Practice question

Increasing secondary metabolite accumulation in plant cell cultures is commonly achieved by supplementation with elicitors after achieving adequate biomass. Secondary metabolism is resource costly competing with primary growth for carbon nitrogen and energy, regulated by growth defense trade off controlled by TOR kinase promoting growth versus SnRK1 promoting defense. Under normal culture high auxin low stress conditions flux stays in primary metabolism. Elicitor addition artificially activates jasmonate and salicylate mediated defense transcriptome inducing genes encoding rate limiting enzymes: phenylalanine ammonia lyase PAL for flavonoids rosmarinic acid, tryptophan decarboxylase for alkaloids, HMGR for terpenoids, and transcription factors ORCA3 in Catharanthus roseus regulating strictosidine synthase. Timing matters addition at late log phase prevents growth inhibition while maximizing product up to 10-20 fold. Combining elicitation with precursor feeding, media optimization reduced nitrogen, and permeabilizing agents DMSO enhances release. Industrial examples include methyl jasmonate raising paclitaxel in Taxus cell cultures, yeast extract raising shikonin in Lithospermum, chitosan raising berberine in Coptis, forming basis of biotechnological production of pharmaceuticals pigments and flavors in bioreactors.