Chitosan–Selenium Spray Helps Wheat Seedlings Weather Salty Irrigation Water

Salt is quietly strangling one of the world’s most important staple crops. As irrigation water grows increasingly saline in arid farming regions, wheat seedlings face a double assault: the sodium chloride disrupts their water balance and poisons their cells, while reactive oxygen species tear through membranes and pigments. Now, a team of researchers at the HUN-REN Centre for Agricultural Research in Martonvásár, Hungary, working with colleagues at Tarim University in China, reports that a simple foliar spray combining two well-known biostimulants—chitosan and selenium—can measurably improve wheat seedling growth under salt stress. The study, published in BMC Plant Biology, offers a technically detailed look at how the formulation behaves on the leaf surface and which stress-response genes it switches on.

The choice of wheat as the experimental subject reflects both its global importance and its well-documented sensitivity to salinity during early development. Wheat is among the most widely cultivated cereals on Earth, and in many irrigated production systems—particularly in arid and semi-arid regions of Central and Western Asia, North Africa, and Australia—the water available to farmers carries substantial dissolved salt loads. Seedling establishment is a particularly vulnerable window, because young plants have limited root systems, thin cuticles, and immature antioxidant machinery. A seedling that survives early salt exposure with reduced vigor often carries that penalty through to tillering and grain fill, which is why interventions aimed specifically at the seedling stage can have disproportionate agronomic value even when the plants eventually recover.

The two cultivars examined in the study, Chamran and Mehregan, are bread wheat varieties bred for the contrasting but overlapping challenges of Iranian and regional production environments. Including two genotypes rather than one matters scientifically because salt responses in wheat are strongly genotype-dependent: varieties differ in their capacity to exclude sodium at the root, to compartmentalize it in vacuoles, and to maintain photosynthetic activity under osmotic strain. When a treatment effect appears in both cultivars, as the fresh-weight benefit of the combined formulation did at every salinity level tested, it suggests a mechanism that operates broadly rather than one contingent on a particular genetic background. At the same time, the magnitude of the benefit differed between the two lines, with Mehregan showing a larger relative gain at the highest salt concentration, a reminder that biostimulant performance cannot be assumed to transfer uniformly across germplasm.

The severity of the salt treatments deserves attention when interpreting the results. Irrigating with 150 millimolar sodium chloride already imposes stress well beyond what most productive wheat fields experience; 300 millimolar approaches the limits of what wheat seedlings can tolerate at all. These concentrations were chosen to create a steep stress gradient in which protective effects could be detected unambiguously, not to mimic field conditions directly. The fact that plant height, fresh weight, and dry weight all declined substantially at the highest concentration in both cultivars confirms that the stress was genuinely severe. Against that backdrop, even modest absolute differences in biomass between sprayed and unsprayed plants represent meaningful biological protection, and the roughly thirty-five percent fresh-weight advantage of the combined treatment over the unsprayed control in Chamran at 300 millimolar sodium chloride is notable.

Chitosan itself has a long history as a plant-protective agent, and its mechanism of action is worth unpacking. Derived by deacetylation of chitin from crustacean shells or fungal cell walls, chitosan is a positively charged polysaccharide that can interact with negatively charged components of plant cell surfaces. It is recognized by plants as a microbe-associated molecular pattern, triggering innate immune signaling pathways that overlap with those activated during abiotic stress. Spraying chitosan on leaves has been reported to induce stomatal closure, stimulate the phenylpropanoid pathway, and prime antioxidant enzymes, effects that collectively harden plants against subsequent stress. The polymer also forms films, which is why it is used commercially as an edible coating for fruit; on a leaf, that film-forming behavior may both retain moisture and slow the diffusion of dissolved solutes.

Selenium occupies an unusual position in plant biology. It is not considered an essential element for higher plants, yet at low concentrations it reliably alleviates oxidative stress in many species. The reason lies in its chemistry: selenite taken up by leaf tissue can be assimilated into selenocysteine and ultimately into selenium-containing forms that bolster the glutathione peroxidase system, an alternative route for decomposing lipid peroxides that complements the ascorbate-glutathione cycle. Selenium supplementation has also been shown to enhance the activity of catalase and superoxide dismutase and to slow chlorophyll degradation under stress. The dose window is narrow, however, because selenium becomes toxic to plants at concentrations only modestly above those that are beneficial, which makes delivery method and formulation critical variables in any field application.

The formulation strategy used in the study—ionotropic gelation with tripolyphosphate—is a standard technique for assembling chitosan into small cross-linked particles. When a tripolyphosphate solution is added to an acidic chitosan solution, the multivalent anion bridges the cationic polymer chains, condensing them into discrete nanoparticles. Incorporating sodium selenite into this process entraps or associates the selenium species within the particle matrix rather than leaving it as a free salt on the leaf surface. The practical rationale is that a particle-associated active ingredient may adhere better to the waxy cuticle, release its payload more gradually, and suffer less from rapid wash-off or photodegradation than a simple aqueous spray. The authors were careful, however, to note that the physicochemical properties of their specific formulation—particle size, surface charge, selenium loading efficiency, and release kinetics—were not characterized in this work, leaving an important gap between the concept and a fully validated delivery system.

The confocal microscopy experiment using fluorescein isothiocyanate-labeled chitosan provides some of the most visually direct evidence in the paper. Fluorescence was strongest in the epidermal layer and weaker in the underlying mesophyll, indicating that the polymer associates readily with the outer leaf tissues but penetrates only partially into the interior. This pattern is consistent with what is known about foliar uptake in general: the cuticle is a formidable hydrophobic barrier, and most solutes enter through stomata, trichomes, or specialized epidermal cells rather than diffusing across the cutin matrix. The authors are appropriately cautious in their interpretation, emphasizing that detecting the labeled chitosan demonstrates association with the leaf but does not prove that selenium, or the intact formulation, was internalized. Tracking the selenium itself would require a different analytical approach, such as isotope labeling or elemental imaging.

The gene expression data add a molecular dimension to the physiological observations. The genes examined span several functional categories that map directly onto the known components of salt stress. TaAPX and TaCAT encode ascorbate peroxidase and catalase, the two central enzymes of hydrogen peroxide detoxification. TaNHX1 encodes a vacuolar sodium-proton antiporter that sequesters sodium ions inside vacuoles, removing them from the cytoplasm where they would interfere with enzymatic function. TaHKT9-7D belongs to the high-affinity potassium transporter family, whose members participate in sodium retrieval and potassium-sodium balance in both roots and leaves. TaP5CS catalyzes the rate-limiting step in proline biosynthesis, and Ta4CL3-6B encodes a 4-coumarate ligase acting early in the phenylpropanoid pathway, which supplies lignin precursors and a wide range of protective secondary metabolites. TaPXPAO is involved in polyamine catabolism, a process that both generates hydrogen peroxide and participates in stress signaling.

The pattern of expression changes tells a coherent story. In unsprayed plants, salt exposure actually decreased the transcript levels of most of these genes, a somewhat counterintuitive result that may reflect stress-imposed suppression of transcription or a failure of the seedlings to mount a full defensive response at the severe concentrations used. The single gene that rose, TaP5CS, aligns with the accumulation of proline, the classic osmoprotectant whose synthesis plants upregulate under water stress. In contrast, the selenium-containing treatments at the highest salt level elevated TaCAT, TaNHX1, and Ta4CL3-6B in both cultivars, suggesting activation of antioxidant defense, sodium compartmentalization, and phenylpropanoid metabolism respectively. The combined formulation additionally influenced the polyamine catabolism gene, hinting at a broader reprogramming of stress metabolism when the two biostimulants act together.

The authors are explicit that these expression changes are correlative: no enzyme activities, metabolite quantities, or ion contents were measured to confirm that the transcriptional shifts translated into functional differences. This is a standard and honest limitation of RT-qPCR surveys, and it defines the agenda for follow-up work. Measuring catalase activity, tissue sodium and potassium concentrations, proline levels alongside TaP5CS expression, and phenylpropanoid end products would connect the molecular signals to the growth outcomes. Similarly, the weak correlation between growth traits and pigment contents, with correlation coefficients not exceeding 0.30, indicates that the fresh-weight benefit of the treatment cannot be explained simply by preserved chlorophyll; other processes, such as osmotic adjustment, membrane stability, or ion homeostasis, are likely contributing.

The proline data illustrate this point nicely. Proline rose with increasing salinity in the selenium-treated and combined-treatment plants, consistent with induced TaP5CS expression, and proline serves multiple roles beyond osmotic adjustment: it scavenges reactive oxygen species directly, stabilizes proteins and membranes, and buffers cellular redox state. A treatment that enhances proline accumulation under salt stress therefore plausibly contributes to the observed biomass protection through mechanisms invisible to chlorophyll measurements. Disentangling how much of the growth benefit flows through osmotic protection versus antioxidant reinforcement versus ion management will require the kind of integrative physiological follow-up the authors themselves call for.

From an applied perspective, the study sits within a growing literature on biostimulants as complements to conventional breeding and soil management for salinity adaptation. Breeding for salt tolerance in wheat has proven slow because tolerance is controlled by many genes of modest effect and is strongly environment-dependent. Foliar interventions offer a complementary route: they can be applied reactively when salinity is known to be a problem, combined with existing agronomic practice, and adjusted by dose and timing. The caveats the authors raise—uncharacterized formulation physics, seedling-stage results only, controlled-environment conditions, and no field validation—are the standard hurdles between a promising greenhouse result and a usable product, and their candor about them strengthens rather than weakens the study’s contribution. The work was supported by Hungarian national research funding through the Thematic Excellence Program and the NRDI Fund, and the article is published open access under a Creative Commons license, making the full dataset and methods available to any research group wishing to build on these findings.

Subject of Research: Foliar chitosan–selenite biostimulant effects on wheat seedlings under salt stress

Article Title: Foliar chitosan–selenite formulation improves wheat seedling growth under NaCl irrigation

Article References: Gholizadeh, F., Fábián, A., Sohail, H., Majláth, I., & Janda, T. (2026). Foliar chitosan–selenite formulation improves wheat seedling growth under NaCl irrigation. BMC Plant Biology. https://doi.org/10.1186/s12870-026-10095-7

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10095-7

Keywords: wheat, salinity stress, chitosan, selenium, foliar application, biostimulants, gene expression, antioxidant defense, proline, confocal microscopy, plant physiology, NaCl