Influencing Factors of Bidens pilosa L. Hyperaccumulating Cadmium Explored by the Real-Time Uptake of Cd2+ Influx around Root Apexes under Different Exogenous Nutrient Ion Levels

Abstract

Though Bidens pilosa L. has been confirmed to be a potential Cd hyperaccumulator, the accumulation mechanism is not yet clear. The dynamic and real-time uptake of Cd2+ influx by B. pilosa root apexes was determined using non-invasive micro-test technology (NMT), which partly explored the influencing factors of the Cd hyperaccumulation mechanism under the conditions of different exogenous nutrient ions. The results indicated that Cd2+ influxes at 300 μm around the root tips decreased under Cd treatments with 16 mM Ca2+, 8 mM Mg2+, 0.5 mM Fe2+, 8 mM SO42− or 18 mM K+ compared to single Cd treatments. The Cd treatments with a high concentration of nutrient ions showed an antagonistic effect on Cd2+ uptake. However, Cd treatments with 1 mM Ca2+, 0.5 mM Mg2+, 0.5 mM SO42− or 2 mM K+ had no effect on the Cd2+ influxes as compared with single Cd treatments. It is worth noting that the Cd treatment with 0.05 mM Fe2+ markedly increased Cd2+ influxes. The addition of 0.05 mM Fe2+ exhibited a synergistic effect on Cd uptake, which could be low concentration Fe2+ rarely involved in blocking Cd2+ influx and often forming an oxide membrane on the root surface to help the Cd uptake by B. pilosa. The results also showed that Cd treatments with high concentration of nutrient ions significantly increased the concentrations of chlorophyll and carotenoid in leaves and the root vigor of B. pilosa relative to single Cd treatments. Our research provides novel perspectives with respect to Cd uptake dynamic characteristics by B. pilosa roots under different exogenous nutrient ion levels, and shows that the addition of 0.05 mM Fe2+ could promote the phytoremediation efficiency for B. pilosa.

Research progress of the detection and analysis methods of heavy metals in plants

“…NMT can perform 3D measurements of the samples in situ with high sensitivity and spatial resolution without causing damage or requiring marker sampling. It is simple to operate and can detect the dynamic indicators of bioactivities of plants ( Yuan et al., 2021 ; Wang et al., 2023 ). It can detect 50 types of metallic molecules and ions, including H + , Ca 2+ , Na + , K + , Cl - , Cd 2+ , Cu 2+ , and NH 4 + ( Mugnai et al., 2012 ; Mardones et al., 2018 ; Wu et al., 2019 ; Lan et al., 2020 ; Zhang et al., 2020 ; Di et al., 2021 ; Hou et al., 2021 ).…”

“…The scanning ion selective electrode technology (SIET) and microelectrode ion flux estimation technology (MIFE) are commonly used for measuring ion currents in plants ( Mardones et al., 2018 ; Hou et al., 2021 ; Sun et al., 2021 ; Sun et al., 2021 ; Deng et al., 2022 ). The inflow of Cd 2+ at 300 µm around the root tips of Bidens pilosa L. plants was reduced when treated with 16 mM Ca 2+ , 8 mM Mg 2+ , 8 mM SO 4 2- , or 18 mM K + as detected by NMT, indicating that treatment at a large concentration of nutrient ions inhibited the absorption of Cd 2+ ( Wang et al., 2023 ). Using the NMT method, a peak in the net Cd 2+ flux was observed at a distance of 100 µm from the surface of the root tips of Amaranthus hypochondriacus L., a plant famous for its ability to accumulate large quantities of this metal ion ( Han et al., 2023 ).…”

Synergistic Effects of Exogenous Nutrient Ions on the Real-Time Cadmium Extraction by an Accumulator

“…The 10 µM Cd treatments combined with two concentration gradients were selected for each nutrient ion (e.g., Ca 2+ was supplied as Ca (NO 3 ) 2 , Mg 2+ as MgSO 4 , Fe 3+ as Fe-EDDHA, S as MgSO 4 , and K + as KNO 3 ) by adjusting the corresponding ionic concentrations in 1/5 strength solutions. The 12 treatments with a 1/5 strength Hoagland solution were listed as follows: (1) [15][16][17][18]. But the designs of the Cd treatment group with high concentrations of ions were according to the results of the pre-experiments.…”

Editorial for the Special Issue “Phytotoxicity of Heavy Metals in Contaminated Soils”

“…The bioavailability and plant uptake capacity of heavy metals also depends on the concentration of nutrients in the soil solution. Wang and co-authors [ 5 ] observed how Cd uptake by Bidens pilosa L. changes in a 10 μM Cd 2+ solution by varying the concentration of nutrients (Ca 2+ , Mg 2+ , Fe 2+ , SO 4 2− , Na + and K + ). High nutrient concentrations showed an antagonistic effect on root uptake of Cd 2+ , while Fe 2+ , at low concentrations, showed a synergistic effect on Cd 2+ uptake, forming an oxide membrane on the root surface to promote Cd uptake by B. pilosa .…”