How Plants Produce Terpenes: The Biochemistry Behind Secondary Metabolite Production

Terpenes are not added to plants from outside. Plants build them internally, in specialized cellular compartments, from simple precursor molecules, using enzyme systems encoded in the plant's own genome. Understanding how this biosynthesis works explains what growers can realistically influence and why certain organic inputs are relevant to the process.

Secondary metabolites is the broader category. Terpenes, phenolics, alkaloids and other aromatic compounds are all secondary metabolites — not directly involved in the core functions of growth and reproduction but critical for defense, pollinator attraction and environmental adaptation. Terpenes are the largest and most structurally diverse group.

Why plants make terpenes

Plants cannot run away from herbivores, pathogens or competitors. Secondary metabolites are their chemical arsenal. Terpenes serve multiple functions: deterrence of insect herbivores, attraction of pollinators and seed dispersers, inhibition of competing plants through allelopathy, and signaling between plant tissues during stress responses.

In plants with dense glandular trichome production, terpene accumulation is particularly high because the trichomes serve as the primary site of both biosynthesis and storage. The sticky, aromatic resin produced in glandular trichomes functions as a physical and chemical deterrent against insect feeding and pathogen colonization.

The plant does not produce terpenes for human benefit. It produces them for its own survival. The grower's job, from a terpene production standpoint, is to understand what biological signals and nutritional conditions allow the plant to run these pathways at their fullest capacity.

The two terpene biosynthesis pathways

All terpenes are built from a five-carbon isoprene unit. The two pathways that produce these building blocks are physically separated in the plant cell.

The MEP pathway (methylerythritol phosphate pathway)

Also called the non-mevalonate pathway or the DXP pathway. Located in plastids, primarily chloroplasts. This pathway produces the isoprene units IPP (isopentenyl pyrophosphate) and DMAPP (dimethylallyl pyrophosphate) from pyruvate and glyceraldehyde-3-phosphate, compounds from photosynthesis.

From IPP and DMAPP, the pathway builds GPP (geranyl pyrophosphate), the C10 precursor to monoterpenes. Terpene synthase enzymes — a large family of enzymes encoded by TPS genes — then catalyze the conversion of GPP into specific monoterpenes.

Monoterpenes (C10) from the MEP pathway include: limonene, myrcene, linalool, alpha-pinene, beta-pinene, terpinolene, geraniol, ocimene and others. These are the primary aromatic terpenes in flowering plants. Their small size and high volatility make them the dominant contributors to aroma profiles.

The MVA pathway (mevalonate pathway)

Located in the cytoplasm and endoplasmic reticulum. This is the evolutionarily older pathway, shared with animals and fungi. It builds IPP and DMAPP from acetyl-CoA through a series of enzymatic steps, with HMG-CoA reductase as the key regulated enzyme.

From IPP and DMAPP, the MVA pathway builds FPP (farnesyl pyrophosphate), the C15 precursor to sesquiterpenes. Sesquiterpene synthases then convert FPP into specific sesquiterpenes.

Sesquiterpenes (C15) from the MVA pathway include: beta-caryophyllene, alpha-humulene, farnesene, bisabolene, germacrene and others. These are less volatile than monoterpenes and contribute lower, woodier, spicier notes to the overall aromatic profile.

The separation matters

Because the two pathways are compartmentally separated, they are regulated independently. Environmental inputs affect them differently. Light quality (specifically UV-B) primarily influences MEP pathway flux and monoterpene production. Jasmonate signaling (from insect damage or mechanical stress) upregulates both pathways but through different mechanisms. Temperature influences terpene volatility and the rate of terpene synthase activity.

There is some exchange of precursor units between the pathways through the plastid envelope, so the separation is not absolute. But for most purposes, conditions that increase monoterpene production and conditions that increase sesquiterpene production are somewhat distinct and can be addressed somewhat independently.

Where terpene biosynthesis happens

The majority of terpene production in resinous flowering plants occurs in glandular trichomes, specifically the secretory head cells at the tips of stalked trichomes. These cells are specialized for terpene synthesis and storage. They contain dense plastid populations (supporting MEP pathway activity) and significant smooth endoplasmic reticulum (supporting MVA pathway activity).

The trichome head accumulates terpenes in a subcuticular space, the cavity between the cell walls and the outer cuticle of the secretory cells. This is the resin that coats the flower surface.

Trichome density (number of trichomes per unit of surface area) and trichome size both influence total terpene production capacity. Genetics determines the potential. Environmental and nutritional conditions determine how close to that potential the plant runs.

What influences MEP and MVA pathway flux

Light. UV-B radiation activates chalcone synthase and related enzymes that share regulatory pathways with terpene biosynthesis. UV-B increases monoterpene production in documented horticultural research. Full-spectrum light sources with UV output support higher terpene expression than narrowband LED-only systems.

Temperature. Cooler nighttime temperatures in late flower serve two functions: they slow terpene volatilization (keeping terpenes in the resin rather than evaporating off) and they influence enzyme activity rates in ways that can concentrate aromatic compounds. The standard recommendation is a 10-15F day-to-night temperature differential in the final weeks.

SAR activation. Salicylic acid signaling broadly upregulates secondary metabolite production including terpene biosynthesis through transcriptional activation of TPS genes and related biosynthetic genes. This is the mechanism behind aloe vera's role in advanced FFJ formulas.

Nitrogen form and availability. Terpene synthase enzymes are proteins. Building and maintaining the enzymatic machinery of terpene biosynthesis requires nitrogen. Free amino acid delivery during peak flowering provides this nitrogen efficiently without triggering the vegetative nitrogen response that can dilute secondary metabolite concentration.

Rhizosphere health. Consistent mineral access through an active microbial rhizosphere ensures the plant has trace minerals required as cofactors in terpene biosynthesis enzymes. Magnesium, iron and sulfur are all cofactors in secondary metabolic pathways. A depleted or biologically inactive rhizosphere creates mineral access bottlenecks that limit terpene production below the plant's genetic capacity.

What growers cannot change

Genetics determines the terpene synthase gene repertoire. A plant with no myrcene synthase gene does not produce myrcene regardless of what inputs you apply. The genetic terpene profile is set at germination.

What environmental and nutritional management changes is the expression of that profile — how much of the genetic potential is realized. A well-supported plant running all its biosynthesis pathways efficiently produces more of its own terpenes than a poorly supported plant with identical genetics.

For the practical grower application of this science, see our guide to supporting terpene production.