The study, published in Plant Cell Reports, combined physiology, transcriptomics, metabolomics, and enzyme assays to trace exactly how exogenous trehalose bolsters salt tolerance in tomato seedlings. The findings reveal that hydrogen sulfide acts as a central mediator in trehalose-induced protection, and that the downstream response funnels through two metabolic routes: the phenylpropanoid pathway, a workhorse of plant defense chemistry, and the less celebrated cyanoamino acid metabolism pathway, which processes cyanogenic compounds. The work offers a clearer mechanistic picture of how two stress-protective agents interact, and it hints at practical strategies for shielding crops from salinity.

Trehalose is no stranger to stress biology. This disaccharide, composed of two glucose units, accumulates in an astonishing range of organisms, from resurrection plants that survive near-total desiccation to yeast cells braving heat and dehydration. In plants, trehalose and its phosphorylated precursor trehalose-6-phosphate serve dual roles as osmoprotectants that stabilize proteins and membranes, and as sugar signals that rewire metabolism during stress. Previous studies had shown that spraying tomato seedlings with trehalose improves their performance under salt stress by modulating reactive oxygen species, photosynthesis, and osmolyte synthesis. Hydrogen sulfide, meanwhile, has shed its reputation as merely a toxic, rotten-egg-smelling gas. Over the past two decades, plant biologists have established that H2S functions as a genuine signaling molecule, regulating seed germination, stomatal closure, and a broad spectrum of abiotic stress responses, often through persulfidation, a chemical modification that alters the activity of target proteins.

What remained unknown was how these two protective agents relate to each other when deployed together. The Guangxi team, led by corresponding author Changxia Li with co-first authors Jin Qi and Zhang Zhang, designed a series of experiments to answer that question. They grew tomato seedlings under salt stress and treated them with trehalose alone, with sodium hydrosulfide (NaHS), a donor of hydrogen sulfide, alone, or with both compounds simultaneously. The physiological results were striking: both treatments significantly alleviated salt-induced growth inhibition, but the combined treatment produced the most pronounced protective effect, suggesting the two agents act in complementary or synergistic ways.

To dissect the direction of the relationship, the researchers turned to pharmacology. They applied validamycin A, an inhibitor of trehalose biosynthesis, and hypotaurine, a chemical scavenger that mops up hydrogen sulfide. The logic was simple but powerful: if removing hydrogen sulfide abolishes trehalose’s benefits, then trehalose must depend on the gas to work. The experiments delivered a clear verdict. The protective effect of trehalose was largely dependent on hydrogen sulfide, because scavenging the gas with hypotaurine substantially undermined trehalose-induced salt tolerance. In contrast, the efficacy of the NaHS donor was independent of trehalose, indicating a one-directional dependency: trehalose needs hydrogen sulfide, but hydrogen sulfide does not need trehalose. The authors are careful to note the limits of this interpretation. Their data mainly support a requirement for H2S in trehalose action rather than demonstrating that hydrogen sulfide alone is sufficient to reproduce the full trehalose response, and they call for further functional analyses to clarify the precise hierarchy between the two signals.

With the physiological dependency established, the team moved to the molecular level using RNA sequencing. The transcriptomic analysis showed that trehalose modulates the salt stress response of tomato seedlings at the transcriptional level via hydrogen sulfide, and it pinpointed phenylalanine biosynthesis as a core metabolic target. Phenylalanine is the gateway amino acid for the phenylpropanoid pathway, one of the most important specialized metabolic networks in plants. From phenylalanine, plants build an enormous arsenal of compounds, including lignin, which reinforces cell walls and forms apoplastic barriers against ion intrusion; flavonoids and anthocyanins, which act as antioxidants; and a variety of phenolic compounds that buffer oxidative damage. The second pathway flagged by the analysis was cyanoamino acid metabolism, the route that produces and processes cyanogenic glycosides, nitrogen-containing defense metabolites derived from amino acids.

The metabolomic data reinforced the transcriptomic picture. Compared with seedlings receiving salt plus trehalose, those that also received the hydrogen sulfide scavenger hypotaurine showed significantly reversed accumulation of protective metabolites. In the phenylpropanoid pathway, the compounds p-coumaryl alcohol and coniferyl alcohol, both monolignols that feed into lignin biosynthesis, accumulated in response to trehalose but dropped back when hydrogen sulfide was removed. In the cyanoamino acid pathway, the cyanogenic glycosides amygdalin and prunasin, compounds more famous for their roles in almond and stone fruit bitterness, followed the same pattern. This is a notable finding because it implicates a pathway usually discussed in the context of herbivore defense in abiotic stress tolerance, adding to a growing body of evidence that cyanogenic metabolism contributes to how plants cope with environmental challenges.

The enzymatic and gene expression data tied the whole story together. The salt plus trehalose treatment significantly elevated the activities of key enzymes in the phenylpropanoid biosynthesis pathway, including 4-coumarate-CoA ligase (4CL), caffeoyl-CoA O-methyltransferase (CCoAOMT), and peroxidase (POD), as well as enzymes in the cyanoamino acid metabolism pathway, namely mandelonitrile lyase (MDL) and beta-glucosidase (bglX). Consistent with these biochemical changes, the transcript levels of the corresponding encoding genes, including 4CL1, CCoAOMT, POD9, POD43, MDL3, and bglX1, were significantly upregulated. When hypotaurine was added to scavenge hydrogen sulfide, the trehalose-induced enhancement of both enzyme activities and gene expression was significantly reversed. At the molecular level, this confirms that hydrogen sulfide sits upstream of these metabolic changes, serving as a central mediator through which trehalose exerts its protective influence during salt stress.

Why does this matter beyond the laboratory? Salinity stress imposes a double burden on plants: excess sodium ions are toxic, and the osmotic stress they create makes it harder for roots to take up water. Plants respond with a suite of defenses, including osmolyte accumulation, ion homeostasis, and antioxidant systems that neutralize the reactive oxygen species generated under stress. The phenylpropanoid pathway sits at the heart of several of these defenses, supplying lignin for physical barriers and phenolic compounds for antioxidant protection. If trehalose triggers these defenses only through hydrogen sulfide, then breeding or engineering approaches might target the signaling relay itself, for instance by enhancing H2S production capacity or persulfidation of key regulatory proteins, to amplify a crop’s intrinsic stress response. Alternatively, combined field treatments of trehalose and hydrogen sulfide donors could be optimized to exploit the synergy observed in seedlings, though translating greenhouse pharmacology to open-field agriculture always demands careful validation.

The study also enriches a rapidly expanding literature on hydrogen sulfide as a master regulator of plant stress resilience. Recent work has shown that H2S promotes lateral root formation in peach through persulfidation of the SnRK1α kinase, balances hydrogen sulfide and hydrogen cyanide homeostasis in Arabidopsis under osmotic stress, and modulates phenolic metabolism to alleviate salt stress in tomato. The Guangxi findings slot neatly into this picture while adding a new layer: they position trehalose, a sugar signal, upstream of the gas, and they extend the downstream reach of the gas into cyanoamino acid metabolism, a pathway rarely invoked in salt tolerance research. The authors acknowledge that much remains to be resolved, particularly whether hydrogen sulfide alone can reproduce the complete trehalose response and what the precise hierarchical relationship between the two signals looks like under field conditions. But the core message is already compelling: in salt-stressed tomato seedlings, a protective sugar whispers its instructions through a stinky gas, and the plant listens by building stronger walls and richer chemistry. For a crop that feeds billions and a planet whose farmland grows saltier by the season, that conversation is worth every effort to understand and, ultimately, to harness.

Subject of Research: Hydrogen sulfide-dependent trehalose signaling that enhances salt tolerance in tomato seedlings through phenylpropanoid and cyanoamino acid metabolism

Article Title: H2S-dependent trehalose-induced salt tolerance in tomato involves phenylpropanoid and cyanoamino acid pathways

Article References: Qi, J., Zhang, Z., Li, S., Su, J., Tian, Y., Yu, W., & Li, C. (2026). H2S-dependent trehalose-induced salt tolerance in tomato involves phenylpropanoid and cyanoamino acid pathways. Plant Cell Reports, 45(10), Article 283. https://doi.org/10.1007/s00299-026-03969-5

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03969-5

Keywords: trehalose, hydrogen sulfide, salt stress, tomato, phenylpropanoid pathway, cyanoamino acid metabolism, transcriptomics, plant stress signaling, sodium hydrosulfide, hypotaurine, antioxidant defense, Plant Cell Reports

Soil salinity is one of the most damaging abiotic stresses in agriculture. When sodium and chloride ions accumulate in the root zone, plants struggle to take up water, essential nutrients become imbalanced, and toxic sodium builds up inside tissues. For okra, a warm-season vegetable prized for its edible pods and its growing reputation as a nutraceutical food, salinity is particularly harmful at the earliest stages of life. Salt strongly suppresses seed germination and stunts seedling growth, which means that even modestly saline fields can translate into poor stands and reduced yields. Earlier work from the same research group had shown that molecules such as methyl jasmonate and melatonin can bolster okra’s salt tolerance, but the upstream role of gaseous signals, and specifically how hydrogen sulfide interacts with abscisic acid signaling, remained poorly understood.

To close that gap, the team designed a two-tier experimental program. In germination assays, okra seeds were challenged with 100 millimolar sodium chloride in hydroponic culture, while longer-term pot experiments subjected seedlings to a harsher 150 millimolar salt regime. Across both systems, the researchers applied NaHS at gradient concentrations of 10, 50, 100 and 500 micromolar, allowing them to identify the dose that offered the greatest protection. Crucially, they also included a validation treatment combining 100 micromolar NaHS with 1 millimolar hypotaurine, a well-established scavenger of hydrogen sulfide. If hypotaurine wiped out the protective effect, it would demonstrate that the benefit depended specifically on hydrogen sulfide rather than on some unrelated chemical property of the donor compound.

The results were striking. Salt stress alone slashed germination rates and seedling biomass, but among the tested concentrations, 100 micromolar NaHS proved optimal, substantially rescuing growth. When hypotaurine was added alongside NaHS, most of that protection vanished, confirming that endogenous hydrogen sulfide signaling is the active ingredient in the response. Mechanistically, exogenous NaHS significantly boosted the activities of L-cysteine desulfhydrase and D-cysteine desulfhydrase, the two key enzymes that produce hydrogen sulfide inside plant cells, thereby amplifying the plant’s own supply of the gas. That internal surge then enhanced the activity of 9-cis-epoxycarotenoid dioxygenase, the rate-limiting enzyme in abscisic acid biosynthesis, raising endogenous abscisic acid levels and setting off the hormone’s well-known protective program.

With the hydrogen sulfide-abscisic acid module activated, okra seedlings mounted a coordinated defense on several fronts simultaneously. The treated plants accumulated higher levels of proline, soluble proteins and soluble sugars, a trio of osmoprotectants that helps cells retain water and maintain turgor under saline conditions. At the same time, NaHS treatment restrained the excessive accumulation of sodium ions while preserving potassium retention, restoring the favorable potassium-to-sodium ratio that is a hallmark of salt-tolerant plants. Because potassium is essential for enzyme function and photosynthesis, keeping sodium out and potassium in is arguably the single most important determinant of whether a seedling survives a salty growing season.

The photosynthetic machinery benefited as well. Salt-stressed okra that received NaHS preserved its contents of chlorophyll a, chlorophyll b and carotenoid pigments, the molecular antennas that capture light energy. Pigment degradation is a classic symptom of salt injury, and its prevention translated directly into maintained growth. Membrane damage, measured by malondialdehyde accumulation and electrolyte leakage, was markedly reduced, indicating that cellular barriers stayed intact rather than falling victim to salt-induced lipid peroxidation.

Perhaps the most detailed part of the study concerned redox homeostasis, the delicate balance between the production and destruction of reactive oxygen species. Salt stress floods plant cells with hydrogen peroxide and superoxide radicals, which damage proteins, membranes and DNA if left unchecked. The researchers found that hydrogen sulfide-dependent signaling strengthened the activities of antioxidant enzymes and remodeled the ascorbate-glutathione cycle, a central metabolic loop in which ascorbate and glutathione shuttle electrons to neutralize peroxides. With this cycle running at full capacity, the excess hydrogen peroxide and superoxide generated by salt stress were effectively scavenged before they could inflict lasting harm.

To make sense of the many measured variables, the team applied hierarchical cluster analysis and Pearson correlation analysis across the physiological indicators. The statistical picture that emerged suggested that endogenous hydrogen sulfide acts as an upstream core signal, sitting near the top of the regulatory hierarchy and coordinating seedling growth, photosynthetic pigment stability, ion balance and redox homeostasis under salt stress. In other words, rather than merely patching one symptom, the gas appears to orchestrate a whole-plant adaptation program, with abscisic acid acting as a key downstream executor that mobilizes osmotic adjustment, ion control and antioxidant defenses in concert.

The broader significance of the work lies in positioning hydrogen sulfide as an upstream gaseous regulator of plant salt adaptation, a role that complements recent discoveries about protein persulfidation, the chemical modification through which hydrogen sulfide alters the behavior of signaling proteins in crops ranging from rice to Arabidopsis. By demonstrating that a cheap, water-soluble donor like NaHS can activate the endogenous hydrogen sulfide-abscisic acid cascade in an economically important vegetable, the study provides a preliminary scientific rationale for foliar-application trials of okra on salinized agricultural land. The authors are careful to note that their results come from controlled germination and pot experiments, and that field-scale validation, including optimal dosing, application timing and safety assessment, remains the necessary next step. Still, the prospect of a single foliar spray that simultaneously protects membranes, preserves photosynthesis, balances ions and quenches reactive oxygen is an attractive one for growers confronting degrading soils. As salinity continues to encroach on arable land across the globe, the humble molecule that smells of rotten eggs may prove to be an unexpected ally in keeping crops alive and productive.

Subject of Research: Hydrogen sulfide and abscisic acid signaling in salt-stress tolerance of okra seedlings

Article Title: Exogenous NaHS-derived H2S alleviates salt stress in okra via H2S-ABA signaling and redox homeostasis

Article References: Wang, F., Chen, X., Li, N., Pei, B., Chen, X., & Ye, Y. (2026). Exogenous NaHS-derived H2S alleviates salt stress in okra via H2S-ABA signaling and redox homeostasis. Plant and Soil. https://doi.org/10.1007/s11104-026-09123-0

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09123-0

Keywords: okra, salt stress, hydrogen sulfide, sodium hydrosulfide, abscisic acid, redox homeostasis, AsA-GSH cycle, ion homeostasis, osmotic adjustment, reactive oxygen species, plant signaling, soil salinity