# Physiological and Transcriptional Characterization the Differential Responses of Two Sorghum bicolor × Sorghum sudanense Cultivars to Cadmium Stress

## TL;DR

This study explores how two types of Sorghum plants respond differently to cadmium stress, revealing mechanisms that could help in cleaning up contaminated soils.

## Contribution

The study identifies physiological and molecular mechanisms underlying cadmium tolerance in Sorghum bicolor × Sorghum sudanense cultivars.

## Key findings

- Cd-tolerant cultivar S6 showed milder growth inhibition and lower Cd translocation to shoots compared to the sensitive cultivar.
- S6 maintained higher chlorophyll and photosynthetic efficiency, with upregulated antioxidant enzyme genes under Cd stress.
- Transcriptomic analysis revealed key genes and pathways in S6 related to Cd sequestration, detoxification, and stress response.

## Abstract

It is estimated that at least 16.1% of croplands in China are polluted with heavy metals, and cadmium (Cd) is a typical toxic element inhibiting plant growth. Sorghum bicolor × S. sudanense, a C4 plant with high biomass and stress tolerance, has potential for phytoremediation, but its Cd tolerance mechanism remains unclear. In this study, physiological and transcriptomic responses of Cd-tolerant (S6) and sensitive (2190A/201900131) cultivars were analyzed under 25 mg/L Cd stress. The results showed that S6 exhibited milder phenotypic inhibition (leaf yellowing, growth retardation) than the sensitive cultivar. Cd was mainly accumulated in roots (S6: 4988.37 mg/kg; sensitive: 7030.06 mg/kg at 7 d), with S6 having a lower translocation factor. Physiologically, S6 maintained higher chlorophyll content, stable photosynthetic efficiency (Fv/Fm, PI), and lower malondialdehyde (MDA) accumulation, while antioxidant enzyme (SOD, CAT, APX) genes were significantly upregulated. Transcriptomic analysis identified 47,797 differentially expressed genes (DEGs), enriched in glutathione metabolism, ABC transporter-mediated transport, metal chelation, and antioxidant defense pathways. Genes related to cell wall biosynthesis, metal transporters (ZIP, HMA), and transcription factors (MYB, WRKY) were synergistically upregulated in S6, enhancing Cd sequestration and detoxification. These findings clarify the physiological and molecular mechanisms of Cd tolerance in Sorghum bicolor × S. sudanense, providing a basis for its application in Cd-contaminated soil phytoremediation.