Key Laboratory of Original Agro-Environmental Pollution Prevention and Control, Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, PR China, Tianjin 300191, China.
Key Laboratory of Original Agro-Environmental Pollution Prevention and Control, Agro-Environmental Protection Institute, Ministry of Agriculture and Rural Affairs, PR China, Tianjin 300191, China.
Environ Pollut. 2020 Jul;262:114236. doi: 10.1016/j.envpol.2020.114236. Epub 2020 Feb 26.
The accumulation of cadmium (Cd) in rice grains is closely associated with the content of mineral nutrients and amino acid metabolism, but the causal link among them is unclear. Profiles of amino acids (AAs) and quantities of essential nutrients in grains from early and late rice cultivars grown at four sites with different Cd levels were analyzed in the present study. Hazard quotients (HQs) for consumers by intake of rice from late cultivars were much higher than that from early cultivars at sites with soil Cd content of 0.25, 0.61 and 0.84 mg kg. Cadmium accumulation in grains resulted in a sharp reduction of total essential AAs and non-essential AAs in both early and late rice cultivars. High-Cd-accumulating (HCA) cultivars had significantly higher level of glutamate (Glu) than low-Cd-accumulating (LCA) cultivars when rice Cd content was less than 0.20 mg kg. However, Glu level in grains dramatically declined with the accumulation of Cd, which subsequently leaded to the reduction of other AAs. Cadmium content was well predicted by five amino acids (i.e., Glu, Alanine, Phenylalanine, Glycine and Threonine) or four essential elements (Ca, Fe, Mn and Zn) when rice Cd was less than 0.80 mg kg. Amino acids played more important roles than nutrients in Cd accumulation. When Cd content was in the range of 0.40-1.16 mg kg, the Mn content in rice increased significantly with the increase of Cd content, while the Glu content dropped down synchronously. Remarkably, the ratio between Mn and Glu displayed the highest direct path coefficient on Cd accumulation than any single cation or amino acid. These results indicate that high capacity in synthesizing Glu and concentrating Mn is the determinant factor for Cd accumulation in rice grains, and abundant Glu in aleurone layer may alleviate Cd toxicity by forming Glu-Cd complex.
稻米中镉的积累与矿物质营养和氨基酸代谢密切相关，但它们之间的因果关系尚不清楚。本研究分析了在镉含量不同的四个地点种植的早稻和晚稻品种的籽粒中氨基酸（AA）谱和必需营养元素的含量。在土壤镉含量为 0.25、0.61 和 0.84mg/kg 的地点，晚稻品种稻米镉含量对消费者的危害系数（HQ）远高于早稻品种。镉在谷物中的积累导致早稻和晚稻品种的必需和非必需总氨基酸含量急剧减少。当稻米镉含量低于 0.20mg/kg 时，高镉积累（HCA）品种的谷氨酸（Glu）水平明显高于低镉积累（LCA）品种。然而，随着镉的积累，谷粒中的 Glu 水平急剧下降，继而导致其他 AA 的减少。当稻米镉含量低于 0.80mg/kg 时，镉含量可以很好地由五种氨基酸（即谷氨酸、丙氨酸、苯丙氨酸、甘氨酸和苏氨酸）或四种必需元素（钙、铁、锰和锌）来预测。当镉含量在 0.40-1.16mg/kg 范围内时，随着镉含量的增加，稻米中锰的含量显著增加，而 Glu 含量同步下降。值得注意的是，Mn 与 Glu 之间的比值对 Cd 积累的直接路径系数高于任何单个阳离子或氨基酸。这些结果表明，在水稻籽粒中积累 Cd 的决定因素是合成 Glu 和浓缩 Mn 的能力高，糊粉层中丰富的 Glu 可能通过形成 Glu-Cd 复合物来减轻 Cd 毒性。
