Overview
Chen and colleagues tested how cadmium stress and abscisic acid (ABA) treatment affect cadmium (Cd) uptake and tissue distribution in ramie, a non-food fiber crop proposed for phytoremediation of Cd-contaminated soil. This is remediation and plant-uptake mechanism evidence, not occurrence evidence for edible rice, salt, textiles, or consumer products.
Key numbers
The paper frames ramie as a high-biomass remediation crop and cites annual dry matter production up to 42 t per hectare per year. The authors state that heavy metals absorbed by ramie are mainly distributed in the root, with little in the fiber, and that absorbed metals are removed during fiber degumming rather than entering the food chain.
The Cd-stress experiment used hydroponic ramie cuttings of Zhongzhu No. 2 treated with 0, 5, 10, 15, and 30 mg/L CdCl2. New leaves, old leaves, and roots were sampled for ABA at 0, 3, 10, 20, and 32 days. The fourth fully expanded leaf was used for chlorophyll measurement after 25 days of treatment. Three independent biological replicates were established for each control and Cd treatment, each replicate consisting of ten ramie plants; Figure 1 states that chlorophyll and shoot-Cd endpoints used material from five plants per replicate.
Figure 1 reports that shoot Cd content increased with increasing CdCl2 dose, while chlorophyll b and total chlorophyll decreased significantly under Cd treatment. Chlorophyll a was significantly reduced only at the high 30 mg/L CdCl2 treatment. Plant-height and root-length growth rates were higher than control below 10 mg/L CdCl2 and significantly lower above 15 mg/L CdCl2.
The ABA-treatment experiment exposed ramie to 15 mg/L CdCl2 for 4 days, then applied ABA by two routes: spraying ABA on ramie plants (SORP) or adding ABA directly to the culture solution (ADCS). ABA concentrations were 0, 0.01, 0.05, 1, 2.5, 5, 20, and 40 uM. Plant height and root length were measured after 10 days of ABA treatment; leaves, stems, and roots were harvested for Cd content after 20 days.
Figure 2 reports that, under SORP, root Cd content was highest, stem Cd content intermediate, and leaf Cd content lowest. Total Cd content at 0.01, 1, 2.5, 5, and 40 uM ABA was significantly higher than the control, indicating that foliar ABA promoted Cd absorption. Under ADCS, total Cd absorption was higher than control at all ABA treatments except 0.01 uM. High ADCS concentrations above 20 uM caused root decay and negative root-growth rates.
The authors identify different practical optima for growth and Cd enrichment. Spraying ABA below 2.5 uM was described as most suitable for promoting ramie growth under Cd stress, while Figure 2B shows the highest Cd content when spraying 5 uM ABA.
Methods (brief)
Ramie variety Zhongzhu No. 2 was grown hydroponically in 1/4 Hoagland nutrient solution at 26 C, 70% relative humidity, 300 umol/m2/s light, and a 12-hour light/dark cycle. Cd stress was applied as CdCl2. ABA was applied either by foliar spraying or direct addition to the culture solution. Cd content was measured on dried plant tissue using a SOLAAR M6 atomic absorption spectrometer. ABA was measured with a plant ABA ELISA kit. Chlorophyll was measured from fresh leaves soaked in 95% ethanol. Gene expression was measured by q-PCR using 18S rRNA as the internal control, and statistics used one-way ANOVA with LSD comparisons at P = 0.05.
Related evidence
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