Lupin Leaf Extract Triggers Oxidative Stress and Enzyme Collapse in Two Common Weeds

Aqueous leaf extract of Lupinus termis, the white lupin familiar to farmers and gardeners across the Mediterranean region, has emerged as a surprisingly potent chemical weapon against two widespread agricultural weeds. In a study published in Plant Biosystems, a research team led by Hamed M. El-Shora of Mansoura University and corresponding author Gharieb S. El-Sayyad of Imam Mohammad Ibn Saud Islamic University examined how lupin leaf extract disrupts the physiology of Euphorbia helioscopia, a member of the spurge family, and Chenopodium murale, a nettle-leaved goosefoot now classified in the amaranth family. Both species are stubborn weeds of crop fields in Asia, North Africa and beyond, and both have evolved considerable resilience to conventional control measures. The new work suggests that the lupin’s chemistry can overwhelm that resilience, but only up to a point, and that the dose determines whether the target weeds mount a defense or simply collapse.

Allelopathy, the phenomenon in which plants release biochemicals that suppress or stimulate their neighbors, has fascinated ecologists for decades and is increasingly viewed as a source of environmentally benign herbicides. Allelochemicals, which include phenolic acids, flavonoids and other secondary metabolites, interfere with germination, photosynthesis, respiration and nitrogen assimilation in susceptible species. What distinguishes the new study is its effort to connect the full chain of events, from the first burst of reactive oxygen species to the activities of specific enzymes of nitrogen metabolism and the phenylpropanoid pathway, in two weed species that had never previously been analyzed together under lupin allelopathy. The authors argue that this integrated view is essential if allelopathic plants are ever to be deployed deliberately as bioherbicides rather than admired as botanical curiosities.

The team grew seedlings of both weeds and treated them with aqueous leaf extract of Lupinus termis at a range of concentrations, then measured a battery of indicators spanning seed germination, oxidative stress markers, antioxidant defenses and metabolic enzyme activities. The earliest and most striking signal was oxidative. Levels of malondialdehyde, the standard fingerprint of lipid peroxidation, rose markedly in the leaves of both species, as did the concentrations of superoxide radicals and hydrogen peroxide. These reactive oxygen species are normal byproducts of a working metabolism, but when their production outpaces their removal they attack membranes, proteins and nucleic acids. The accumulation of all three markers after extract treatment indicated that the allelochemicals in lupin leaves had pushed the weeds’ cellular chemistry into a state of genuine oxidative stress rather than a transient, easily buffered fluctuation.

Plants are not defenseless against such assaults, and the study documented the weeds’ countermeasures in detail. Total phenolic and flavonoid contents increased pronouncedly in both species following exposure to the lupin extract, a defensive metabolic adjustment that reflects activation of the phenylpropanoid pathway, the assembly line that converts phenylalanine into a diverse arsenal of protective compounds. Phenolics can directly scavenge radicals, chelate metal catalysts of oxidation and reinforce cell walls, so their accumulation is a classic sign that a plant perceives chemical stress and is investing resources in containment. The researchers also tracked the four central enzymes of the antioxidant system: superoxide dismutase, which converts superoxide radicals into hydrogen peroxide; ascorbate peroxidase, which uses ascorbate to reduce that peroxide inside chloroplasts; catalase, which decomposes peroxide in peroxisomes; and glutathione reductase, which regenerates the reduced glutathione that feeds the ascorbate-glutathione cycle.

The behavior of these enzymes turned out to be sharply concentration-dependent, and this is where the study delivers its most instructive twist. At lower concentrations of the lupin extract, the activities of superoxide dismutase, ascorbate peroxidase, catalase and glutathione reductase were markedly stimulated in both weed species, suggesting an adaptive response to moderate oxidative stress in which the antioxidant machinery is upregulated to match the increased radical burden. At higher concentrations, however, the same enzymes were significantly suppressed, indicating direct inactivation or structural damage under excessive allelochemical pressure. In other words, a modest dose of lupin chemistry acts like a training exercise that the weeds can withstand, while a heavy dose disables the very enzymes that would otherwise save them. This biphasic pattern mirrors findings from other allelopathy systems and underscores why concentration control matters enormously in any practical application.

Photosynthetic pigments provided a second window into the damage. The study assessed chlorophylls and carotenoids in the treated leaves, following the established understanding that allelopathic phenolics can inhibit chlorophyll accumulation both by suppressing its synthesis and by accelerating its degradation through enzymes such as chlorophyllase. Pigment loss compounds the oxidative problem, because chloroplasts are simultaneously the main source of reactive oxygen species under stress and a primary victim of them. When the photosynthetic apparatus is compromised, energy interception becomes inefficient, excitation pressure builds in the light-harvesting complexes, and the resulting electron leakage generates still more superoxide. The combination of declining pigments and rising lipid peroxidation in the treated weeds paints a coherent picture of a photosynthetic system under escalating, self-amplifying stress.

Beyond the antioxidant story, the researchers extended their analysis to nitrogen metabolism, an angle that gives the work much of its originality. Nitrogen assimilation depends on a chain of enzymes including nitrate reductase, glutamine synthetase and glutamate synthase, which together convert soil nitrate into the amino acids from which proteins, nucleic acids and chlorophyll are built. Perturbing this chain starves a plant of the building blocks needed to repair stress damage, creating a second front of vulnerability. The study’s novelty, according to the authors, lies precisely in linking the concentration-dependent oxidative stress responses with alterations in nitrogen metabolism and in the enzymes of the phenylpropanoid pathway, thereby showing how a single allelochemical insult reverberates through several biochemical networks at once rather than hitting one target in isolation.

The implications for weed management are considerable. Synthetic herbicides face mounting problems of resistance, residues and regulatory restriction, and allelopathy is repeatedly proposed as a source of bioherbicides and of crop rotations that naturally suppress weeds. Lupinus termis is already cultivated as a grain and forage legume, so its residues are abundantly available as mulch, extract or soil amendment. If the concentration-dependent pattern observed here holds in field settings, lupin-derived preparations could be tuned to push target weeds past the threshold where their antioxidant defenses fail, while the same chemistry at lower intensity might even prime neighboring crops. The authors are careful to frame the work as a foundation: the study is the first to examine lupin leaf extract against these two species together, and translating the greenhouse biochemistry into agronomic practice will require dose calibration, soil chemistry considerations and validation against non-target organisms.

The research also contributes to a broader mechanistic debate about how allelochemicals actually work. Recent reviews have emphasized that perturbation of reactive oxygen species metabolism is a recurring element in the mode of action of many allelochemicals, and the lupin study fits that framework neatly while adding metabolic depth. The biphasic enzyme response suggests that hormesis, the phenomenon in which low doses of a stressor stimulate and high doses inhibit, may govern not only growth but the antioxidant apparatus itself. For biochemists, that makes the four antioxidant enzymes a sensitive dosimeter of allelochemical pressure; for agronomists, it means the difference between a stimulatory and a lethal application may be narrow and must be measured rather than assumed.

What remains to be seen is whether the same signatures appear under natural soil conditions, where microbial degradation, adsorption and leaching continuously reshape the effective dose of allelochemicals. The authors report that the underlying data are available from the corresponding author upon reasonable request, and they declare no competing interests and no external funding for the work. As a piece of basic plant physiology, however, the study stands on its own: it demonstrates that a common Mediterranean lupin carries leaf chemistry strong enough to flood two tenacious weeds with reactive oxygen species, provoke a costly phenolic counterattack, and ultimately break the enzymatic shield that keeps their metabolism running. In the quiet chemical warfare waged between plants, the lupin has just been shown to hold a formidable arsenal.

Subject of Research: Allelopathic effects of Lupinus termis leaf extract on oxidative stress, antioxidant defenses and metabolism of two weed species

Article Title: Allelopathic influence of Lupinus termis leaf extract on photosynthetic pigments, antioxidants and metabolic activities in Euphorbia helioscopia and Chenopodium murale

Article References: El-Shora, H. M., Tawfik, M. M., El-Hosary, E. G., El-Sayyad, G. S., Elkelish, A., & Abdulhakim, K. N. (2026). Allelopathic influence of Lupinus termis leaf extract on photosynthetic pigments, antioxidants and metabolic activities in Euphorbia helioscopia and Chenopodium murale. Plant Biosystems, 160(4), Article 233. https://doi.org/10.1007/s44473-026-00217-2

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00217-2

Keywords: allelopathy, Lupinus termis, Euphorbia helioscopia, Chenopodium murale, oxidative stress, antioxidant enzymes, reactive oxygen species, malondialdehyde, phenylpropanoid pathway, nitrogen metabolism, bioherbicides, photosynthetic pigments