In general, the compounds produced by plants have been divided into primary metabolites and secondary metabolites: Primary metabolites are simple sugars, amino acids, proteins, and nucleic acids which are directly required by plant growth 1 2. As their names suggest, primary metabolites are found in all plant cells and are the biomolecules underlying the existence of plants, like all other living things2.
Secondary metabolites are classified under 3 subtitles: alkaloids, terpenoids, and phenolics3. These materials traditionally called secondary metabolites are differentially distributed among limited taxonomic organizations in the plant kingdom. Secondary metabolites do not seem to participate in growth and development at first hand3. The primary metabolites, in contrast, such as phytosterols, acyl lipids, nucleotides, amino acids, and organic acids, are found in all plants and perform metabolic roles that are essential and usually obvious4.
While primary metabolites have a key position within the survival of the species, playing an active function within the photosynthesis and respiration, the absence of secondary metabolites does not result in immediate death, but instead in a long-term impairment of the organism’s survivability, often playing an important role in plant defense5. Those compounds are exceedingly numerous organizations of natural products synthesized via plants, fungi, bacteria, algae, and animals. Most secondary metabolites, such as terpenes, phenolic compounds and alkaloids are classified based on their biosynthetic origin. Different classes of these compounds are often associated with a narrow set of species within a phylogenetic group and constitute the bioactive compound in several medicinal, aromatic, colourant, and spice plants and/or functional foods5.
Secondary metabolites also deserve to be identified as organic molecules that ensure plant survival. Many functions as chemical signals in plants that make plants respond to stimuli, like the function of neurotransmitters in our nervous system. Others also perform tasks in defence, radiation protection, pollen dispersal, and more2.
However, secondary metabolites with this unique diversity are not always produced during the life of the plant. Their production occurs only in certain cells, tissues or organs at a certain stage of the plant’s development6. For example, phytoalexins are antimicrobial compounds produced only after injury. For this reason, they are very difficult to extract and purify, since they are synthesized in specialized cell types and at different developmental stages of the plant. As a result of this, secondary metabolites are produced by following different pathways such as biosynthetic production from primary metabolites and production in culture medium7.
In addition, some of the secondary metabolites are isolated from plants, creating the source of new drug possibilities to be discovered to fight cancerous diseases almost every year. One of the cancer drugs that is produced by secondary metabolites is Paclitaxel. It is mostly used for the treatment of breast, liver and ovarian cancer. Paclitaxel is isolated from the bark of the Taxus brevifolia (Pacific yew) tree8.
Another drug is Vincristine, which is obtained from the leaves of the Catharanthus roseus (Madagascar sea snail) plant9. The usage of Vincristine is approved in 1963 by the Food and Drug Administration (FDA). It has been used in adult chemotherapy, mainly in pediatric oncology practice against acute lymphoblastic leukaemia. It has been observed that its use in treatment increases the survival rate to around 80%. In conclusion, these complex molecules are suitable anticancer molecules that enable the development of a new clinical drug with new anticancer impact mechanisms.
- Croteau, Rodney, Toni M. Kutchan, and Norman G. Lewis. “Natural products (secondary metabolites).” Biochemistry and molecular biology of plants 24 (2000): 1250-1319.
- Bennett, Richard N., and Roger M. Wallsgrove. “Secondary metabolites in plant defence mechanisms.” New phytologist 127.4 (1994): 617-633.
- Erb, Matthias, and Daniel J. Kliebenstein. “Plant secondary metabolites as defences, regulators, and primary metabolites: the blurred functional trichotomy.” Plant Physiology 184.1 (2020): 39-52.
- Costa, T. D. S. A., et al. “Secondary metabolites.” Embrapa Agroindústria de Alimentos-Capítulo em livro científico (ALICE) (2012).
- Hartmann, Thomas. “Diversity and variability of plant secondary metabolism: a mechanistic view.” Proceedings of the 9th International Symposium on Insect-Plant Relationships. Springer, Dordrecht, 1996.
- Drew, Stephen W., and Arnold L. Demain. “Effect of primary metabolites on secondary metabolism.” Annual review of microbiology 31.1 (1977): 343-356.
- Sze, Daniel MY, Kristin Miller, and Brett Neilan. “Development of taxol and other endophyte produced anti-cancer agents.” Recent Patents on Anti-Cancer Drug Discovery 3.1 (2008): 14-19.
- Qu, Yang, Olga Safonova, and Vincenzo De Luca. “Completion of the canonical pathway for assembly of anticancer drugs vincristine/vinblastine in Catharanthus roseus.” The Plant Journal 97.2 (2019): 257-266.
Inspector: Süleyman ŞAHİN