds have been found to induce secondary metabolite formation in cell and organ cultures. It appears that these elicitors may be giving the right stimulus to cells in cultures for the initiation of secondary metabolite production.

Adding Verticillium dahliae spores to cell cultures of Gossypium arboreum greatly enhanced gossypol yield. Likewise, in C. ledgeriana cultures there was an increase in anthraquinone production. In Pimpinella anisum cultures, coumarin synthesis was initiated by addition of Phytophthora. P. somniferum cell cultures accumulate sanguinarine when treated with a homogenate of the fungus Botrytis.

Addition of yeast extracts to Thalictrum rugosum cultures enhanced berberine content four times. Similarly, in Orthosiphon aristatus, there was a stimulation of rosmarinic acid production. Rhizoctonia solani increased production of sesquiterpenes in Agrobacterium rhizogenes transformed hairy-root cultures of Hyoscyamus muticus.

Supplementing media with sodium chloride, potassium chloride, and sorbitol individually increased catharanthine accumulation in cells of C. roseus. Addition of vanadyl sulphate increased production of catharanthine, serpentine, and tryptamine. Likewise addition of phenyl alanine to Lavendula cultures enhanced rosmarinic acid production. Copper sulphate addition to Lithospermum erythrorhizon cultures stimulated greater shikonin production. Colchicine application to Valeriana wallichii root cultures showed a 60-fold increase in valepotriates. Thiosemicarbazide promotes saponin biosynthesis over phytosterol production in Panax ginseng cultures.

Most cultures respond to an elicitor when included during the growth phase of the cells. For example, Papaver somniferum cell cultures are to be treated with solubilized chitin 6 days after culture initiation for optimal production of sanguinarine. Likewise, cultures of Eschscholtzia californica cultures had to be treated with yeast extract on the 6th day after culture initiation, for maximal production of benzophenanthridine alkaloids.