Frontiers | The regulatory roles of flavonoids, melatonin, and glycine betaine in plant salt stress response

1 IntroductionAbiotic stresses pose significant threats to agricultural production worldwide, with salt stress being one of the most detrimental factors (Gong et al., 2020; Ma et al., 2025). High salinity restricts land usability and severely reduces crop yields by impairing plant growth and development (Su et al., 2020; Martínez Rivas et al., 2025). Salt stress induces a combination of primary and secondary stresses, including ion toxicity, osmotic stress, and oxidative damage (Yang and Guo, 2018a). These stresses collectively inhibit water uptake, disrupt cellular homeostasis, and impair photosynthesis (Yang and Guo, 2018b). In response, plants have evolved various adaptive mechanisms to maintain homeostasis and sustain growth under saline conditions. These strategies include osmotic adjustment, regulation of ion transport, and scavenging of reactive oxygen species (ROS) (Zelm et al., 2020; Zhao et al., 2021). Among these, metabolic regulation plays a particularly critical and dynamic role, enabling plants to undergo biochemical adjustments that support survival in harsh environments (Chapman and Muday, 2021).Plants biosynthesize a diverse array of low-molecular-weight metabolites that are essential for growth regulation, defense, and environmental adaptation (Zhao et al., 2019; Zhou et al., 2019; Maeda, 2019). These compounds are broadly categorized into primary metabolites, which sustain fundamental cellular processes; phytohormones, which coordinate development and stress signaling; and secondary metabolites, which primarily mediate plant-environment interactions (Erb and Kliebenstein, 2020). Importantly, the functional repertoire of key secondary metabolites extends beyond salt stress, serving as conserved mechanisms for abiotic stress tolerance more broadly. For instance, exogenous melatonin has been shown to enhance drought resilience by improving physiological traits and reprogramming stress-related metabolic pathways in species such as Taxus baccata and Prunus avium (Shahmohammadi et al., 2024; Hojjati et al., 2024). Similarly, glycine betaine application mitigates water deficit by supporting membrane integrity and biochemical functions (Annunziata et al., 2019). This findings underscore the fundamental role of these metabolites as broad-spectrum stress regulators, with this review focusing on their specific functions under saline conditions.Secondary metabolites comprising more than 200,000 structurally diverse compounds, are derived from primary metabolic pathways and include nitrogen-containing compounds, fatty acid derivatives, phenolics, alkaloids, terpenoids, benzenoids, indole and sulfur-containing indole compounds, and glucosinolates (Piasecka et al., 2015). These compounds are particularly significant in mediating plant responses to environmental cues, including salt stress (Yang et al., 2018). Their biosynthesis and accumulation are often triggered by specific stress conditions through changes in gene expression

Read More