Atropa belladonna: An Introduction to the Physiological Ecology of Deadly Nightshade

Commonly known as banewort, devil’s herb, and beautiful death, Atropa belladonna is native to Europe, North Africa, and Southwest Asia (Rita & Datta, 2011). In the United States and Canada, A. belladonna grows as a naturalised weed, thriving in disturbed soils of chalk and limestone (Rita & Datta, 2011). As excessive sunlight can stunt the plant’s development, A. belladonna proliferates most successfully amidst the shade of trees (Rita & Datta, 2011): the species flourishes in well-drained areas, preferring the friable debris of abandoned quarries and stony slopes of calcareous woodlands (Butcher, 1947). Accordingly, A. belladonna involves a number of unique adaptations, each contributing to the plant’s perenniality—with long, tapering roots, black berries, and various chemical defences, the species represents one of the world’s most striking and poisonous nightshades (Butcher, 1947).

Reaching heights of roughly 50–200 centimetres, A. belladonna features single, broadly ovate leaves, which alternate in asymmetric pairs (Butcher, 1947). Stems are terete and either glabrous or thoroughly covered in short, fine trichomes: the indumenta differ in density, and plants in full sun are often more pubescent than those in partial shade (Butcher, 1947). The tiny hairs are especially critical for individuals in exposed habitats, as they prevent desiccation and herbivory (Glas et al., 2012). Pentamerous flowers blossom from axillary buds, and concentrations of anthocyanin result in purple corollae; conspicuous sepals encircle the blooms, which accommodate both male and female organs, and yellow anthers curl about the stigma, attracting bumblebees and thrips (Butcher, 1947). Ovarian nectar further entices insect visitors, while self-pollination can also occur, as flowers tend to droop in pendulous arrangements (Butcher, 1947).

Ultimately, A. belladonna typically flowers between May and early September, while berries begin to ripen at the end of July (Butcher, 1947). Each fruit can hold approximately 120 seeds, and some berries cling to the plant through colder months, hanging from calyces into December (Butcher, 1947). Despite the plant’s toxicity, the flesh is devoured by birds, which serve as primary agents of seed dispersal (Butcher, 1947). Germination can take up to six weeks, and a notable period of dormancy occurs between September and March, resulting in a relatively slow process of filial growth (Butcher, 1947). Seedlings protrude from the soil, elongating from hooked positions: after they reach approximately 5 mm in height, the shoots unbend, and the cotyledons unfurl, becoming lanceolate from linear shapes before opening ovately (Butcher, 1947). Although reproduction largely depends on viable seeds, stolons are not unusual for A. belladonna, and fragments of the taproot can mature into sprouts, facilitating the plant’s persistence (Butcher, 1947).

Pharmacologically significant, A. belladonna synthesises several important compounds, including scopolamine and hyoscyamine: 13 tropane alkaloids reside within the roots, while seven occupy the surface-level tissues (Rita & Datta, 2011). Changes in climate dramatically influence the plant’s molecular processes: in sunny, dry environments, for example, alkaloids can constitute approximately 0.68% of the plant’s chemistry, a considerable increase from the 0.34% attributed to cool and rainy conditions (Rita & Datta, 2011). Proper sunlight, then, is imperative to the plant’s success. For instance, the organs of A. belladonna contain auxin (Rita & Datta), a hormone responsible for cell elongation (Johnston, 1940). As a growth regulator, auxin also promotes photosynthesis, affecting the plant’s movement as leaves turn to face the sun’s radiation (Johnston, 1940).

Two major biochemical processes are necessary for photosynthesis: energy transduction and carbon assimilation (Hardin & Lodolce, 2021). For energy transduction reactions, chlorophyll captures sunlight, which is converted to adenosine triphosphate and nicotinamide adenine dinucleotide phosphate (Hadin & Lodolce, 2021). ATP energy and NADPH reducing power are consequently established for the reactions of carbon assimilation, which synthesises carbohydrates from carbon dioxide (Hadin & Lodolce, 2021). Commonly known as the Calvin cycle, the process covalently joins carbon atoms to organic compounds, accomplishing reactions of carbon fixation (Hadin & Lodolce, 2021). Chloroplasts are crucial to both energy transduction and carbon assimilation reactions: without them, A. belladonna would not be able to produce the sugars, fats, and proteins upon which the plant’s survival depends (Hadin & Lodolce, 2021).

Like all land plants, A. belladonna contains both chlorophyll a and chlorophyll b: the pigments can harness a wide range of solar wavelengths, prompting photon absorption, which excites electrons and completes the first stage of photosynthesis: photoexcitation (Hadin & Lodolce, 2021). As water represents the electron donor for oxygenic phototrophs (Hadin & Lodolce, 2021), A. belladonna comprises a variety of specialised tissues, which function in both hydration and metabolism: stomata, for instance, allow the plant to regulate transpiration, closing amidst periods of drought and minimising water loss (Molles & Laursen, 2020). In essence, A. belladonna can resist desiccation by restricting stomatal openings during the day’s hottest and driest hours; additionally, the plant can limit the surface area of its leaves (Molles & Laursen, 2020), withering and curling towards the shade. Phylogenetically, vascular plants developed stomata as evolution carried botanical species inland (Khalil & Grace, 1592). Although the pores are integral to the plant’s tolerance of fluctuating moisture levels, photosynthesis ceases with stomatal closures; therefore, the mechanism of opening and closing stomata is only suitable for short-term water stress (Molles & Laursen, 2020).

Evidently, A. belladonna epitomises numerous examples of plant adaptations: its reproductive strategies accomplish efficient pollination and seed dispersal, while metabolic processes allow the plant to endure water scarcity and some instances of herbivory—cattle, for instance, are incapable of safely consuming the leaves and berries (Butcher, 1947). The multiple alkaloids of A. belladonna solidify the plant’s reputation as one of the deadliest poisons of antiquity (Rita & Datta, 2011). While the toxins can cause urinary retention, constipation, and death in humans, A. belladonna remains medicinally beneficial, ameliorating symptoms of asthma and Parkinson’s disease while offering narcotic solutions against nausea, pain, and mental illness (Rita & Datta, 2011).

References

Butcher, R. W. (1947). Atropa belladonna L. Journal of Ecology, 34(2), 345–353. https://www.jstor.org/stable/2256722

Glas, J. J., Schimmel, B. C., Alba, J. M., Escobar-Bravo, R., Schuurink, R. C., & Kant, M. R. (2012). Plant glandular trichomes as targets for breeding or engineering of resistance to herbivores. International Journal of Molecular Sciences, 13(12), 17077–17103. https://doi.org/10.3390/ijms131217077

Hardin, J., & Lodolce, J. P. (2021). Becker’s world of the cell. Pearson Education. Johnston, E. S. (1940). Sunlight and plant life. The Scientific Monthly, 50(6), 513–525. https://www.jstor.org/stable/16974

Khalil, A. A. M., & Grace, J. (1992). Acclimation to drought in Acer pseudoplatanus L. (sycamore) seedlings. Journal of Experimental Botany, 43(257), 1591–1602. https://doi. org/10.1093/jxb/43.12.1591

Molles, M. C., Jr., & Laursen, A. (2020). Ecology: Concepts and applications (5th Cdn. ed.). McGraw Hill.

Rawpixel. (2017). Illustration from Medical Botany, digitally enhanced from rawpixel's own original plates 11 [Illustration]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Illustration_from_Medical_Botany,_digitally_enhanced_from_rawpixel%27s_own_original_plates_11.jpg
This image is licensed under CC BY-SA 4.0.

Rita, P., & Datta, A. K. (2011). An updated overview on Atropa belladonna L. International Research Journal of Pharmacy, 2(11), 11–17. https://www.researchgate.net/ publication/284553281_An_updated_overview_on_Atropa_belladonna_L