National Natural Science Foundation of China (No. 41771343) and the Science and Technology Planning Project of Guangdong Province (No. 2016A020221013, No.2014A050503032)
Rare earth elements (REEs), which are important strategic resources in the world, play an important role in modern high-tech industries and agricultural production. With the demand for REEs increasing steadily day by day, exploitation of rare earth mines is intensifying nowadays. The mining of REEs also produces large volumes of tailings that occupy large tracts of land and pollute farmlands, thus posing potential threat to the local environment and health of the local residents. Phytomining refers to the practice of growing metal-hyperaccumulating plants in metal-polluted land and harvesting the aboveground biomass of the plants to recover metals, while restoring vegetation and remedying polluted soil. So it is an in-situ, low-cost and potentially profitable means of soil remediation. The study on mechanism of metal accumulation and translocation in hyperaccumulators is the fundament for realizing phytomining. However, the studies on hyperaccumulators of nickel, zinc, and arsenic aside, little has been reported on mechanisms of REEs hyperaccumulation. In this study, a review is presented of advancement in the researches both at home and abroad on mechanisms of the four key processes of REEs accumulation, translocation, distribution and detoxification and their relationships with REE fractionation in the soil-plant system, and a conceptual model brought forth of REEs fractionation in hyperaccumulators. Roots of the plants absorb mainly REEs of free ion form, whereas types and concentrations of organic ligands, pH, organic matter and ion diffusion in rhizosphere soil solution would reduce or increase bioavailability of the REEs in soil solution through complexation, adsorption, desorption and precipitation, which in turn affects REEs accumulation and fractionation of the hyperaccumulators. REEs absorption by roots involves both apoplast and symplast pathways, of which the latter include transmembrane transport systems such as Ca ion channel diffusion and Al transport protein. Because of the variation of absorption pathways, Dicranopteris dicthotoma tends to enrich light REEs (LREEs) whereas Phytolacca americana L. does LREEs, but not so intensively. Once absorbed, REEs are further transported upwards along the xylem. As D. dicthotoma is relatively weak in compartmentalization of REEs in the roots, more LREEs in the form of free ions in the xylem move upwards along with transpiration flow into shoots. On the contrary, in the xylem of P. americana heavy REEs (HREEs) are more likely to get complexed with organic acids and move upwards into shoots, especially citric acid, which plays an important role in REEs long-distance transport in xylem. In the end, large amounts of REEs are stored in leaves of the hyperaccumulators. Most of LREEs in the leaves of D. dicthotoma are absorbed by cell walls and stored in apoplasts or deloaded into vacuoles, or may also enter into the cells and get complexed with proteins and chlorophyll for detoxification. The detoxification mechanisms of REEs in the leaves of P. americana are still unclear. It is presumed that P. americana may have its own function of compartmentalization,in detoxifying HREEs and hence enriches HREEs in its leaves.
陈莺燕,刘文深,袁 鸣,郭美娜,刘 畅,Hermine Huot,汤叶涛,仇荣亮.超富集植物对稀土元素吸收转运解毒与分异的研究进展[J].土壤学报,2019,56(4):785-795. DOI:10.11766/trxb201806290190 CHEN Yingyan, LIU Wenshen, YUAN Ming, GUO Meina, LIU Chang, Hermine Huot, TAO Yetao, QIU Rongliang. Advancement in Researches on the Absorption, Translocation, Detoxification and Fractionation of Rare Earth Elements in Hyperaccumulators[J]. Acta Pedologica Sinica,2019,56(4):785-795.复制