Plant Chemistry: An Internal Battle for Survival

Plant Chemistry: An Internal Battle for Survival

May 22, 2018

By: Jared Jacob, R&D Formulation Chemist

 

Chemical ecology is the “chemistry of biotic interaction”. Within the sphere of ecology, chemical ecology fulfills the niche that illustrates these intricate chemical models. The vast multiplicity of defense mechanisms within plants promotes survival in the midst of adverse environmental conditions, herbivore feeding, and pathogenic infection. An immune system, consisting mainly of a plant’s secondary metabolites as communicators and agents of defense, is intact within a plant to protect it. Plant secondary metabolites confer a host of protective properties. These very substances are the source of many of today’s nutraceuticals, vitamins, and wellness ingredients. Within the plant, they manifest as tannins, flavonoids, terpenes, and polyphenols; the latter three have been the subject of ongoing medical and industrial research.

 Allelopathy (Gk. “to suffer from each other”) is the means by which a plant biochemically changes its environment to increase survival and fitness (1). This aspect of biotic interference, either active [on demand--from de novo synthesis] or passive, significantly influences the plant’s surroundings. While competition is the removal or control of resources required for survival, allelopathy is the addition of materials for the purpose of changing life functions, to either “assist” or “impair” another organism (1). Some of these materials have an intrinsic degree of toxicity; those which render changes to the environment are termed allelochemicals (1).  Allelochemical communications affect several aspects of a plant’s environment, such as germination, root growth, infections, and insect (herbivore) wounding.   Four main classes of allelochemicals interactions exist: anti-biotics (microorganism to microorganism); kolines (plants to plants); marasmins (microorganisms to plants); and phytoncides (plants to microorganisms) (1). 

The phytoanticipin varieties of phytoncides are antimicrobial compounds innate to the plant, whereas, phytoalexins are synthesized de novo, from metabolic precursors, in response to pathogenic infection (2). Fungal, bacterial, viral, and nematode elicitors call upon the transcription [production] of these phytoalexins. Many plant structures are laden with complementary hair-like projections, known as trichomes, which help spread allelochemicals as an external layer of chemical defense (3). Trichomes become an added first line of defense against pathogenic or herbivore feeding, since many of the chemicals they exude are undesirable to the attackers.

Remarkable even of these sessile organisms, an effective system of immunity intact within plants affords them the ability to thrive. Through allelopathic interactions, plants are able to impair the life-functions of other plants, herbivores, and microbial invaders. Intricate mechanisms of signal transduction, specifically elicited by both wounding and pathogenic components, evoke plants’ defense responses in the form of phytochemical cascades. 

Human exploitation of allelochemicals secreted by one microorganism to another microorganism has allowed for the utility of antibiotic drugs (e.g. Penicillin) (1). Some phytoncidal allelochemicals, and others effective against environmental stressors, have proven to be powerful sources of therapies and antioxidants (e.g. resveratrol, phytocannabinoids, catechins, and certain terpenes), thus they have become incorporated into the modernized world’s regimen of nutritionals.

 

[1] Coder, K.D. (April 1999). Allelopathy in trees. Retrieved from http://www.forestry.uga.edu/outreach/pubs/pdf/FOR99-004.pdf

[2] Naoumkina, M, Farag, M.A., Sumner, L.W., Tang, W, & Liu, C.J. (2007). Different mechanisms for phytoalexin induction by pathogen and wound signals in medicago truncatula. Proceedings of the National Academy of Sciences of the United States of America, 104(46)

[3] Levin, D. A. (1973). The Role of Trichomes in Plant Defense. The Quarterly Review of Biology, 48(1, Part 1), 3-15. doi:10.1086/407484