2.2.1 Basic Plant Biology and Ecology

In order to understand why, and in which parts, plants produce biologically active compounds, we must have a clear understanding of basic plant biology and how this relates to plant morphology. Plants, like fungi and animals, are eukaryotic organisms (i.e., their genetic material is bound within a cell nucleus and their cells possess membrane-bound “organelles” that are involved in producing chemical energy). However, plant cells are contained within a rigid cell wall, and multicellular tissues produce rigid organs that occupy space and acquire resources from the local environment. Plants are also the only eukaryotes to have chloroplasts (organelles specialized to perform photosynthesis). Thus, we could define plants as “a lineage of eukaryotic organisms exhibiting cell walls and chloroplasts”-a broad definition that includes everything from algae to Zygopetalum orchids.

The resources plants used to produce chemical energy and biomass are atmospheric carbon dioxide, light energy, and inorganic matter, including a range of minerals and water, which are used during photosynthesis in the chloroplasts. Oxygen is also used during respiration in the mitochondria to produce chemical energy. The thin gruel on which plants subsist imposes a relatively low-energy metabolism, and the rigid cell walls also contribute to a sedentary lifestyle, obliging terrestrial plants to spread via the dispersal of propagules, such as spores or seeds, or simply by clonal growth. A sedentary lifestyle also means that plants cannot flee their predators, which include various vertebrates, invertebrates, and microbes, from the largest land mammals to the tiniest viruses. Indeed, plants are the primary producers of biomass and energy in most terrestrial ecosystems, and thus have strong controlling effects on the resources available to the other organisms within ecosystems. It is for this reason that many plants, in the struggle to retain resources and energy, must defend their tissues. Producing biologically active compounds is one way of achieving this, and chemical means of defense, as we shall see later, may act against animals, microbes, and even other plants via a range of mechanisms.

Bacteria and fungi are also prodigious producers of specialized biologically active compounds, many of which, such as antibiotics, are the basis of significant modern therapies. However, the fact that plants are the major constituent of most ecosystems, they are sedentary, large enough for us to recognize and utilize, are easy and relatively safe to handle, and produce a range of biologically active compounds that can readily be extracted, means that plants offer the greatest potential as economically viable sources of active compounds.

Soure: Giacinto Bagetta, Marco Cosentino, Marie Tiziana Corasaniti, Shinobu Sakurada (2012); Herbal Medicines: Development and Validation of Plant-derived Medicines for Human Health; CRC Press

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