Enhancing Anthocyanin Levels in Cannabis: Environmental Factors at Play

Many cannabis enthusiasts are lured by the vibrant pigments and hues found in cannabis cultivars. This article will emphasize anthocyanin production in cannabis cultivation, focusing on how cultivators can leverage environmental conditions and advanced lighting technologies to enhance plant health, aesthetic qualities, and phytochemical content.

What Are Anthocyanins?

It is widely known that the aesthetic allure of cannabis strains significantly contributes to their desirability among both consumers and cultivators alike. This is particularly evident in strains exhibiting a spectrum of vivid colors ranging from deep purples to blues and reds. The origin of these hues can be attributed to anthocyanins, a class of water-soluble compounds that belong to the part of the broader category of phenolic phytochemicals known as flavonoids. These pigments provide very versatile protection to plants, driven by various factors including temperature, humidity, and lighting conditions.

Anthocyanins have an anthocyanidin (aglycon) core structure bound to various 3- and 5- linked glycosides. There are six common anthocyanidins: cyanidin, delphinidin, malvidin, peonidin, petunidin, and pelargonidin.

These pigments are not exclusive to cannabis but are fairly common throughout the plant kingdom, especially in a wide array of fruits and vegetables, with blueberries being a prime example. The synthesis of these pH-sensitive pigments is a strategic adaptive response by plants to various environmental stimuli. They serve a vital role in plant defense mechanisms, enhancing resilience against a plethora of biotic (pathogenic attacks) and abiotic (drought, lack of nutrients, excessive light exposure) influences. Furthermore, anthocyanins have also been shown to elicit anti-diabetic, anti-carcinogenic, anti-inflammatory, and antimicrobial properties in the human body (1). The antioxidative properties of these compounds primarily stem from their innate ability to scavenge harmful oxidants like reactive oxygen species (ROS)—volatile molecules present in the environment capable of causing cellular and tissue damage, resulting in various health disorders over time. By neutralizing these reactive species, antioxidants mitigate the harmful impacts induced by these free radicals (2).

Environmental and Genetic Factors

The synthesis of anthocyanins in cannabis is a multifaceted process that is reliant upon various genetic and environmental factors that influence the stability and intensity of anthocyanin pigments. These factors include, but are not limited to, the structure and concentration of pigments, pH levels, temperature, and both the intensity and quality of light. These components interact in a complex, synergistic manner to foster an optimal environment that promotes growth. Understanding these mechanisms is crucial for both breeding and cultivation practices aimed at enhancing desired traits in cannabis, including coloration for aesthetic or consumer purposes, as well as potentially influencing the plant’s therapeutic properties.

pH Levels

Anthocyanins are characterized by four different structures, which exist in equilibrium and vary with pH levels. At low pH (<2), the flavylium cation predominates, exhibiting red or orange hues. Conversely, at elevated pH levels a rapid proton loss occurs, there is a decrease in flavylium cation concentration, accompanied by an increase in quinoidal base, carbinol pseudobase, and chalcone forms. This shift in the structural forms results in alterations in the molecular descriptors of the anthocyanin molecule, such as the number of hydroxyl groups, the presence of a double bond on flavonoid C ring, and the bond dissociation energy of hydrogen (3).

Temperature

Exposure to low-temperature conditions can induce oxidative stress in plants, leading to an increase in the expression of genes associated with anthocyanin synthesis. The “Croptober” period—October’s harvest time for outdoor cannabis cultivation—serves as an example of this phenomenon. This upregulation results in increased accumulation of anthocyanins which in turn improves plant resilience to cold temperatures, functioning akin to an antifreeze to safeguard cellular integrity. Due to the increased number of anthocyanins produced by the plants, the coloration of leaves and buds intensifies with hues of purples, red, and blue. In contrast, higher temperatures tend to reduce anthocyanin levels leading to less vibrant plant pigments (1). From a horticultural and aesthetic standpoint, this stress-induced coloration can be beneficial. It is valued for its intrinsic aesthetic value as well as its use as a tool for identifying and judging quality. It’s important to note that the ability to produce vibrant colors through enhanced anthocyanin production depends on the genetic makeup of the cannabis strain. Some strains are genetically predisposed to produce high levels of anthocyanins, while others may show little change in coloration under the same conditions.

Phytohormones

Beyond environmental stimuli, the synthesis of anthocyanins is also governed by a range of internal factors such as plant hormones. These small molecular compounds are crucial in managing various physiological and developmental processes within plants, including growth patterns, and responses to both biotic and abiotic stressors. Research indicates that plant hormones play a significant role in the regulation of anthocyanin synthesis, influencing it either positively or negatively. For example, abscisic acid is known for its role in regulating growth, development, and stress adaptation in plants and it has been observed to promote anthocyanin formation in leaves and various fruits including apples and sweet berries. Salicylic acid—another vital hormone—boosts plant immunity and is linked to increased anthocyanin levels and grapes, pomegranates, and Arabidopsis. In contrast, ethylene—a hormone integral to processes such as plant growth, aging, fruit maturation, and stress adaptation—has been found to suppress anthocyanin levels under certain conditions. Studies with Arabidopsis have demonstrated that ethylene impedes the anthocyanin production stimulated by sucrose and light exposure (4).While plant hormones have been shown to either trigger or inhibit anthocyanin synthesis in reaction to stress, the precise molecular mechanisms that govern this regulatory pathway call for further investigation.

Nutrients

Anthocyanin concentrations significantly fluctuate based on genetic makeup, mineral content, and nutritional supplementation which are crucial for plant growth, tissue repair, reproduction, and overall vitality. Plants require 17 essential nutrients with primary macro nutrients like nitrogen, phosphorus, and potassium needed in larger quantities. A deficit in these nutrients can adversely influence anthocyanin synthesis, yet research exploring this relationship remains sparse (5). Increased levels of anthocyanins are not solely indicative of nitrogen or phosphorous deficiencies, as they may arise from various of other nutritional imbalances (6). Some species consistently display these pigments as an inherent characteristic of their phenotype, irrespective of external stressors, whereas others do not exhibit these colors at any point during their life cycle. This can be a common oversight, yet it is imperative to recognize that when plants exhibit certain symptoms, it may be a signal of deficiency, which will invariably impact the ultimate yield of the crop. To maximize growth, soil testing, plant analysis, and growth comparisons should be conducted to understand and tailor nutrient management strategies.

Light

Light quality, intensity, and duration are paramount variables within any cultivation environment, significantly influencing epigenetic modifications. The use of different lighting methods strategically can influence the composition of phytochemicals, possibly changing how anthocyanins are expressed in subsequent generations. This underscores the critical role of light in modulating plant biochemical pathways and genetic expression, thereby shaping the phenotypic characteristics of cannabis. Different light wavelengths can either promote or inhibit anthocyanin production. Phytochrome and cryptochrome, which are photoreceptors, perceive red and blue light spectra, respectively. This detection initiates the start of transcription processes that drive the biosynthesis of flavonoids, including anthocyanins. The resulting anthocyanin pigments endow plants with a myriad of beneficial protective attributes such as antioxidation, photoprotection, and thermal dissipation capabilities.

Intense lighting exposure can induce oxidative stress in plants via various mechanisms. Overexcitation of the plant’s photosystem results in more energy being absorbed than photosynthesis systems can utilize. This is colloquially referred to by cannabis cultivators as “lighting saturation.” Excess electrons transfer to oxygen molecules, producing ROS such as superoxide anions and hydrogen peroxide. ROS can damage lipids, proteins, and may even alter or otherwise damage plant deoxyribonucleic acid (DNA) (7-8). Anthocyanins directly absorb this radiation, particularly in the blue and ultraviolet (UV) spectra, reducing photoreceptor excitation and therefore, reducing the production of ROS. In addition to this prophylaxis, anthocyanins perform as powerful antioxidants, reducing oxidative stress and preventing cellular damage (9).

Anthocyanin concentrations in tissues serve as filters for incoming light, further protecting the photosystems from overload or damage (photoinhibition). In addition, this buildup assists in thermal dissipation, cooling plant tissue and maintaining cellular integrity (10). The temperature of plant tissues, which can vary among different strains, affects the rate of transpiration and the plant’s ability to regulate its internal water balance. Consequently, this variation can lead to inconsistencies in vapor pressure deficit (VPD). Isolating one strain per cultivation environment emerges as a strategic approach to control VPD more accurately, catering to the specific needs of each strain and thereby optimizing overall cannabis cultivation outcomes.

Lighting Spectrum

UV and Blue Light

UV photoreceptors (UVR8) and cryptochrome photoreceptors instigate signaling for transcription leading to production of anthocyanins. Transcription protein factors regulate genes in biosynthetic pathways, increasing anthocyanin production (11).

Green Light

Although not directly involved in the production of anthocyanins, green light has a profound impact on production of this pigment. Green light more readily passes through a plant canopy and is perceived by plants as “shading.” Shading is perceived by the plant as a reduction of available blue and red light wavelengths and an increase in far-red wavelengths (12). Responses to shading can be changes to plant morphology, such as via phototropism (changes in leaf and stem orientations to increase lighting exposure), elongation/growth to “reach” for lighting and reduction of branching at lower canopy levels (13). Plants may also respond by altering their biochemical pathways, increasing chlorophyll and anthocyanin production and altering hormone levels, which regulate growth responses (14).

Red and Far-Red Lighting

Red and far-red lighting directly and significantly influence anthocyanin production in various ways. Red and far-red light create a reversible conversion in phytochrome photoreceptors. Red light creates the active phytochrome form “Pfr,” increasing anthocyanin production. Far-red light converts these phytochrome receptors back to the inactive form “Pr.” This reversion reduces anthocyanin production. As mentioned earlier, a high far-red to red light ratio is interpreted by the plant as “shading” and in essence, this condition deprioritizes anthocyanin production in favor of a morphological approach to protecting the plant (15).

Conclusion

This article examined the intricate interplay between anthocyanin production and cannabis cultivation, shedding light on how these pigments contribute significantly to the aesthetic and therapeutic benefits of cannabis. By understanding the genetic and environmental factors that influence anthocyanin synthesis including temperature, pH, phytohormones, nutrients, and lighting, cultivators can employ advanced techniques to enhance these traits. Manipulating these elements can lead to cannabis strains with unique pigments and therapeutic properties. Research into anthocyanin production unveils regulatory networks that influence pigment production and how they help plants respond to environmental stress, improving resilience. This knowledge enables selective breeding practices to fine-tune both aesthetic and therapeutic traits. A deeper understanding of anthocyanin biosynthesis—its genetic and environmental influences—highlights the sophisticated approaches necessary in cannabis cultivation to achieve desired phenotypic expressions. Cutting-edge research in anthocyanin production presents exciting opportunities for developing cannabis strains that cater to the needs of consumers and patients alike, highlighting the dynamic and ever-expanding field of cannabis cultivation.

References

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About the Columnist

Dr. Zacariah Hildenbrand is a research Professor at the University of Texas at El Paso, the principal founder of Inform Environmental, a partner of Medusa Analytical, and is a director of the Curtis Mathes Corporation (OTC:CMCZ). Direct correspondence to: zlhildenbrand@utep.edu.

About the Guest Co-Authors

Hannia Mendoza-Dickey has an MS degree in Chemistry and is the founder of Green Matter Consulting. hemendoza0816@gmail.com.

Robert Manes is the CEO and CTO of the publicly-traded Curtis Mathes Corporation, where he specializes in the creation and manufacture of frequency-specific lighting for horticulture and phototherapy purposes.

How to Cite This Article:

Hildenbrand, Z., Mendoza-Dickey, H., Manes, R., Shining a Light on Cannabis Photobiology, Cannabis Science and Technology, 2024, 7(2), 14-17.