# Physiological and Molecular Mechanisms Underlying the Differential Responses of Wheat Seedlings to Different Types of Salt Stress

## TL;DR

This study explores how different types of salt stress affect wheat seedlings, revealing that alkaline salts cause more severe damage than neutral salts.

## Contribution

The study identifies distinct physiological and molecular mechanisms triggered by different salt types in wheat seedlings.

## Key findings

- Alkaline salts like Na2CO3 cause more severe growth inhibition and oxidative damage than neutral salts.
- Alkaline stress activates ascorbate defenses while neutral salts enhance catalase activity.
- Alkaline stress disrupts ion homeostasis with excessive Na+ uptake and K+ depletion.

## Abstract

Soil salinization, driven by rapid climate change, poses a serious threat to wheat (
Triticum aestivum
L.) production worldwide. The studies on the effect of sodium chloride stress on wheat have detailed reports, while the effects of Na2SO4, NaHCO3, and Na2CO3 stresses remain to be investigated. Here, we investigated the differential growth and physiological responses of wheat seedlings to equimolar concentrations of NaCl, Na2SO4, NaHCO3, and Na2CO3. Alkaline salts (NaHCO3 and Na2CO3) induced significantly more severe growth inhibition, chlorophyll degradation, and oxidative damage compared to neutral salts (NaCl and Na2SO4). This was evidenced by heightened lipid peroxidation, reactive oxygen species accumulation, and membrane injury, particularly under Na2CO3 stress. The antioxidant defenses were precisely tailored, which alkaline stress strongly activated ascorbate while neutral salts preferentially enhanced catalase activity. Osmotic adjustment was also stress‐specific, with alkaline conditions triggering extreme proline accumulation up to 7.5‐fold in roots. Ion homeostasis was profoundly disrupted under alkaline stress, marked by excessive Na+ uptake, severe K+ depletion, and significant reductions in nitrogen and phosphorus. Notably, gene expression analysis revealed stress‐specific regulation of key genes involved in ion transport (e.g., SOS1) and antioxidant defense. Our findings revealed distinct stress‐specific regulatory mechanisms in wheat, with alkaline causing more severe oxidative stress and membrane damage than salt. In addition, we examined the tissue expression and evolution of SOD genes, which showed the expansion and duplication of the SOD gene family in terrestrial plants. Our study unveils the divergent physiological pathways activated by different salts, providing novel insights into wheat stress adaptation and a theoretical basis for breeding salt‐tolerant cultivars.

Chinese Spring (CS), Qing Mai 6 (QM), ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), Peroxidase(POD), Malondialdehyde, (MDA).