Main Content of the Evaluation of Cadmium Accumulation, Transport Characteristics, and Cadmium Tolerance in Various New Ramie Lines

I. Research Background and Objectives

• Cadmium (Cd) is highly toxic to living organisms and can easily harm human health through the food chain. Among heavy metals, soil contamination with Cd is the most severe in China. Remediation of heavy metal pollution is a critical issue for agricultural safety and sustainable development.
• Phytoremediation technology stands out for its low cost and environmental friendliness, but existing hyperaccumulator plants have limitations such as slow growth, low biomass, and low economic value.
• Ramie (Boehmeria nivea L.) has well-developed roots, high biomass, strong stress resistance, high economic value, and significant tolerance and adsorption capacity for heavy metals, demonstrating great potential for application in phytoremediation.
• This study aims to evaluate the Cd accumulation, transport characteristics, and Cd tolerance of five new ramie lines (H1–H5), using Zhongzhu No. 1 (Z1) as the control, thereby providing a scientific basis for breeding new ramie varieties specialized in heavy metal remediation.

II. Research Materials and Methods

(I) Experimental Materials

• Test materials: Zhongzhu No. 1 (Z1, a major cultivar in Hunan with high Cd tolerance and accumulation capacity) and five new ramie lines (H1–H5, with stable agronomic traits and good stress resistance).
• Cd stress reagent: CdCl₂•2.5H₂O, with a fixed Cd²⁺ concentration of 40 mg/L.

(II) Experimental Methods

1. Hydroponic experiment: Lateral branches of ramie were cut and rooted hydroponically prior to Cd stress treatment. The control group received no Cd supplementation. The culture conditions were set at 24–26°C, with a light intensity of 300 µmol/m²/s and a light cycle of 14 hours of light followed by 10 hours of darkness.
2. Measured indicators: Plant height, root length, and leaf SPAD value (relative chlorophyll content) were measured regularly after treatment. After 15 days of treatment, biomass (above-ground and below-ground dry weight), physiological and biochemical indicators (proline (Pro), malondialdehyde (MDA), etc.), and Cd accumulation and transport-related indicators (transport factor (TF), bioconcentration factor (BCF)) were determined.
3. Data processing: Membership function analysis and principal component analysis were used to comprehensively evaluate the Cd tolerance and Cd accumulation capacity of each material.

III. Key Research Findings

(I) Effects of Cd Stress on Ramie Growth

• Cd stress significantly inhibited the growth of the aboveground and underground parts of all test materials, reduced biomass accumulation, and caused wilting and even death in some plants.
• After 15 days of Cd stress, the root length growth of the five new lines was greater than that of Z1 (H1 showed the highest growth, 203.43% greater than Z1), and the biomass ranking was H1 > H4 > H5 > Z1 > H3 > H2.

(II) Changes in Physiological and Biochemical Indicators

• Leaf SPAD value: All materials showed a decrease under Cd stress, with Z1 exhibiting the largest decrease (29.47%), and the new lines showing smaller decreases. The ranking was H1 > H5 > H4 > H2 > H3 > Z1.
• Antioxidant system: Z1 showed the most significant increase in Pro content (647.54%); H1 showed the most significant increase in CAT activity (248.86%); SOD and POD activities increased to varying degrees under Cd stress.

(III) Cd Accumulation and Transport Characteristics

• The Cd concentration in the underground and aboveground parts, as well as the total Cd accumulation per plant, were highest in Z1, and all new lines had lower values than Z1.
• Transport factor (TF): H1 was the highest, 132.86% higher than Z1; Bioconcentration factor (BCF): Z1 was the highest, and all new lines were lower than Z1.

(IV) Comprehensive Evaluation Results

• Cd tolerance ranking: H4 > H5 > H1 > H3 > H2 > Z1 (H4 had the highest Cd tolerance).
• Ranking of Cd accumulation capacity: Z1 > H3 > H2 > H1 > H4 > H5 (Z1 had the highest accumulation capacity).

IV. Research Conclusions

This study clarified the differences in Cd tolerance and Cd accumulation capacity among six ramie varieties. H4 exhibited the highest Cd tolerance, while Z1 still demonstrated the highest Cd accumulation capacity. The research results expanded the resources available to heavy metal remediation facilities and provided a scientific basis for the targeted breeding of new ramie varieties specialized in heavy metal remediation. Further verification of the field heavy metal remediation capacity of these new lines is needed in the future.