Competitive ion uptake and transcriptional regulation as a coordinated dual mechanism of NaCl-mediated cadmium detoxification in Suaeda salsa

Abstract

Cadmium (Cd), a highly toxic heavy metal, severely inhibits plant growth. Salt alleviates Cd stress in halophytes, however, the molecular mechanisms governing salt-mediated regulation of Cd toxicity remain poorly understood. This study elucidates the protective mechanism of NaCl in Cd-stressed Suaeda salsa seedlings. Cd exposure suppressed seedling growth and induced membrane lipid peroxidation. Conversely, NaCl application not only maintained normal growth but also effectively ameliorated Cd-induced phytotoxicity, potentially through osmotic adjustment mechanisms. Notably, using ion flux analysis, we found that NaCl attenuated Cd²⁺ influx into root epidermal cells, thereby enhancing Cd resistance. Pharmacological inhibition studies confirmed that Na ⁺ competitively inhibits Cd²⁺ uptake through shared channels/transporters. Furthermore, RT-qPCR gene expression profiling revealed that NaCl coordinately activated both ionic compartmentalization and efflux systems through upregulating plasma membrane-localized SsSOS1 and tonoplast-associated SsNHX1 for Na ⁺ extrusion and vacuolar sequestration, enhancing Cd²⁺ compartmentalization via SsCAX and SsVHA-B mediated transport and maintaining cellular homeostasis through SsHKT1 and SsPIP-mediated regulation of water and K⁺ balance, or indirectly inhibit Cd²⁺ influx. It reveals that salt weakens Cd²⁺ influx and enhances Cd tolerance by activating a coordinated gene regulatory network in Suaeda salsa. This finding offers valuable insights into phytoremediation strategies for enhancing crop resilience in Cd-contaminated saline soils.