Urban ornamental shrubs have significant potential for restoring cadmium (Cd)-contaminated soil. The Cd enrichment characteristics and tolerance mechanisms of Buxus sinica and Ligustrum x vicaryi were investigated through a simulated pot pollution experiment. Specifically, the Cd content and accumulation in different plant tissues, the subcellular distribution and chemical forms of Cd in the roots, and the effects of Cd on the ultrastructure of root cells under various Cd concentrations (0, 25, 50, 100, and 200 mg kg-1) were analyzed. The results showed that: (1) As the Cd treatment levels increased, the total biomass of B. sinica gradually decreased, while L. x vicaryi exhibited a stimulation effect at low Cd concentrations but inhibition at high Cd concentrations. (2) The Cd content in different tissues of both shrubs increased with rising Cd levels. The bioconcentration factor (BCF) and translocation factor (TF) indicated that L. x vicaryi has the potential for Cd phytostabilization. (3) Cd in the roots of both shrubs was primarily present in NaCl-extractable form, and was mostly bound to the cell wall. (4) Excessive Cd caused damage to the cellular structure of B. sinica, while the cells of L. x vicaryi maintained normal morphology. (5) In both shrubs, Cd primarily bound to the cell wall through hydroxyl and amino functional groups, as well as soluble sugars. In summary, converting Cd to less active forms, immobilizing Cd in the cell wall, and providing binding sites through functional groups may be crucial resistance mechanisms for both shrubs in response to Cd stress.

The gap between serious soil heavy metals pollution and inefficient soil remediation threatens human health. This study proposed a method to improve the phytoremediation efficiency using bamboo vinegar (BV) solution and the potential mechanism was discussed. The results demonstrated that the application of BV increases the content of cadmium (Cd) in vacuole and cell wall hemicellulose 2 in leaves of Perilla frutescens. Simultaneously, it enhanced enzyme activities of superoxide dismutase and catalase in leaves. Therefore, this process alleviated the damage of Cd to functional tissues of Perilla frutescens, thus improving the tolerance of plants to Cd. Moreover, the BV application reduced the Cd content bound by root cell wall pectin fractions and insoluble phosphate, subsequently improving the ability of oxalic acids to carry Cd to the aerial parts. Consequently, the aerial parts obtained a larger amount of Cd enrichment. Overall, the Transfer Factor of Cd from roots to stems and enrichment of Cd in Perilla frutescens were maximally increased by 57.70 % and 54.03 % with the application of 50-fold and 300-fold diluted BV under 2 mg & sdot;L- 1 Cd stress, respectively. The results can provide a theoretical basis for the promotion of phytoremediation of Cd-contaminated soil treatment technology.

Background and aimsCadmium (Cd) contamination poses a potential threat to plant growth and human health. In this study, we aimed to determine the effect of selenium nanoparticles (SeNPs) on Cd and selenium (Se) uptake and accumulation in bok choy, and investigate the detoxification mechanism of SeNPs on bok choy under Cd stress.MethodsA pot culture was performed in Cd-contaminated soil with soil applied and foliar-sprayed SeNPs, including SLow, SHigh, FLow, FHigh, and corresponding control treatment. The soil available Cd content, Cd and Se fractions in soil, elements accumulation, subcellular Cd/Se distribution, MDA content, SOD activity, and Fourier transformed infrared spectroscopy (FTIR) were evaluated.ResultsSoil applied SeNPs significantly reduced Cd concentration by 25.9-42.4%, and Cd uptake rate by 33.4-37.8%. Further, soil applied SeNPs had no significant effect on available Cd but did affect Se fractions in soil. Additionally, soil applied SeNPs increased Se concentration by 3.1 - 6.3 times in bok choy and caused a higher Se concentration in root than in shoot, with the residual and organic matter-bound Se mainly affecting Se accumulation in shoot. However, foliar-sprayed SeNPs had no significant effect on Cd uptake but increased Se accumulation by 2.4 - 33.0 times in bok choy. Soil applied and foliar-sprayed SeNPs prompted the distribution of Cd in cell wall and in soluble component in shoot, respectively, which reduced the damage of Cd on organelle.ConclusionSoil applied SeNPs was an effective method for reducing Cd accumulation and improving Se biofortification and mineral elements accumulation in bok choy.