title: Nitrate facilitates cadmium uptake, transport and accumulation in the hyperaccumulator Sedum plumbizincicola.
abstract: 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 (107)Cd 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 (109)Cd 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.
authors.affiliation: Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China.
authors.forename: Pengjie
authors.initials: P
authors.lastname: Hu
authors.forename: Yong-Gen
authors.initials: YG
authors.lastname: Yin
authors.forename: Satoru
authors.initials: S
authors.lastname: Ishikawa
authors.forename: Nobuo
authors.initials: N
authors.lastname: Suzui
authors.forename: Naoki
authors.initials: N
authors.lastname: Kawachi
authors.forename: Shu
authors.initials: S
authors.lastname: Fujimaki
authors.forename: Masato
authors.initials: M
authors.lastname: Igura
authors.forename: Cheng
authors.initials: C
authors.lastname: Yuan
authors.forename: Jiexue
authors.initials: J
authors.lastname: Huang
authors.forename: Zhu
authors.initials: Z
authors.lastname: Li
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Makino
authors.forename: Yongming
authors.initials: Y
authors.lastname: Luo
authors.forename: Peter
authors.initials: P
authors.lastname: Christie
authors.forename: Longhua
authors.initials: L
authors.lastname: Wu
mesh_terms: D001673:Biodegradation, Environmental; D001692:Biological Transport / Q000502:physiology; D002104:Cadmium / Q000737:chemistry / Q000378:metabolism*; D005308:Fertilizers; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism*; D018517:Plant Roots; D018520:Plant Shoots; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000378:metabolism; D031963:Sedum / Q000378:metabolism*
chemical_list: D005308:Fertilizers; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D002104:Cadmium