article · Frontiers in Plant Science
High levels of sodium disrupt metabolic processes and reduce plant growth. This research clarifies the physiological and genetic mechanisms driving salt tolerance in alfalfa by comparing a tolerant genotype, Zhongmu, with a sensitive genotype, Xingjiang Daye. Under severe salt stress, the sensitive plants experienced notable growth reductions and oxidative stress, alongside increased sodium uptake and reduced potassium levels. In contrast, the tolerant Zhongmu plants maintained favourable ion balances by extruding excess sodium, driven by the elevated expression of transporter genes including SOS1, NHX1, and HKT1. Zhongmu also exhibited higher lignin accumulation, supported by the upregulation of key lignin biosynthesis genes such as 4CL2, CCoAOMT, and PAL1. Additionally, enhanced activities of antioxidant enzymes, including catalase and superoxide dismutase, shielded the tolerant variety from oxidative damage. These combined responses explain the functional basis of salinity resilience in alfalfa.
Soil salinity is a major threat to agricultural productivity, restricting crop growth and reducing usable farmland. By explaining how tolerant alfalfa plants regulate sodium transport, strengthen cell walls through lignin production, and deploy antioxidant defences, this work pinpoints key biological pathways that govern stress adaptation. Understanding these mechanisms helps researchers identify functional targets for developing hardier forage crops suitable for marginal, salt-affected land.
This work represents early-stage discovery research that identifies genetic targets and physiological markers governing salinity tolerance in alfalfa. Plant breeding organisations, seed companies, and agricultural biotechnology researchers could utilise these specific transporter and lignin genes to develop molecular markers for selective breeding or gene-editing programmes. Because the study focuses on comparative laboratory profiling rather than field-tested commercial cultivars, translation into marketable, salt-resilient seed products remains at a pre-commercial stage of development.
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Accumulation of high sodium (Na<sup>+</sup>) leads to disruption of metabolic processes and decline in plant growth and productivity. Therefore, this study was undertaken to clarify how Na<sup>+</sup>/H<sup>+</sup> exchangers and Na<sup>+</sup>/K<sup>+</sup> transporter genes contribute to Na<sup>+</sup> homeostasis and the substantial involvement of lignin biosynthesis genes in salt tolerance in alfalfa (<i>Medicago sativa</i> L.), which is poorly understood. In this study, high Na<sup>+</sup> exhibited a substantial reduction of morphophysiological indices and induced oxidative stress indicators in Xingjiang Daye (XJD; sensitive genotype), while Zhongmu (ZM; tolerant genotype) remained unaffected. The higher accumulation of Na<sup>+</sup> and the lower accumulation of K<sup>+</sup> and K<sup>+</sup>/(Na<sup>+</sup> + K<sup>+</sup>) ratio were found in roots and shoots of XJD compared with ZM under salt stress. The ZM genotype showed a high expression of <i>SOS1</i> (<i>salt overly sensitive 1</i>), <i>NHX1</i> (<i>sodium/hydrogen exchanger 1</i>), and <i>HKT1</i> (<i>high-affinity potassium transporter 1</i>), which were involved in K<sup>+</sup> accumulation and excess Na<sup>+</sup> extrusion from the cells compared with XJD. The lignin accumulation was higher in the salt-adapted ZM genotype than the sensitive XJD genotype. Consequently, several lignin biosynthesis-related genes including <i>4CL2, CCoAOMT, COMT, CCR, C4H</i>, <i>PAL1</i>, and <i>PRX1</i> exhibited higher mRNA expression in salt-tolerant ZM compared with XJD. Moreover, antioxidant enzyme (catalase, superoxide dismutase, ascorbate peroxidase, and glutathione reductase) activity was higher in ZM relative to XJD. This result suggests that high antioxidant provided the defense against oxidative damages in ZM, whereas low enzyme activity with high Na<sup>+</sup> triggered the oxidative damage in XJD. These findings together illustrate the ion exchanger, antiporter, and lignin biosysthetic genes involving mechanistic insights into differential salt tolerance in alfalfa.
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DOI: 10.3389/fpls.2022.1041764
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