Subcellular distribution and chemical forms of Cd in Bougainvillea spectabilis Willd. as an ornamental phytostabilizer: An integrated consideration

Response of Cd, Zn Translocation and Distribution to Organic Acids Heterogeneity in Brassica juncea L

In order to investigate the translocation, distribution, and organic acid heterogeneity characteristics in Brassica juncea L., a pot experiment with the exogenous application of Cd and Zn was conducted to analyze the effects of Cd, Zn, and organic acid contents and heterogeneity on the translocation and distribution of Cd and Zn. The results showed that the Cd and Zn contents of B. juncea were mainly accumulated in the roots. The Cd content in the symplast sap was 127.66-146.50% higher than that in the apoplast sap, while the opposite was true for Zn. The distribution of Cd in xylem sap occupied 64.60% under 20 mg kg^-1 Cd treatment, and Zn in xylem sap occupied 60.14% under 100 mg kg^-1 Zn treatment. The Cd was predominantly distributed in the vacuole, but the Zn was predominantly distributed in the cell walls. In addition, oxalic and malic acids were present in high concentrations in B. juncea. In the vacuole, correlation analysis showed that the contents of Cd were negatively correlated with the contents of oxalic acid and succinic acid, and the contents of Zn were positively correlated with the contents of malic acid and acetic acid. The contents of Cd and Zn were negatively related to the contents of oxalic acid and citric acid in xylem sap. Therefore, Cd in B. juncea was mainly absorbed through the symplast pathway, and Zn was mainly absorbed through the apoplast pathway, and then Cd and Zn were distributed in the vacuole and cell walls. The Cd and Zn in B. juncea are transferred upward through the xylem and promoted by oxalic acid, malic acid, and citric acid.

Chemical forms of cadmium in soil and its distribution in French marigold sub-cells in response to chelator GLDA

The use of degradable chelating agents to facilitate phytoextraction is a promising low-cost method for the remediation of heavy metal-contaminated soils. However, there are few studies on how plants and soils respond to the chelating agents. In this study, the responses of French marigold (Tagetes patula L.) and soil cadmium (Cd) to the chelator tetrasodium glutamate (GLDA) was investigated in a 180 d field trial. Five GLDA treatments (0, 292.5, 585, 1170, and 2340 kg hm-2) were carried out in a Cd-contaminated soil (0.47 mg kg-1) under French marigold plantation. The results showed that the application of GLDA promoted the transformation of other forms of Cd in soil to exchangeable state, and the exchangeable Cd and Fe-Mn oxide bound state increased by 42.13% and 32.97% (p < 0.05), respectively. The cell wall Cd accumulations significantly increased 9.39% (p < 0.05) and the percentages of soluble fractions increased by 460.33% (p < 0.05). Furthermore, increases occurred in soil pH, as well as DOC and DTPA-Cd contents with increasing the total amount of GLDA. The composite application of GLDA (2340 kg hm-2) with French marigold reduced the total soil Cd content by 7.59% compared with the soil background. Altogether, results of this study suggested that the application of GLDA can effectively activate soil Cd and enhance the capability of French marigold for the remediation of Cd-contaminated soils.

Cellular distribution of cadmium in two amaranth (Amaranthus mangostanus L.) cultivars differing in cadmium accumulation

Differences in cellular cadmium (Cd) distribution between Cd-tolerant and Cd-sensitive lines of amaranth (Amaranthus mangostanus L.) may reveal mechanisms involved in Cd tolerance and hyperaccumulation. We compared the cellular distribution and accumulation of Cd in roots, stems, and leaves between a low-Cd accumulating cultivar (Zibeixian, L-Cd) and a high-Cd accumulating cultivar (Tianxingmi, H-Cd) in a hydroponic experimental system. In all treatments, H-Cd grew better than L-Cd and accumulated more Cd. As the Cd concentration increased, the H-Cd plants grew normally and their biomass increased, except in the 60 μM Cd treatment. The biomass of L-Cd decreased with increasing Cd concentrations. The highest Cd concentration in the roots, stems, and leaves of H-Cd was 950 mg/kg, 305 mg/kg, and 205 mg/kg, respectively, compared with 269 mg/kg, 62.9 mg/kg, and 74.8 mg/kg, respectively, in L-Cd. The Cd distribution differed between the two cultivars. Scanning and transmission electron microscopy and energy-dispersive spectrometry analyses showed that Cd was distributed across the entire cross section of H-Cd roots but largely restricted to the epidermal cells and the exodermis of L-Cd roots. The main Cd storage sites were the root apoplast, cell walls, and intercellular spaces in H-Cd and the root epidermal cells and the exodermis in L-Cd. In H-Cd leaves, Cd accumulated mainly in vacuoles of epidermal cells and, at high external Cd concentrations, in the vacuoles of mesophyll cells.