# Physiological Differences and Transcriptional Regulatory Characteristics of Salt-Tolerant and Salt-Sensitive Grapevine Cultivars Under Salt Stress

## TL;DR

This study compares how two grapevine varieties respond to salt stress, finding that 'Carménère' is more salt-tolerant due to better physiological and molecular defenses.

## Contribution

The study identifies specific physiological and transcriptional mechanisms that enhance salt tolerance in 'Carménère' grapevines.

## Key findings

- Carménère showed less photosynthetic damage and better antioxidant activity under salt stress compared to Pinot Noir.
- Carménère accumulated more osmotic adjustment substances and maintained better ion balance under salt stress.
- Transcriptomic analysis revealed enriched pathways in hormone signaling and glutathione metabolism in Carménère under stress.

## Abstract

Salt stress is a major abiotic factor limiting grapevine growth and yield. To elucidate the physiological and molecular regulatory mechanisms underlying salt tolerance in grapevine, this study used ‘Carménère’ (Vitis vinifera) and ‘Pinot Noir’ (Vitis vinifera) as experimental materials. Under 200 mmol/L NaCl stress, the physiological response characteristics of the two cultivars were systematically compared, and transcriptome sequencing combined with qRT-PCR analysis was conducted to explore the molecular basis of their differences in salt tolerance. The results showed that salt stress significantly impaired photosynthetic performance and disrupted cellular homeostasis in grapevine; however, the reductions in relative chlorophyll content (SPAD value), maximum photochemical efficiency of photosystem II (Fv/Fm), and photosynthetic performance were significantly smaller in ‘Carménère’ than in ‘Pinot Noir’, indicating greater stability of the photosynthetic apparatus in ‘Carménère’. Meanwhile, ‘Carménère’ maintained higher activities of antioxidant enzymes and higher levels of non-enzymatic antioxidants, effectively reducing reactive oxygen species accumulation and membrane lipid peroxidation. In addition, under salt stress, ‘Carménère’ accumulated greater amounts of osmotic adjustment substances and maintained lower Na+ content and higher K+ content, demonstrating a more efficient capacity for osmotic regulation and ion homeostasis. Transcriptomic analysis revealed that the plant hormone signal transduction, MAPK signaling, and glutathione metabolism pathways were significantly enriched in ‘Carménère’, with multiple key genes being coordinately upregulated under salt stress. Taken together, these findings indicate that ‘Carménère’ achieves enhanced salt tolerance through a multilayered signaling regulatory network that coordinates physiological defense responses. This study provides a theoretical basis for elucidating the mechanisms of salt tolerance in grapevine and for the molecular breeding of salt-tolerant cultivars.