Wheat Seeds Show a Hormone Tipping Point Between Growth and Stress

Wheat feeds more than 40 percent of the world’s population, and every harvest begins with a seed germinating in the dark, moist soil. Now a research team at Suzhou University in China has mapped, in unprecedented molecular detail, how germinating wheat seeds respond to abscisic acid, the plant stress hormone that governs the delicate balance between growth and survival. The study, published in Frontiers in Plant Physiology, combined physiological measurements, transcriptome sequencing, and metabolomic profiling to reveal how a single hormone can rewire the entire gene expression and metabolic landscape of a germinating seed.

The researchers applied exogenous abscisic acid, commonly abbreviated ABA, to germinating wheat seeds at four concentrations: zero as a control, 2, 4, and 6 milligrams per liter. Their physiological measurements revealed a striking biphasic response. At the lowest dose, 2 milligrams per liter, primary root length actually increased by about 12 percent compared with untreated seeds. But at 4 milligrams per liter and above, growth was significantly inhibited, and at 6 milligrams per liter root length dropped by a dramatic 40 percent. This concentration-dependent switch between promotion and inhibition mirrors the classic biphasic behavior of ABA documented in other plant species, but the team wanted to understand what was happening inside the seed at the molecular level.

Physiological markers told a story of progressive oxidative stress. As ABA concentrations rose, the researchers measured increasing levels of electrolyte leakage, malondialdehyde, and catalase activity, all statistically significant at the higher doses. Electrolyte leakage signals damage to cell membranes, malondialdehyde is a well-established byproduct of membrane lipid peroxidation, and catalase is a key antioxidant enzyme that breaks down hydrogen peroxide. Together, these markers indicate that high ABA concentrations trigger a burst of reactive oxygen species that overwhelms the seed’s antioxidant defenses, leading to membrane damage and metabolic dysfunction. The team identified roughly 4 milligrams per liter as the threshold beyond which oxidative damage becomes pronounced.

To peer inside the molecular machinery, the researchers sequenced the transcriptomes of seeds treated with 6 milligrams per liter ABA and compared them with untreated controls. They identified 854 differentially expressed genes, with 470 up-regulated and 384 down-regulated. Gene Ontology enrichment showed that these genes were predominantly involved in cellular processes, metabolic processes, catalytic activity, and transporter activity, suggesting a broad remodeling of the seed’s biochemical and transport networks. KEGG pathway analysis highlighted the activation of linoleic acid metabolism, alpha-linolenic acid metabolism, glycolysis and gluconeogenesis, and the biosynthesis of amino acids, pathways that collectively point to ROS scavenging, energy provision, and protein homeostasis as central themes of the ABA response.

The metabolomic analysis was equally revealing. Untargeted liquid chromatography mass spectrometry detected more than 21,000 metabolic features, annotated as over 6,000 compounds, and identified 665 differentially accumulated metabolites between the control and high-ABA treatments, with 345 up-regulated and 320 down-regulated. Lipids constituted the largest altered category at 15.5 percent of the differentially accumulated metabolites, followed by ketones, aldehydes, and esters at 15.6 percent, with organic acids, saccharides, terpenoids, and amino acids also showing significant changes. KEGG enrichment singled out benzoxazinoid biosynthesis and nicotinate and nicotinamide metabolism as the pathways with the largest shifts, suggesting that the seed mobilizes defensive secondary metabolites and NAD-related metabolism in response to the hormone stress.

The real power of the study came from integrating the two data streams. Co-expression network analysis revealed strong positive correlations between differentially expressed genes and differentially accumulated metabolites, and joint KEGG enrichment identified 10 core pathways that orchestrate the ABA response, including glycolysis and gluconeogenesis, amino acid biosynthesis, cysteine and methionine metabolism, starch and sucrose metabolism, and ABC transporters. Crucially, the analysis pinpointed two types of hub nodes that appear repeatedly across multiple pathways. The metabolite L-serine was enriched in five separate pathways, acting as a carbon-nitrogen flux node that balances resource allocation. On the gene side, TraesCS3A02G276100, a glycolytic enzyme gene, co-regulated starch and sucrose metabolism, fructose and mannose metabolism, and glycolysis, coordinating carbon partitioning for energy homeostasis. Another gene, TraesCS5A02G398300, modulated amino acid biosynthesis and cysteine and methionine metabolism, the latter supplying glutathione precursors for ROS scavenging.

Based on these findings, the researchers propose a working model in which energy supply through glycolysis, the ROS scavenging system, and nitrogen metabolism through amino acid balance form a functionally interconnected network that responds to high ABA stress. Under severe ABA treatment, the data suggest attenuated glycolysis, decreased ATP levels, altered amino acid profiles, and accumulated ROS, collectively pointing to a state of overall metabolic dysfunction. The team emphasizes that this model is built on correlative data and that future functional validation through gain-of-function and loss-of-function experiments, along with metabolic flux analysis, will be needed to establish causality.

The study also revealed an intriguing connection between ABA and linolenic acid metabolism. The recurrent enrichment of the gene TraesCS5B02G078300 suggests that ABA promotes the synthesis of jasmonate precursors, signaling molecules involved in plant defense. Meanwhile, the activation of benzoxazinoid biosynthesis points to the mobilization of secondary metabolites that mitigate oxidative damage. The researchers propose an ABA-induced adaptation axis in which the hormone triggers lipid oxidation for signaling while simultaneously mobilizing protective secondary metabolites to counter the oxidative stress it provokes.

The implications extend beyond basic plant biology. ABA is already known to enhance carbohydrate accumulation and remobilization to grains in wheat under water stress, and foliar ABA application has been shown to increase yield in field conditions. By identifying the molecular hubs and core pathways that respond to exogenous ABA, this study lays a theoretical foundation for developing ABA-based seed treatment technologies and stress-resistant breeding strategies. The researchers suggest that future studies could refine the dose-response relationship by incorporating wider concentration gradients and calculating the half-maximal inhibitory concentration, providing a more quantitative framework for agricultural applications.

What makes this study particularly compelling is the elegance of the biphasic response it documents. A single hormone, applied at different concentrations, can either gently nudge a germinating seed toward enhanced growth or push it into a full-blown stress response with membrane damage and metabolic collapse. The identification of L-serine and specific multi-pathway genes as critical network nodes offers concrete molecular targets for future crop improvement efforts. As climate change intensifies abiotic stresses on global agriculture, understanding how the world’s most important cereal crop fine-tunes its gene expression and metabolic networks in response to a key stress hormone could prove invaluable for breeding the resilient wheat varieties of tomorrow.

Subject of Research: Integrated transcriptomic and metabolomic analysis of wheat germinating seed response to exogenous abscisic acid stress

Article Title: Integrated transcriptomic and metabolomic analysis reveals the molecular mechanisms underlying wheat germinating seed response to exogenous abscisic acid stress

Article References: Wang, X., Chen, C., Sun, X., & Wang, C. (2025). Integrated transcriptomic and metabolomic analysis reveals the molecular mechanisms underlying wheat germinating seed response to exogenous abscisic acid stress. Frontiers in Plant Physiology, 3, Article 1684534. https://doi.org/10.3389/fphgy.2025.1684534

Image Credits: AI Generated

DOI: 10.3389/fphgy.2025.1684534

Keywords: wheat, abscisic acid, seed germination, transcriptomics, metabolomics, oxidative stress, multi-omics, metabolic reprogramming, plant physiology, stress response, L-serine, crop breeding