UV Light on One Leaf Triggers Plant-Wide Antioxidant Defenses in Tobacco

Ultraviolet radiation is usually framed as a threat to plants, a form of light that damages DNA and triggers oxidative stress. But a growing body of research shows that moderate doses of UV can act as a beneficial signal, coaxing crops into producing protective compounds. Now, a team at the University of Pécs in Hungary has demonstrated something even more striking: when a single tobacco leaf is exposed to low-dose ultraviolet light, the entire plant appears to respond, with leaves that never saw a single UV photon mounting chemical defenses nearly identical to those of the irradiated leaf itself.

The study, published in Plant Cell Reports, focused on Nicotiana tabacum, the common tobacco plant long used as a laboratory model. Researchers led by Zoltán Katona and Éva Hideg exposed only the fourth true leaf of each plant to a broadband UV source filtered to remove wavelengths below 280 nanometers, delivering a biologically effective UV-B dose of 6.8 kilojoules per square meter over two days. The leaf directly above it, the fifth, remained completely shaded from UV. When the team later analyzed both leaves, they found that the unexposed systemic leaf had undergone biochemical changes that closely mirrored those in the treated leaf.

Two classes of molecules took center stage. The first were class III peroxidases, a large family of enzymes that plants deploy to manage reactive oxygen species and to reinforce cell walls. Using native polyacrylamide gel electrophoresis, the researchers separated seven distinct peroxidase isoforms from leaf extracts, labeled A through G according to their apparent molecular weights. In unexposed control plants, the dominant activities sat in the 40 to 75 kilodalton range, particularly isoforms C and D. After UV treatment, the pattern shifted: activities of isoforms D, E, F and G rose, while band C diminished, a reorganization that likely reflects either the selective activation of different peroxidase genes or altered post-translational glycosylation of the same gene products.

The remarkable finding was that the systemic fifth leaf, which had never been irradiated, displayed essentially the same peroxidase rearrangement as the directly exposed fourth leaf. This is the first demonstration that UV radiation can systemically reprogram the isoperoxidase profile of a plant, extending earlier work by the same group showing that low-dose UV raises antioxidant capacity and photosynthetic performance in leaves above the treatment zone. The team had previously implicated hydrogen peroxide as a mobile mediator of that systemic antioxidant effect, and the new results suggest the same signal cascade reaches deep into the plant’s enzymatic defense machinery.

Enzymes, however, are only half the story. Peroxidases need substrates to work on, and the second arm of the study examined the phenolic compounds that serve as both peroxidase substrates and direct antioxidants. Using high-performance liquid chromatography with diode array detection, the researchers profiled leaf extracts from four groups: directly UV-exposed leaves, systemic leaves, and the corresponding leaves of negative controls that received no UV at all and positive controls in which whole plants were irradiated at a fourfold higher dose for four days.

The chromatographic analysis revealed that chlorogenic acids dominated the phenolic pool, accounting for 80 to 97 percent of total extractable phenolics. These included 5-O-caffeoylquinic acid, the classic chlorogenic acid, along with its crypto- and neo-chlorogenic acid isomers. Even the modest, single-leaf UV dose increased total phenolic content by roughly 35 to 50 percent, and critically, the systemic leaf showed an increase of the same magnitude. Under the higher whole-plant dose, the effect was larger still, with chlorogenic acid itself showing the most pronounced rise.

Flavonoids told an even more dramatic story. Although they made up only 3 to 5 percent of phenolics in control leaves, they proved far more responsive to UV. Total flavonoid content tripled in the directly exposed leaves under the low-dose treatment and rose similarly in the systemic leaves. Under the four-times-higher whole-plant regimen, flavonoids surged approximately thirtyfold. The dominant flavonol was quercetin-3-O-rutinoside, accompanied by smaller amounts of quercetin-3-O-glucoside and kaempferol-3-O-rutinoside. The shift toward quercetin derivatives is biochemically meaningful: quercetins carry two hydroxyl groups on their B ring, making them substantially better antioxidants than the monohydroxylated kaempferols, and they absorb UV radiation effectively, shielding the leaf’s photosynthetic apparatus from below.

This quercetin bias is consistent with a well-established mechanism. UV exposure selectively activates the enzyme flavonoid 3′-hydroxylase, which redirects flux within the flavonoid pathway toward dihydroxylated compounds. Similar shifts have been documented in petunia, Arabidopsis and other species, and the same enzyme is known to respond to other stresses, including salinity, nutrient depletion and temperature extremes. That raises an important interpretive point for the Hungarian team: the systemic response may not be a UV-specific preparation but rather a general preemptive stress response, priming the whole plant against a broad range of challenges rather than narrowly fortifying against future ultraviolet exposure.

How the signal travels from the irradiated leaf to its unexposed neighbor remains an open question. The researchers consider local upregulation of phenolic biosynthesis in the systemic leaf, triggered by a mobile signal, more likely than physical transport of the phenolics themselves, since there is little evidence that colorless flavonols or phenolic acids are moved between tissues the way anthocyanins are shuttled into vacuoles. Hydrogen peroxide is the leading candidate messenger, supported by the team’s earlier work and by independent studies showing that hydrogen peroxide treatment stimulates phenylpropanoid biosynthesis genes in lettuce and differentially regulates peroxidase proteins in rice roots. But hormones, nitric oxide and calcium waves may also participate, and pinpointing the source of the systemic hydrogen peroxide, whether chloroplasts, peroxisomes or the apoplast, is a priority for future work.

The practical implications could be significant, particularly for controlled-environment agriculture. Because even a quarter of the acclimation dose produced measurable systemic benefits without harming photosynthesis, targeted low-dose UV treatment of a fraction of the plant canopy might be enough to elevate antioxidant and nutritionally valuable secondary metabolites across an entire crop. That would reduce energy costs and treatment time in vertical farms and greenhouses while boosting the resilience and quality of produce. Beyond agriculture, the study reinforces a broader biological message: plants do not operate as collections of autonomous leaves but as integrated networks, capable of coordinated, whole-organism responses that prepare tissues never touched by a stressor to withstand it. In the case of ultraviolet light, what happens to one leaf clearly does not stay on one leaf.

Subject of Research: Systemic UV-induced peroxidase and phenolic antioxidant responses in Nicotiana tabacum leaves

Article Title: Systemic induction of peroxidase and phenolic responses to UV radiation in Nicotiana tabacum

Article References: Katona, Z., Czégény, G., Csepregi, K., & Hideg, É. (2026). Systemic induction of peroxidase and phenolic responses to UV radiation in Nicotiana tabacum. Plant Cell Reports, 45(10), Article 292. https://doi.org/10.1007/s00299-026-03985-5

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03985-5

Keywords: ultraviolet radiation, systemic response, Nicotiana tabacum, peroxidase isozymes, phenolic profiles, chlorogenic acid, flavonoids, quercetin, antioxidant defense, hydrogen peroxide signaling, plant stress, controlled-environment agriculture