Temperature Dependence of Metals Accumulation and Removal Kinetics by Arabidopsis halleri ssp. gemmifera.

Cadmium (Cd), which is present in zinc (Zn) ore, is a toxic metal and causes contamination globally. Phytoremediation is a promising technology for the remediation of sites with low and moderate contamination. Temperature is an important factor in phytoremediation because it has an impact on both plant biomass and the accumulation of heavy metals. However, little is known about the influence of temperature on heavy metal accumulation by the Cd and Zn hyperaccumulator Arabidopsis halleri ssp. gemmifera. The effect of temperature on the distribution of Cd and Zn in A. halleri ssp. gemmifera and the mechanism of metal removal from solution were investigated in this study. Our results showed that the temperature dependence of the distribution of Cd and Zn in the plant was different, which may suggest that the mechanisms of xylem loading were different between Cd and Zn. Although Cd and Zn have partially similar transport pathways, the removal kinetics based on the first-order reaction rate constant revealed that the temperature which maximized rate of absorption was different between Cd and Zn. This study suggests a potential for efficient Cd phytoextraction using A. halleri ssp gemmifera in Cd and Zn co-existing environments.

New evidence of arsenic translocation and accumulation in Pteris vittata from real-time imaging using positron-emitting 74As tracer.

Pteris vittata is an arsenic (As) hyperaccumulator plant that accumulates a large amount of As into fronds and rhizomes (around 16,000 mg/kg in both after 16 weeks hydroponic cultivation with 30 mg/L arsenate). However, the sequence of long-distance transport of As in this hyperaccumulator plant is unclear. In this study, we used a positron-emitting tracer imaging system (PETIS) for the first time to obtain noninvasive serial images of As behavior in living plants with positron-emitting 74As-labeled tracer. We found that As kept accumulating in rhizomes as in fronds of P. vittata, whereas As was retained in roots of a non-accumulator plant Arabidopsis thaliana. Autoradiograph results of As distribution in P. vittata showed that with low As exposure, As was predominantly accumulated in young fronds and the midrib and rachis of mature fronds. Under high As exposure, As accumulation shifted from young fronds to mature fronds, especially in the margin of pinna, which resulted in necrotic symptoms, turning the marginal color to gray and then brown. Our results indicated that the function of rhizomes in P. vittata was As accumulation and the regulation of As translocation to the mature fronds to protect the young fronds under high As exposure.