Why does the sunflower turn its head toward the sun? Why do some plants only bloom at night? Why are some plants more fragrant at certain times of the day? Part of the answer lies in one word: light.

More than just lighting, light acts as a signal, an energy source, and a biological clock for plants. It guides their growth, development, and behavior.

In this series of articles, we explore how light influences plants growth and survival. The first episode focused on the vital role of photosynthesis, the primary metabolic source for plants and the core of plant activity. The second one explored how light acts as a signal for plants to trigger many vital functions. In this third article, we’ll examine how light shapes the chemical composition of plants.

Episode 3: When light shapes plant chemistry

Unlike animals, plants are rooted in place.

They can’t escape drought, seek shade, or flee from herbivores or pathogens. To survive, they have evolved complex biochemical mechanisms to adapt to often hostile conditions.

Plants encounter various types of stress:

• Abiotic stress, caused by environmental factors such as extreme temperatures, drought, or excessive light.
• Biotic stress, caused by living organisms such as insect attacks, herbivory, fungi, or bacteria.

In both cases, plants trigger a cascade of biochemical responses to defend themselves, adapt, or communicate. These responses lead to the production of compounds known as secondary metabolites.

Among the many environmental signals, light can be a source of stress, a warning or communication signal that orchestrates the plant's chemistry. In this episode, we explore how light—through its intensity and quality (color)—influences the plant’s chemical makeup, especially in the production of secondary metabolites.

Secondary metabolites: chemical reactions in response to stress

Metabolites are the products of a plant’s biochemical reactions. We distinguish between:

Primary metabolites are essential for basic functions such as respiration, growth, and reproduction. For example, starch produced by photosynthesis is a primary metabolite.

Secondary metabolites are not strictly required for immediate survival but play a critical role in adaptation to stress and environmental interactions.

These secondary metabolites fall into three major categories:

• Terpenes : Volatile or non-volatile, often aromatic (e.g., menthol, limonene). Functions: Attract pollinators, repel herbivores, protect against UV radiation
• Phenolic compounds : Includes flavonoids, tannins, and phenolic acids. Functions: Antioxidants, pigments, defense against pathogens
• Nitrogen-containing compounds (alkaloids). Examples: Caffeine, nicotine, morphine. Functions: Toxic to herbivores, sometimes neuroactive

Other classification systems may include additional groups like betalains, glucosinolates, or glycosides, but the three main families—terpenes, phenolics, and alkaloids—cover the majority of known plant secondary metabolites.

Excess light: a source of oxidative stress

Photosynthesis—the foundation of plant life—relies on chlorophyll to capture light energy (see Article 1). But this process has its limits: when light intensity exceeds the plant’s capacity to use it, excess energy can impair photosynthesis. This is called photoinhibition.

This overload causes the accumulation of excited electrons, which can generate unstable molecules known as Reactive Oxygen Species (ROS).

These ROS can:

• Damage cellular membranes
• Degrade proteins
• Alter cellular DNA

This is known as oxidative stress.

To defend against this, plants ramp up the synthesis of protective secondary metabolites, particularly:

• Flavonoids: antioxidant pigments that trap ROS
• Anthocyanins: pigments that protect young leaves from UV rays, and also mitigate ROS to some extent

The case of UV: a danger for plants

Ultraviolet (UV) rays, though invisible to us, are well detected by plants—especially UV-B rays (280–315 nm). These rays can directly damage DNA and cause cellular mutations or lesions.

Plants sense UV through a specific receptor called UVR8, which activates defense mechanisms:

• Production of flavonoids, which act as natural sunscreens
• Synthesis of anthocyanins (red-purple pigments) that absorb UV and protect young tissues

For instance, sage (Salvia officinalis) produces rosmarinic acid via the shikimic acid pathway in response to intense UV stress.

This phenolic antioxidant helps defend the plant against UV-induced damage. Rosmarinic acid is highly sought after in cosmetic and pharmaceutical industries for its anti-inflammatory, antioxidant, antiviral, and anticancer properties (4).

Want to know more about sage and rosmarinic acid? Read our article

Light as a chemical signal for ecological interaction

Beyond immediate stress responses, light also acts as a master regulator, orchestrating the production of compounds that enhance ecological interactions.

Attracting pollinators at the right time

Some flowers emit complex floral scents rich in volatile terpenes specifically in response to light.

For example, jasmine produces aromatic compounds—like linalool or methyl jasmonate—in higher quantities at dawn, when blue light levels rise. This timing coincides with peak activity of pollinators, which are often early risers. Morning light acts as a trigger for volatile synthesis, ensuring that pollinators are attracted at the optimal time.

Defending against herbivores and pathogens

Depending on the type of light received (blue, red, UV…), plants can adjust the production of toxic, bitter, or repellent compounds:

• Toxin accumulation: Under UV or intense light, some plants produce more tannins or alkaloids, making leaves bitter or toxic. Example: Tobacco (Nicotiana tabacum) increases nicotine synthesis under UV-B—an alkaloid that is neurotoxic to insects.
• Pigment changes: Pigments like anthocyanins (red/violet) or carotenoids (orange/yellow) can deter herbivores visually by signaling toxicity or disrupting camouflage. Example: In some purple basil varieties, pigmented leaves are less consumed by aphids.
• Repellent floral scents: Light can also influence the production of defensive volatile compounds. Example: Nasturtium (Tropaeolum majus) emits sulfur-containing volatiles under light, creating a pungent odor that repels certain insect herbivores.

A system regulated by photoreceptors

These changes are orchestrated by specific photoreceptors:

• Cryptochromes and phototropins (sensitive to blue light)
• Phytochromes (sensitive to red and far-red light)
• UVR8 (for UV-B detection)

These photoreceptors activate genes involved in the biosynthesis of various secondary metabolites—depending on time of day, season, or light exposure. (See Article 2 for more information on photoreceptors)

Complex pathways influenced by multiple factors

Light is a key signal in regulating physiological processes in plants—especially in the biosynthesis of secondary metabolites. But it never acts alone. Factors like temperature, drought, wounding, pathogens, or soil conditions interact to shape a plant’s chemical profile.

A single pathway—such as the flavonoid, terpene, or alkaloid biosynthesis—can be activated by multiple signals. Example: Flavonoid synthesis can be triggered by UV light, water stress, or pathogen attack.

This shows how diverse stress signals—like UV rays, insect damage, or mechanical wounds—can converge, activating hormones that stimulate the same metabolic pathways.

A single pathway, such as that of rosmarinic acid, may thus be influenced by multiple environmental causes.

Mountain and alpine plants: champions of light adaptation

Some plants thrive in extreme environments where light is intense, temperatures are low, and air is thin.

These alpine or high-altitude species have developed extraordinary chemical strategies. In such settings, plants produce high concentrations of protective secondary metabolites:

• Flavonoids and anthocyanins to filter UV and reduce oxidative stress—often giving alpine plants their characteristic reddish or purplish hues.
• Tannins and terpenes to defend against insects and microbes, which can be especially aggressive in fragile ecosystems.

For instance, maca (Lepidium meyenii), a plant native to the Andes, produces macamides, unique nitrogen-based antioxidant compounds.
At Orius, we cultivated maca under various growth conditions and successfully enhanced the development of its hypocotyl (the storage organ between embryonic root and cotyledons), which is particularly rich in macamides.

Applications in controlled environments

Unlike open-field farming, controlled environments allow precise adjustment of light parameters—spectrum, intensity, and photoperiod—to:

• Increase the concentration of valuable metabolites
• Guide the synthesis of rare compounds
• Inhibit harmful substances (e.g., toxins, allergens)
• Modulate aromatic profiles
• Enhance plant resilience

That’s why at Orius, we’ve developed and patented our own lighting technologies, designed to serve biology and science—to produce plants of exceptional quality.

As described throughout this series, there’s no universal formula. Each plant responds differently to specific light spectra, intensities, and photoperiods. Every parameter can trigger a cascade of morphological and biochemical responses. It’s all about balancing yield, chemical quality, and plant resilience.

Conclusion

Light is far more than a source of energy—it’s a powerful lever that shapes a plant’s growth, form, flowering, sugar content, and internal chemistry. This internal chemistry enables plants to adapt, defend, and interact with their environment.

The very compounds that plants produce to protect themselves or attract—flavonoids, terpenes, alkaloids—have long fascinated and inspired humans in cosmetics, wellness, nutrition, and health.

Yet harnessing this plant chemistry is no simple task. Living systems don’t respond to on/off switches—they follow a complex logic, where every parameter influences the next.

We’ve worked with more than 60 plant species, tackling real-world challenges:

• Securing supply of rare or threatened species
• Enhancing concentrations of valuable actives
• Reducing risks from toxic compounds

When used wisely, light becomes a powerful tool to unlock the full potential of plants. Combined with other environmental factors—nutrition, temperature, humidity—it offers a vast field of innovation and a gateway to the future of plant science.

References

1. Jean Marc Sanchez. k.center. Le stress des plantes. 
2. Peixoto, Fernanda & Aranha, Ana Caroline & Nardino, Danielli & Defendi, Rafael & Suzuki, Rúbia. Extraction and encapsulation of bioactive compounds: A review. Journal of Food Process Engineering. (2022). 45. 10.1111/jfpe.14167.  
3.  Deviller, Geneviève. Traitement par lagunage à haut rendement algal (LHRA) des effluents piscicoles marins recyclés: évaluation chimique et écotoxicologique. (2003). 
4.  Guan H, Luo W, Bao B, Cao Y, Cheng F, Yu S, et al. A Comprehensive Review of Rosmarinic Acid: From Phytochemistry to Pharmacology and Its New Insight. Mol Basel Switz ;27(10):3292. (.2022) 
5. Li, J., Chen, L., Li, J., Duan, Z., Zhu, S., & Fan, L. (2017). The Composition Analysis of Maca (Lepidium meyenii Walp.) from Xinjiang and Its Antifatigue Activity. Journal of Food Quality, 2017, 1-7.