Exploring the mechanisms by which sodium promotes growth of euhalophytes under potassium deficiency: A case study of Suaeda salsa

Abstract

Suaeda salsa L. is a leaf succulent euhalophyte. Its leaves are rich in secondary metabolites, such as polyphenols and flavonoids, which enhance its salt tolerance and have industrial value in pharmaceuticals, antioxidants, and food additives. Its growth is promoted under moderate salinity conditions. However, the mechanisms by which euhalophytes maintain a balance between growth and salt stress tolerance have not been elucidated, especially under K⁺ deficiency. Here, we used multi-omics and physiology analyses to investigate the role of Na⁺ in the growth and metabolic processes of S. salsa. Exogenous NaCl application significantly enhanced the photosynthetic efficiency of S. salsa under K⁺ deficiency, including the net photosynthetic rate, PSII photochemistry (Fv/Fm), photochemical quenching (qP), non-photochemical quenching (NPQ), and the activities of enzymes such as ferredoxin-NADP⁺ reductase (FNR) and Rubisco. Meanwhile, transcriptomic analysis revealed that NaCl treatment upregulated genes related to photosynthetic subunits, light-harvesting complexes (LHCs), and key Calvin cycle enzymes, including phosphoglycerate kinase (PGK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and Rubisco. These findings provide strong molecular evidence for the observed recovery of photosynthetic efficiency in NaCl-treated S. salsa under K⁺ deficiency. Furthermore, the relative contents of flavonoids and isoflavonoids, including isorhamnetin, isolupalbigenin, osajin, corylin, and wedelolactone, as well as unsaturated fatty acids (9-Hexadecenoic acid), were significantly upregulated treating with NaCl and KCl. These results suggest that S. salsa can utilize Na⁺ to enhance photosynthesis under high salinity and low K⁺ conditions, thereby enabling it to balance salt tolerance and growth. Our findings elucidate the key mechanisms underlying the critical role of Na⁺ in the physiological and metabolic processes of halophytes, providing a theoretical basis for the development of saline agriculture.