Selenium biofortification through foliar application has long been recognized as a promising strategy for improving the nutritional quality of staple crops. Unlike soil application, foliar sprays deliver selenium directly to the plant’s photosynthetic tissues, bypassing soil chemistry complications such as pH-dependent availability and microbial immobilization. Yet the integrated effects of foliar selenium on flax productivity, seed nutritional quality, and the molecular mechanisms governing these responses had remained insufficiently characterized—until now.

The researchers tested five different rates of foliar sodium selenite (Na2SeO3) application, ranging from 10 to 90 grams per hectare, alongside a water-sprayed control. What they discovered was strikingly rate-dependent. The 50 grams per hectare treatment, designated T3, produced the highest seed yield in both experimental years, delivering an 8.74 to 9.91 percent increase over the unsprayed control. This yield advantage arose primarily through increased capsule numbers per plant and greater seed counts per capsule—two agronomic traits that directly determine the reproductive output of the flax plant.

Photosynthetic performance told a complementary story. Under T3, flax plants exhibited elevated net photosynthetic rate and increased stomatal conductance, while intercellular CO2 concentration dropped by 24.54 percent. This combination indicates that the selenium-treated plants were consuming CO2 more rapidly through enhanced carbon fixation, drawing down the internal CO2 pool even as their stomata opened wider to admit more atmospheric carbon. The result is a more efficient photosynthetic engine, capable of channeling greater assimilate into developing seeds.

Beyond photosynthesis, the 50 grams per hectare treatment also produced the most favorable antioxidant profile in the seeds. Superoxide dismutase activity—the first line of enzymatic defense against reactive oxygen species—reached its highest level under T3, while malondialdehyde content, a widely used biomarker of lipid peroxidation and oxidative membrane damage, fell to its lowest. This dual pattern suggests that moderate selenium application primes the seed’s redox defense system without triggering the oxidative stress that higher selenium doses might induce.

Seed selenium content increased in a dose-dependent manner across all treatments, peaking under the 90 grams per hectare treatment at 21.96-fold that of the control. However, the 50 grams per hectare treatment achieved a 15.60-fold increase while simultaneously improving fatty acid quality: linoleic acid content rose by 18.51 percent and linolenic acid content by 4.85 percent. These two essential fatty acids, which humans cannot synthesize and must obtain from dietary sources, are the principal nutritional reasons flax oil commands premium market value.

To understand the molecular machinery underlying these physiological changes, the team performed RNA sequencing on seeds from the control and T3 treatments. The analysis identified 5,203 differentially expressed genes—2,523 upregulated and 2,680 downregulated—spanning a remarkable breadth of biological processes. Functional enrichment analysis revealed major clusters in photosynthesis and carbon metabolism, redox-related processes, selenium-associated metabolism, and lipid and fatty-acid metabolism. The scale of the transcriptional response underscores that foliar selenium is not a narrow nutritional intervention but a systemic signal that reprograms seed development at multiple levels.

Complementing the transcriptomic data, a 4D label-free proteomic analysis identified 76 differentially expressed proteins, comprising 23 upregulated and 53 downregulated proteins. These proteins clustered around antioxidant and detoxification responses, photosynthesis and energy metabolism, and lipid metabolism. Notably, the integration of transcriptomic and proteomic datasets revealed limited overlap between the two molecular layers: only eight gene-protein pairs showed significant alteration at both the transcript and protein levels. This limited concordance is a well-known feature of plant molecular biology, reflecting the complex post-transcriptional and post-translational regulation that separates messenger RNA abundance from actual protein accumulation.

The eight concordant gene-protein pairs included proteins involved in late embryogenesis abundant (LEA) responses, pathogenesis-related protein 5, and plastid lipid-associated proteins—molecules that collectively point to enhanced seed maturation, defense priming, and lipid body organization under moderate selenium treatment. Their dual-level confirmation provides the strongest molecular evidence in the study that selenium application genuinely rewires seed biology rather than merely altering gene expression patterns that never materialize as protein changes.

The findings carry practical significance for agricultural systems seeking to combat selenium deficiency through crop biofortification. By identifying 50 grams per hectare as the optimal rate—the treatment that maximizes yield, antioxidant status, and fatty acid quality simultaneously—the study offers a rational basis for optimizing foliar sodium selenite application in flax production. At the same time, the integrated multi-omics framework demonstrates that the molecular response to foliar selenium encompasses carbon metabolism, redox regulation, selenium-associated metabolism, lipid metabolism, and seed development, providing a mechanistic foundation that could guide biofortification strategies in other oilseed crops as well.

Subject of Research: Plant Molecular Biology

Article Title: Transcriptomic, proteomic, and physiological comparative analyses of foliar selenium application in flax

Article References: Transcriptomic, proteomic, and physiological comparative analyses of foliar selenium application in flax. (n.d.). https://doi.org/10.1186/s12870-026-10099-3

Image Credits: AI Generated

DOI: 10.1186/s12870-026-10099-3

Keywords: selenium biofortification, flax, foliar application, transcriptomics, proteomics, fatty acids, antioxidant, seed yield, BMC Plant Biology, plant physiology, Transcriptomic, proteomic