Roles of Chloride and Sulfate Ions in Controlling Cadmium Transport in a Soil-Rice System as Evidenced by the Cd Isotope Fingerprint.

Anions accompanying inorganic fertilizers, such as chloride and sulfate ions, potentially affect the solubility, uptake, and transport of Cd to rice grains. However, the role of anions in controlling Cd transport in the soil-soil solution-Fe plaque-rice plant continuum remains poorly understood. Cd isotope ratios were applied to Cd-contaminated soil pots, hydroponic rice, and adsorption experiments with or without KCl and K2SO4 treatments to decipher transport processes in the complex soil-rice system. The chloride and sulfate ions increased the Cd concentrations in the soil solution, Fe plaque, and rice plants. Accordingly, the magnitude of positive fractionation from soil to the soil solution was less pronounced, but that between soil and Fe plaque or rice plant is barely varied. The similar isotope composition of Fe plaque and soil, and the similar fractionation magnitude between Fe plaque and the solution and between goethite and the solution, suggested that desorption-sorption between iron oxides and the solution could be important at the soil-soil solution-Fe plaque continuum. This study reveals the roles of chloride and sulfate ions: (i) induce the mobility of light Cd isotopes from soil to the soil solution, (ii) chloro-Cd and sulfato-Cd complexes contribute to Cd immobilization in the Fe plaque and uptake into roots, and (iii) facilitate second leaves/node II-to-grain Cd transport within shoots. These results provide insights into the anion-induced Cd isotope effect in the soil-rice system and the roles of anions in facilitating Cd migration and transformation.

Cd isotope fractionation in a soil-rice system: Roles of pH and mineral transformation during Cd immobilization and migration processes.

Cd speciation in soil and its transport to rice roots are influenced by the soil pH, oxidation-reduction potential, and mineral transformation; however, the immobilization and migration of Cd in soil-rice systems with different pH values under distinct water regimes remain unclear. This study used Cd isotope fractionation, soil physical analysis, and root gene quantification to elucidate the immobilization and transport of Cd in different soil-rice systems. In drainage soils, the high soil pH enhanced the transformation and magnitude of negative fractionation of Cd from MgCl2 extract to FeMn oxide-bound pool; however, it favored Cd uptake and root-to-grain transport. Compared with drainage regimes, the flooding regimes shifted fractionation toward heavy isotopes from MgCl2-extracted Cd to FeMn oxide-bound Cd in acidic soils (∆114/110CdMgCl2 extract - FeMn oxide-bound Cd = -0.09 ± 0.03 ‰) and to light isotopes from MgCl2-extracted Cd to carbonate-bound Cd in neutral and alkaline soils (∆114/110CdMgCl2 extract - carbonate-bound Cd = 0.29-0.40 ‰). The submerged soils facilitated the forming of carbonate and poorly crystalline minerals (such as ferrihydrite), which were transformed into highly crystalline forms (such as goethite). These results demonstrated that the dissolution-precipitation process of iron oxides was essential for controlling soil Cd availability under flooding regimes, and the relative contribution of carbonate minerals to Cd immobilization was promoted by a high soil pH. Flooding regimes induced lower expressions of OsNRAMP1 and OsNRAMP5 to limit the uptake of light Cd isotopes from MgCl2-extract pool, whereas a teeter-totter effect on gene expression patterns in roots (including those of OsHMA3 and OsHMA2) limited the transport of heavy Cd isotopes from root to grain. These findings demonstrate that flooding regimes could exert multiple effects on soil Cd immobilization and Cd transport to grain. Moreover, alkaline soil was conducive to forming carbonate minerals to sequester Cd.

Cadmium isotope fractionation and gene expression evidence for tracking sources of Cd in grains during grain filling in a soil-rice system.

Grain filling is the key period that causes excess cadmium (Cd) accumulation in rice grains. Nevertheless, uncertainties remain in distinguishing the multiple sources of Cd enrichment in grains. To better understand the transport and redistribution of Cd to grains upon drainage and flooding during grain filling, Cd isotope ratios and Cd-related gene expression were investigated in pot experiments. The results showed that the Cd isotopes in rice plants were much lighter than those in soil solutions (∆114/110Cdrice-soil solution = -0.36 to -0.63 ‰) but moderately heavier than those in Fe plaques (∆114/110Cdrice-Fe plaque = 0.13 to 0.24 ‰). Calculations revealed that Fe plaque might serve as the source of Cd in rice (69.2 % to 82.6 %), particularly upon flooding at the grain filling stage (82.6 %). Drainage at the grain filling stage yielded a larger extent of negative fractionation from node I to the flag leaves (∆114/110Cdflag leaves-node I = -0.82 ± 0.03 ‰), rachises (∆114/110Cdrachises-node I = -0.41 ± 0.04 ‰) and husks (∆114/110Cdrachises-node I = -0.30 ± 0.02 ‰), and significantly upregulated the OsLCT1 (phloem loading) and CAL1 (Cd-binding and xylem loading) genes in node I relative to that upon flooding. These results suggest that phloem loading of Cd into grains and transport of Cd-CAL1 complexes to flag leaves, rachises and husks were simultaneously facilitated. Upon flooding of grain filling, the positive fractionation from the leaves, rachises and husks to the grains (∆114/110Cdflag leaves/rachises/husks-node I = 0.21 to 0.29 ‰) is less pronounced than those upon drainage (∆114/110Cdflag leaves/rachises/husks-node I = 0.27 to 0.80 ‰). The CAL1 gene in flag leaves is down-regulated relative to that upon drainage. Thus, the supply of Cd from the leaves, rachises and husks to the grains is facilitated during flooding. These findings demonstrate that the excess Cd was purposefully transported to grain via xylem-to-phloem within nodes I upon the drainage during grain filling, and the expression of genes responsible for encoding ligands and transporters together with isotope fractionation could be used to tracking the source of Cd transported to rice grain.

Long non-coding RNA MSTRG.81401 short hairpin RNA relieves diabetic neuropathic pain and behaviors of depression by inhibiting P2X4 receptor expression in type 2 diabetic rats.

Patients with diabetic neuropathic pain (DNP) experience immense physical and mental suffering, which is comorbid with other mental disorders, including major depressive disorder (MDD). P2X4 receptor, one of the purinergic receptors, is a significant mediator of DNP and MDD. The present study aimed to identify the roles and mechanisms of MSTRG.81401, a long non-coding RNA (lncRNA), in alleviating DNP and MDD-like behaviors in type 2 diabetic rats. After administration with MSTRG.81401 short hairpin RNA (shRNA), the model + MSTRG.81401 shRNA group demonstrated increased mechanical withdrawal threshold, thermal withdrawal latency, open-field test, and sucrose preference test; however, immobility time on the forced swimming test decreased. MSTRG.81401 shRNA administration significantly decreased the expression of the P2X4 receptor, tumor necrosis factor-α, and interleukin-1ß in the hippocampus and spinal cord in the model + MSTRG.81401 shRNA group. Simultaneously, MSTRG.81401 shRNA administration downregulated phosphorylation of ERK1/2 in the hippocampus and spinal cord. Thus, lncRNA MSTRG.81401 shRNA can alleviate DNP and MDD-like behaviors in type 2 diabetic rats and may downregulate the expression of P2X4 receptors in the hippocampus and spinal cord of rats.

Cadmium uptake and transport processes in rice revealed by stable isotope fractionation and Cd-related gene expression.

Multiple processes are involved in Cd transfer in rice plants, including root uptake, xylem loading, and immobilization. These processes can be mediated by membrane transporters and can alter Cd speciation by binding Cd to different organic ligands. However, it remains unclear which processes control Cd transport in rice in response to different watering conditions in soil. Herein, Cd isotope fractionation and Cd-related gene expression were employed to investigate the key regulatory mechanisms during uptake, root-to-shoot, and stem-to-leaf transport of Cd in rice grown in pot experiments with Cd-contaminated soil under flooded and non-flooded conditions, respectively. The results showed that soil flooding decreased the Cd concentration in soil porewater and, thereby, Cd uptake and transport in rice. Cd isotopes fractionated negatively from soil porewater to the whole rice (flooded: ∆114/110Cdrice-porewater = -0.15‰, non-flooded: ∆114/110Cdrice-porewater = -0.39‰), suggesting that Cd transporters preferentially absorbed light Cd isotopes. The non-flooded treatment revealed an upregulated expression of OsNRAMP1 and OsNRAMP5 genes compared to the flooded treatment, which may partially contribute to its more pronounced porewater-to-rice fractionation. Cd isotopes fractionated positively from roots to shoots under flooded conditions (∆114/110Cdshoot-root = 0.19‰). However, a reverse direction of fractionation was observed under non-flooded conditions (∆114/110Cdshoot-root = -0.67‰), which was associated with the substantial upregulation of CAL1 in roots, facilitating xylem loading of Cd-CAL1 complexes with lighter isotopes. After being transported to the shoots, the majority of Cd were detained in stems (44%-55%), which were strongly enriched in lighter isotopes than in the leaves (∆114/110Cdleaf-stem = 0.77 to 1.01‰). Besides the Cd-CAL1 transported from the roots, the expression of OsPCS1 and OsHMA3 in the stems could also favor the enrichment of Cd-PCs with lighter isotopes, leaving heavier isotopes to be transported to the leaves. The higher expression levels of OsMT1e in older leaves than in younger leaves implied that Cd immobilization via binding to metallothioneins like OsMT1e may favor the enrichment of lighter isotopes in older leaves. The non-flooded treatment showed lighter Cd isotopes in younger leaves than the flooded treatment, suggesting that more Cd-CAL1 in the stems and Cd-PCs in the older leaves might be transported to the younger leaves under non-flooded conditions. Our results demonstrate that isotopically light Cd can be preferentially transported from roots to shoots when more Cd is absorbed by rice under non-flooded conditions, and isotope fractionation signature together with gene expression quantification has the potential to provide a better understanding of the key processes regulating Cd transfer in rice.

Water Management Alters Cadmium Isotope Fractionation between Shoots and Nodes/Leaves in a Soil-Rice System.

The drainage of rice soils increases Cd solubility and results in high Cd concentrations in rice grains. However, plant Cd uptake is limited by sorption to iron plaques, and Cd redistribution in the plant is regulated by the nodes. To better understand the interplay of Cd uptake and redistribution in rice under drained and flooded conditions, we determined stable Cd isotope ratios and the expression of genes coding transporters that can transport Cd into the plant cells in a pot experiment. In soil, both water management practices showed similar patterns of isotope variation: the soil solution was enriched in heavy isotopes, and the root Fe plaque was enriched in light isotopes. In rice, the leaves were heavier (Δ114/110Cdleaf-shoot = 0.17 to 0.96‰) and the nodes were moderately lighter (Δ114/110Cdnode-shoot = -0.26 to 0.00‰) relative to the shoots under flooded conditions, indicating preferential retention of light isotopes in nodes and export of heavy isotopes toward leaves. This is generally reversed under drained conditions (Δ114/110Cdleaf-shoot = -0.25 to -0.04‰, Δ114/110Cdnode-shoot = 0.10 to 0.19‰). The drained treatment resulted in significantly higher expression of OsHMA2 and OsLCT1 (phloem loading) but lower expression of OsHMA3 (vacuolar sequestration) in nodes and flag leaves relative to the flooded treatment. It appeared that OsHMA2 and OsLCT1 might preferentially transport isotopically heavier Cd, and the excess Cd was purposefully retranslocated via the phloem under drained conditions when the vacuoles could not retain more Cd. Cd in seeds was isotopically heavier than that in stems under both water management practices, indicating that heavy isotopes were preferentially transferred toward seeds via the phloem, leaving light isotopes retained in stems. These findings demonstrate that the Fe plaque preferentially adsorbs and occludes light Cd isotopes on the root surface, and distinct water management practices alter the gene expression of key transporters in the nodes, which corresponds to a change in isotope fractionation between shoots and nodes/leaves.