Nitrate facilitates cadmium uptake, transport and accumulation in the hyperaccumulator Sedum plumbizincicola
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The aims of this study are to investigate whether and how the nitrogen form (nitrate (NO3 –) versus ammonium (NH4 +)) influences cadmium (Cd) uptake and translocation and subsequent Cd phytoextraction by the hyperaccumulator species Sedum plumbizincicola. Plants were grown hydroponically with N supplied as either NO3 – or NH4 +. Short-term (36 h) Cd uptake and translocation were determined innovatively and quantitatively using a positron-emitting 107Cd tracer and positron-emitting tracer imaging system. The results show that the rates of Cd uptake by roots and transport to the shoots in the NO3 – treatment were more rapid than in the NH4 + treatment. After uptake for 36 h, 5.6 (0.056 μM) and 29.0 % (0.290 μM) of total Cd in the solution was non-absorbable in the NO3 – and NH4 + treatments, respectively. The local velocity of Cd transport was approximately 1.5-fold higher in roots (3.30 cm h−1) and 3.7-fold higher in shoots (10.10 cm h−1) of NO3 –- than NH4 +-fed plants. Autoradiographic analysis of 109Cd reveals that NO3 – nutrition enhanced Cd transportation from the main stem to branches and young leaves. Moreover, NO3 – treatment increased Cd, Ca and K concentrations but inhibited Fe and P in the xylem sap. In a 21-day hydroponic culture, shoot biomass and Cd concentration were 1.51 and 2.63 times higher in NO3 –- than in NH4 +-fed plants. We conclude that compared with NH4 +, NO3 – promoted the major steps in the transport route followed by Cd from solution to shoots in S. plumbizincicola, namely its uptake by roots, xylem loading, root-to-shoot translocation in the xylem and uploading to the leaves. S. plumbizincicola prefers NO3 – nutrition to NH4 + for Cd phytoextraction.
KeywordsAmmonium Cadmium Nitrate Positron-emitting tracer imaging system (PETIS) Sedum plumbizincicola Transport Uptake Xylem sap
This research was supported by the National Natural Science Foundation of China (Projects 40930739, 41201300 and 41230858), by a grant from the Strategic International Cooperative Program, Japanese Science and Technology Agency (JST) and in part by the Japanese Society for the Promotion of Science (Grant-in-Aid for Scientific Research No. 23380155). We thank Mr. H. Suto (Tokyo Nuclear Services Co. Ltd.) and Dr. S. Ishii (Japanese Atomic Energy Agency) for the technical assistance in 107Cd production, and Prof C. X. Tang (La Trobe University, Australia) for helps on experimental design and paper improvement.
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