Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 806, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.scitotenv.2021.150633
Keywords
Rice(Oryzasativa); Pathway; Transporter; CAL1; Stem-to-leaf transport; Jointing stage
Categories
Funding
- National Natural Science Foundation of China [420307020, 41877043]
- Guangdong Key Research and Development Project [2019B110207002]
- Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program [2017BT01Z176]
- Guangdong Natural Science Funds for Distinguished Young Scholars [2017A030306010]
- Guangdong Special Support Plan for High-Level Talents [2017TQ04Z511]
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The study found that flooding reduced the concentration of Cd in soil porewater, leading to a decrease in Cd uptake and transport in rice. Under non-flooded conditions, there was an upregulation of OsNRAMP1 and OsNRAMP5 genes, contributing to a more pronounced porewater-to-rice fractionation.
Multiple processes are involved in Cd transfer in rice plants, including root uptake, xylem loading, and immobi-lization. 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, re-spectively. 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: Delta Cd-114/110(rice-porewater) = -0.15%0, non-flooded: Delta Cd-114/110(rice-porewater) = -0.39%0), 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 contrib-ute to its more pronounced porewater-to-rice fractionation. Cd isotopes fractionated positively from roots to shoots under flooded conditions (Delta 114/110Cdshoot-root = 0.19%0). However, a reverse direction of fractionation was observed under non-flooded conditions (Delta Cd-114/110(shoot-root) = -0.67%0), 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 (Delta Cd-114/110(leaf-stem) = 0.77 to 1.01 parts per thousand). 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 CdCAL1 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. (C) 2021 Published by Elsevier B.V.
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