Alkaline stress is far more than salt stress with a higher pH, the review’s authors from institutions including the Chinese Academy of Sciences, Northeast Forestry University, Texas Tech University, and the University of Otago emphasize. Neutral salt stress, typically caused by sodium chloride or sodium sulfate, damages plants mainly through ion toxicity and osmotic disruption without greatly altering soil pH. Alkaline stress adds an entirely different layer of injury: bicarbonate and carbonate ions actively strip protons from the root environment, collapse the proton gradients plants depend on to feed themselves, and precipitate essential nutrients such as calcium, magnesium, iron, and manganese into insoluble forms. The result is a quadruple threat combining osmotic stress, sodium toxicity, high-pH injury, and severe nutrient starvation. Bicarbonate also interferes with ion transport, weakens membrane stability, and disturbs intracellular pH regulation, making alkaline stress substantially more complex and damaging than neutral salt stress alone.

The frontline of plant defense, the review finds, is a family of molecular machinery called proton pumps. Plasma membrane H⁺-ATPases use ATP hydrolysis to pump hydrogen ions out of root cells, building an electrochemical gradient that powers nutrient uptake and drives sodium expulsion through the Salt Overly Sensitive 1 transporter. This continuous proton extrusion also acidifies the rhizosphere, partially counteracting the alkaline soil itself. Studies of the alkaline-tolerant grass Puccinellia tenuiflora, a halophyte that thrives on sodium carbonate soils, show that sodium carbonate treatment increases both the expression and the activity of plasma membrane and vacuolar proton pumps alongside vacuolar Na⁺/H⁺ exchangers, which use the proton gradient to sequester sodium inside vacuoles while stabilizing cytosolic pH. Genetic engineering of these proton pump components has already improved alkaline performance in crops: expressing a vacuolar H⁺-ATPase subunit from the salt marsh grass Spartina alterniflora in rice enhanced salt tolerance, and a vacuolar H⁺-pyrophosphatase from Zoysia matrella improved salt tolerance when introduced into Arabidopsis.

Equally remarkable is the strategy of organic acid secretion. In Puccinellia tenuiflora, alkaline treatment triggers a surge of citrate and malate released into the rhizosphere, shifting soil pH from strongly alkaline toward near-neutral. Metabolomic and proteomic analyses reveal that this is no passive byproduct accumulation: the plant actively reroutes carbon metabolism, upregulating the tricarboxylic acid cycle, glyoxylate metabolism, and glycolysis, and increasing the abundance of dehydrogenases and synthases devoted to organic acid production. Once secreted, citrate and malate partially dissociate, releasing protons that neutralize alkalinity and form carbonic acid that decomposes into carbon dioxide and water. Their carboxyl groups also chelate iron and manganese, unlocking these micronutrients from the insoluble grip of high-pH soils, while released organic anions help maintain membrane charge balance. Comparable responses have been documented in barley, alfalfa, Leymus chinensis, Yorkshire fog, and red clover, with alkaline salt treatments consistently inducing stronger organic acid accumulation than neutral salt treatments, and increased organic acid content correlating with root growth recovery and reduced sodium-to-potassium ratios.

Inside the cell, tolerant plants wage a coordinated battle over ion balance. Halophytes exploit sodium salts themselves as osmoticum, storing them harmlessly in vacuoles while keeping cytosolic sodium low and preserving potassium. This dual strategy of vacuolar sequestration and potassium retention protects metabolism while maintaining turgor pressure. Yet alkaline stress threatens potassium homeostasis directly: membrane depolarization and reactive oxygen species can activate outward-rectifying potassium channels, causing damaging potassium leakage. The review highlights that halophytes counter this by rapidly enhancing plasma membrane H⁺-ATPase activity, which repolarizes the membrane, suppresses potassium efflux, and sustains the driving force for high-affinity potassium uptake. Under both salt and alkaline stresses, halophytes maintain far higher cytosolic potassium-to-sodium ratios than sensitive glycophytes, evidence of tighter coordination among proton pumps, potassium transport, and sodium-hydrogen exchange.

The antioxidant dimension of alkaline tolerance is equally sophisticated. Osmotic stress and ion toxicity drive excess production of reactive oxygen species, which, if unchecked, oxidize lipids, proteins, and DNA. High apoplastic pH and iron deficiency compound the problem by further promoting ROS formation. Halophytes such as Atriplex, Suaeda, and the extremophile model Eutrema salsugineum maintain higher baseline activities of superoxide dismutase, catalase, and peroxidases, and induce these enzymes more rapidly than glycophytes, showing correspondingly less lipid peroxidation under alkaline conditions. Beyond the enzymatic cascade, which converts superoxide to hydrogen peroxide and then to water, non-enzymatic antioxidants including ascorbate and glutathione form the ascorbate-glutathione cycle, a major route for hydrogen peroxide detoxification in chloroplasts and the cytosol. Halophytes retain higher glutathione contents and glutathione-to-oxidized-glutathione ratios than glycophytes, while accumulating phenolics and flavonoids that scavenge ROS through hydrogen atom donation and metal chelation.

The review also brings the rhizosphere microbiome into the tolerance equation. Plant growth-promoting rhizobacteria isolated from saline-alkali soils secrete organic acids and extracellular polysaccharides that lower rhizosphere pH, dissolve calcium carbonate, and improve iron and phosphate availability. These bacteria also produce phytohormones and ACC deaminase, an enzyme that reduces stress-induced ethylene accumulation and reshapes root architecture. High-throughput sequencing of halophyte rhizospheres in Salicornia europaea, Suaeda salsa, and Atriplex species shows microbial communities distinct from adjacent bulk soil, enriched in functions for polysaccharide synthesis, osmotic adjustment, and antioxidant activity. Arbuscular mycorrhizal fungi add another layer, extending the effective absorptive surface of roots and alleviating growth inhibition under alkaline stress in Leymus chinensis seedlings and poplar, improving osmotic regulation and ion balance.

At the molecular level, the review catalogues a growing arsenal of regulatory genes. Early alkalinity perception likely involves extracellular pH sensing through peptide-receptor complexes such as RGF1-RGFR and Pep1-PEPR, although no dedicated bicarbonate receptor has yet been identified, and whether these receptors act under actual alkaline stress remains an open question. Downstream, calcium signals activate the SOS pathway, while regulators such as PKS5, the calcium sensor SCaBP3, the wheat proteins TaCCD1 and TaSAUR215, and the tomato 14-3-3 protein TFT4 fine-tune proton pump activity under high pH. Striking examples of breeding-relevant natural variation have emerged: the AT1/GS3 locus, encoding an atypical G-protein gamma subunit, modulates hydrogen peroxide distribution across root membranes and its modification improves alkaline tolerance in sorghum, rice, maize, and wheat. In maize, natural variation in the EF-hand calcium-binding protein ZmNSA1 reduces shoot sodium accumulation, while tomato lost saline-alkaline tolerance during domestication through weakened expression of SlSCaBP8, a defect an introgression line carrying the wild promoter haplotype reverses. Transcription factor networks involving NAC, HD-Zip, AP2/ERF, bZIP, TIFY/JAZ, MYB, and bHLH families coordinate hormone signaling, redox balance, iron acquisition, and root development, with genes such as GsERF71 enhancing proton pumping and grapevine VvERF1B stimulating organic acid exudation.

The authors argue that translating these mechanisms into crops will require moving beyond descriptive studies toward prioritized, testable hypotheses connecting sensing, rhizosphere regulation, molecular control, and field performance. They propose cell-type-resolved imaging of pH, calcium, and ROS signals, comparative omics under matched salt and alkaline treatments, synthetic microbial communities, and genome editing approaches including promoter editing and allele stacking. Durable tolerance, they conclude, will come from combining early pH sensing, proton extrusion, sodium compartmentation, nutrient acquisition, ROS buffering, and root remodeling, validated under realistic field conditions where salts, high pH, nutrient limitation, and drought collide. With agriculture worldwide facing expanding saline-alkali soils and rising food demand, the plants that already survive these extremes may hold the genetic blueprints for feeding the future.

Subject of Research: Physiological and molecular mechanisms of plant tolerance to bicarbonate-induced alkaline soil stress

Article Title: Physiological and molecular processes of plant tolerance to bicarbonate-induced alkaline stress

Article References: Fu, J., Li, L., Xing, M., Xie, W., Zhu, C., Yang, K., Nie, X., Yin, X., Mostofa, M. G., Burritt, D., Tran, L.-S. P., Bu, Y., & Li, W. (2026). Physiological and molecular processes of plant tolerance to bicarbonate-induced alkaline stress. Stress Biology, 6(1), Article 53. https://doi.org/10.1007/s44154-026-00325-1

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00325-1

Keywords: alkaline stress, bicarbonate, halophytes, proton pumps, organic acid secretion, ion homeostasis, reactive oxygen species, rhizosphere microbiome, transcription factors, saline-alkali agriculture, crop breeding, soil pH

Halophytes occupy one of the most punishing niches in the plant world. Rooted in soils saturated with salt and repeatedly exposed to tidal flooding, intense sunlight and oxidative stress, they must defend themselves with an unusually robust chemical arsenal. That stress-driven metabolism often leads to elevated production of phenolics, flavonoids, tannins and other secondary metabolites, many of which have documented antioxidant, anti-inflammatory and even anticancer properties when tested in laboratory systems. Plants that manufacture these compounds to survive are, in effect, pre-formulating drugs, and the Bharathidasan team set out to quantify exactly how much pharmacological value two representative species carry.

The researchers collected both plants from the Cuddalore coast region of Tamil Nadu and prepared a series of solvent extracts, ranging from non-polar hexane to more polar ethyl acetate and other fractions. Sequential extraction with solvents of increasing polarity is a standard strategy in natural products chemistry because different classes of compounds partition differently: non-polar solvents pull out lipids, terpenoids and certain phenolic derivatives, while more polar solvents recover flavonoid glycosides, tannins and free amino acids. By comparing the same plant across solvents, the team could pinpoint which fraction carried which activity, a critical step for anyone hoping to isolate a single therapeutic molecule later.

The chemical inventory was striking. The ethyl acetate extract of Suaeda maritima recorded the highest total flavonoid content at 272.74 milligrams of quercetin equivalents per gram, alongside 114.32 milligrams of gallic acid equivalents per gram of total phenolics, 95.68 milligrams of tannic acid equivalents per gram of tannins, and 122.43 milligrams of leucine equivalents per gram of free amino acids. These are substantial concentrations for a wild-harvested marsh plant. Flavonoids and phenolic acids are the classical workhorses of plant antioxidant chemistry, capable of donating electrons or hydrogen atoms to neutralise reactive oxygen species, the unstable molecules implicated in inflammation, cardiovascular disease, neurodegeneration and cancer progression.

Bioactivity testing told an equally interesting story, but with a twist in which plant came out ahead. The hexane extract of Sesuvium portulacastrum delivered the strongest radical-scavenging performance in the DPPH assay, with an IC50 value of 63.32 micrograms per millilitre, meaning the concentration needed to neutralise half of the synthetic free radicals in the test. The same hexane fraction also dominated the anti-inflammatory battery of tests: it inhibited heat-induced denaturation of bovine serum albumin with an IC50 of 68.18 micrograms per millilitre, suppressed proteinase activity with an IC50 of 66.21 micrograms per millilitre, and scavenged nitric oxide with an IC50 of 58.65 micrograms per millilitre. Protein denaturation is a hallmark of inflammatory states, and compounds that stabilise protein structure or block proteolytic enzymes are considered useful templates for anti-inflammatory drug development. Nitric oxide, while a vital signalling molecule at physiological levels, becomes a damaging inflammatory mediator when overproduced, so nitric oxide scavenging is another clinically relevant benchmark.

The observation that non-polar hexane fractions produced the strongest functional effects, while polar ethyl acetate fractions carried the highest measured phytochemical content, illustrates a recurring lesson in pharmacognosy: quantity of known marker compounds does not always predict biological potency. Hexane-soluble constituents such as fatty acid derivatives, terpenoids and certain lipophilic phenolics can be disproportionately active even when classical colorimetric assays register their presence weakly. Identifying which specific molecules drive the activity requires chemical characterisation at the compound level, and this is where the team turned to instrumental analysis.

Gas chromatography coupled with mass spectrometry, or GC–MS, was used to profile the volatile and semi-volatile constituents of the extracts, revealing a suite of major bioactive compounds characteristic of halophyte chemistry. To prioritise candidates for drug development, the researchers then turned to molecular docking, a computational technique that predicts how tightly a small molecule fits into the binding pocket of a disease-relevant protein. Two inflammatory protein structures, deposited in the Protein Data Bank under the identifiers 1IK3 and 5IKR, served as the molecular targets. Among the identified phytochemicals, 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione showed the strongest binding affinities, at minus 7.1 and minus 7.0 kilocalories per mole for the two targets respectively. Binding energies in this range suggest meaningful intermolecular contacts such as hydrogen bonding and hydrophobic packing, which in docking studies are typically taken as an encouraging, though preliminary, sign of inhibitory potential.

The team also ran the lead compounds through SwissADME, a widely used web platform that estimates whether a molecule behaves like a plausible oral drug. The analysis indicated favourable drug-like properties, including profiles consistent with reasonable absorption, distribution and metabolic behaviour under the standard Lipinski-style criteria used in early drug discovery. No docking study or ADME prediction can replace experimental pharmacology, but together they act as a molecular sieve, filtering dozens of crude extract constituents down to a shortlist of compounds worth the expense of isolation, synthesis and biological testing.

The authors are careful to frame the work as an early-stage screening effort rather than a therapeutic claim. All of the antioxidant and anti-inflammatory data come from in vitro assays, and the docking results are computational predictions; the study itself concludes that the halophytes, particularly their hexane extracts, warrant further in vitro and in vivo investigation. That pipeline matters: many plant extracts that shine in a test tube fail when confronted with living systems, where issues of bioavailability, metabolism, toxicity and target specificity intervene. Nevertheless, the convergence of strong assay results, identifiable bioactive compounds, encouraging docking scores and favourable drug-likeness predictions is exactly the combination that natural products chemists look for when deciding which species to pursue.

Beyond the laboratory, the study carries an ecological and economic message. Coastal salt marshes are often treated as wastelands, reclaimed for aquaculture, industry or development, yet they harbour species with demonstrated pharmaceutical value and play vital roles in shoreline protection and nutrient cycling. Work of this kind strengthens the case for conserving these habitats, both for their ecosystem services and as living libraries of chemical diversity. If subsequent animal studies and, eventually, clinical research confirm the promise suggested by the Cuddalore samples, the humble marsh plants swaying at the edge of the Bay of Bengal may find a second career as sources of next-generation anti-inflammatory medicines.

Subject of Research: Antioxidant and anti-inflammatory bioactive compounds in coastal halophyte plants

Article Title: Assessment of antioxidant and anti-inflammatory effects of Suaeda maritima and Sesuvium portulacastrum collected from Cuddalore coast region

Article References: Baskaran, G., Natesan, M., Palanisamy, B. M., Mathiyazhagan, S., & Raji, S. (2026). Assessment of antioxidant and anti-inflammatory effects of Suaeda maritima and Sesuvium portulacastrum collected from Cuddalore coast region. Plant Biosystems, 160(5), Article 254. https://doi.org/10.1007/s44473-026-00266-7

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00266-7

Keywords: halophytes, Suaeda maritima, Sesuvium portulacastrum, antioxidant activity, anti-inflammatory, phytochemistry, molecular docking, GC-MS, SwissADME, salt marsh, natural products, Cuddalore coast