Effect of Hydroponically Supplied Selenium Forms on Cadmium and Nickel Accumulation in Rice

doi:10.1016/j.rsci.2025.03.005

Abstract

Abstract:

Rice (Oryza sativa L.) farmers face challenges with metal accumulation in grain, with nickel (Ni) recently emerging as a concern due to its potential to exceed legal limits, alongside cadmium (Cd). Information on Ni behaviour and its interaction with Cd remains limited. Selenium (Se) is commonly used for rice biofortification and can reduce the accumulation of toxic metals in plants. Therefore, this study investigates how Ni and Cd influence mutual accumulation in rice and examines the impact of different Se forms on their interactions. Plants were grown hydroponically with various combinations of Cd (5 or 20 μmol/L), Ni (20 μmol/L), and Se (5 μmol/L) as selenate (Se⁶⁺) or selenite (Se⁴⁺) for 7 d. Plant growth, lipid peroxidation, and element accumulation were measured, and the distribution of Se and Ni in tissues was assayed using synchrotron-based µXRF 2D imaging. Cd and Ni were toxic to rice, reducing leaf and root biomass by 40%‒50% and inducing oxidative stress. However, their combined presence did not further exacerbate leaf growth reduction. Cd reduced root Ni accumulation by approximately 50% at equimolar concentrations, likely due to competitive inhibition at shared transport sites. Se promoted root growth in the presence of Ni and low Cd, suggesting an antioxidant role in mitigating metal-induced stress. However, high doses of Ni and Cd together significantly reduced Se accumulation (by 60% and 77% for Se⁴⁺ in roots and Se⁶⁺ in leaves, respectively) and caused severe oxidative stress in the presence of Se⁴⁺. The effectiveness of Se biofortification varied depending on the Se form: Se⁶⁺ was more effective at reducing Ni accumulation, while Se⁴⁺ effectively reduced Cd accumulation (by 45%‒75%) at low concentrations and Ni accumulation in the absence of Cd (by 50%). In conclusion, this study demonstrates that Se can mitigate Cd and Ni accumulation in rice. However, the co-presence of Cd and Ni may compromise Se enrichment in rice, highlighting the complexity of their interactions.

Key words: biofortification, lipid peroxidation, metal mapping, metal transport, µXRF imaging, oxidative stress

Mirko Salinitro, Martino Rabbia, Antony van der Ent, Marco Prati, Dennis Brueckner, Andrea Ertani, Maria Martin, Michela Schiavon. Effect of Hydroponically Supplied Selenium Forms on Cadmium and Nickel Accumulation in Rice[J]. Rice Science, 2025, 32(4): 561-574.

Figures/Tables 7

Fig. 1. Leaf (A) and root (B) dry weights of rice plants. Data were collected after 7 d of hydroponic cultivation with combinations of cadmium (Cd, 5 and 20 μmol/L, Cd5 and Cd20, respectively), nickel (Ni, 20 μmol/L), and selenium (Se, as selenate Se6+ or selenite Se4+, each at 5 μmol/L). CK, Control. Data are mean ± SE (n = 9). Different lowercase letters above bars identify significant differences among treatments after analysis of variance followed by Tukey’s HSD test (P < 0.05).

Fig. 2. Thiobarbituric acid reactive substances (TBARS) as an indictor of lipid peroxidation in hydroponic cultivation rice leaves. Data were collected after 7 d of hydroponic cultivation with combinations of cadmium (Cd, 5 and 20 μmol/L, Cd5 and Cd20, respectively), nickel (Ni, 20 μmol/L), and selenium (Se, as selenate Se6+ or selenite Se4+, each at 5 μmol/L). CK, Control. Data are mean ± SE (n = 3). Different lowercase letters above bars identify significant differences among treatments after analysis of variance followed by Tukey’s HSD test (P < 0.05).

Fig. 3. Cadmium (Cd), nickel (Ni), and selenium (Se) concentrations in leaves and roots of rice plants. A‒C, Cd (A), Ni (B), and Se (C) concentrations in leaves of rice plants. D‒F, Cd (D), Ni (E), and Se (F) concentrations in roots of rice plants. Data were collected after 7 d of hydroponic cultivation with combinations of cadmium (Cd, 5 and 20 μmol/L, Cd5 and Cd20, respectively), nickel (Ni, 20 μmol/L), and selenium (Se, as selenate Se6+ or selenite Se4+, each at 5 μmol/L). CK, Control.

Fig. 4. Translocation factors (TF) of cadmium (Cd, A), nickel (Ni, B), and selenium (Se, C) of rice plants. Data were collected after 7 d of hydroponic cultivation with combinations of cadmium (Cd, 5 and 20 μmol/L, Cd5 and Cd20, respectively), nickel (Ni, 20 μmol/L), and selenium (Se, as selenate Se6+ or selenite Se4+, each at 5 μmol/L). CK, Control.

Fig. 5. Distribution of selenium (Se), nickel (Ni), and iron (Fe) in roots of rice plants treated with Se and Ni. A‒C, Distribution of Se (A), Ni (B), and Fe (C) in roots of rice plants treated with 5 μmol/L Se6+ and 20 μmol/L Ni. D, Tricolor map showing simultaneous distribution of Se (red), Ni (green), and Fe (blue). Scale bars, 0.5 mm.

Fig. 6. Distribution of selenium (Se) and nickel (Ni) in leaves and roots of rice plants treated with 5 μmol/L Se6+ and different concentrations of cadmium (Cd) and Ni. A, C, E, G, I, K, M, and O, Distribution of Se in leaves and roots of rice plants treated with control (A), Se6+ (C), Se6+ and 5 μmol/L Cd (E), Se6+ and 20 μmol/L Cd (G), Ni (I), Se6+ and Ni (K), Se6+, 5 μmol/L Cd, and Ni (M), as well as Se6+, 20 μmol/L Cd, and Ni (O). B, D, F, H, J, L, N, and P, Distribution of Ni in leaves and roots of rice plants treated with control (B), Se6+ (D), Se6+ and 5 μmol/L Cd (F), Se6+ and 20 μmol/L Cd (H), Ni (J), Se6+ and Ni (L), Se6+, 5 μmol/L Cd, and Ni (N), as well as Se6+, 20 μmol/L Cd, and Ni (P). The concentrations used for Se6+ and Ni are 5 and 20 μmol/L, respectively. Scale bars, 5 mm.

Fig. 7. Distribution of selenium (Se) and nickel (Ni) in leaves and roots of rice plants treated with 5 μmol/L Se4+ and different concentrations of cadmium (Cd) and Ni. A, C, E, G, I, K, M, and O, Distribution of Se in leaves and roots of rice plants treated with control (A), Se4+ (C), Se4+ and 5 μmol/L Cd (E), Se4+ and 20 μmol/L Cd (G), Ni (I), Se4+ and Ni (K), Se4+, 5 μmol/L Cd, and Ni (M), as well as Se4+, 20 μmol/L Cd, and Ni (O). B, D, F, H, J, L, N, and P, Distribution of Ni in leaves and roots of rice plants treated with control (B), Se4+ (D), Se4+ and 5 μmol/L Cd (F), Se4+ and 20 μmol/L Cd (H), Ni (J), Se4+ and Ni (L), Se4+, 5 μmol/L Cd, and Ni (N), as well as Se4+, 20 μmol/L Cd, and Ni (P). The concentrations used for Se4+ and Ni are 5 and 20 μmol/L, respectively. Scale bars, 5 mm.

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