title: Kinetic Analysis of Zinc/Cadmium Reciprocal Competitions Suggests a Possible Zn-Insensitive Pathway for Root-to-Shoot Cadmium Translocation in Rice.
abstract: BACKGROUND
  Among cereals, rice has a genetic propensity to accumulate high levels of cadmium (Cd) in grains. Xylem-mediated root-to-shoot translocation rather than root uptake has been suggested as the main physiological factor accounting for the genotypic variation observed in Cd accumulation in shoots and grains. Several evidence indicate OsHMA2 - a putative zinc (Zn) transporter - as the main candidate protein that could be involved in mediating Cd- and Zn-xylem loading in rice. However, the specific interactions between Zn and Cd in rice often appear anomalous if compared to those observed in other staple crops, suggesting that root-to-shoot Cd translocation process could be more complex than previously thought. In this study we performed a complete set of competition experiments with Zn and Cd in order to analyze their possible interactions and reciprocal effects at the root-to-shoot translocation level.
  
  
  RESULTS
  The competition analysis revealed the lack of a full reciprocity when considering the effect of Cd on Zn accumulation, and vice versa, since the accumulation of Zn in the shoots was progressively inhibited by Cd increases, whereas that of Cd was only partially impaired by Zn. Such behaviors were probably dependent on Cd-xylem loading mechanisms, as suggested by: i) the analysis of Zn and Cd content in the xylem sap performed in relation to the concentration of the two metals in the mobile fractions of the roots; ii) the analysis of the systemic movement of (107)Cd in short term experiments performed using a positron-emitting tracer imaging system (PETIS).
  
  
  CONCLUSIONS
  Our results suggest that at least two pathways may mediate root-to-shoot Cd translocation in rice. The former could involve OsHMA2 as Zn(2+)/Cd(2+) xylem loader, whereas the latter appears to involve a Zn-insensitive system that still needs to be identified.
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Fontanili
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy.|Istituto di Biologia e Biotecnologia Agraria (IBBA), Consiglio Nazionale delle Ricerche, 20133, Milan, Italy.
authors.forename: Clarissa
authors.initials: C
authors.lastname: Lancilli
authors.affiliation: Department of Radiation-Applied Biology, Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Suzui
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy.
authors.forename: Bianca
authors.initials: B
authors.lastname: Dendena
authors.affiliation: Department of Radiation-Applied Biology, Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan.
authors.forename: Yong-Gen
authors.initials: YG
authors.lastname: Yin
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Ferri
authors.affiliation: Department of Radiation-Applied Biology, Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Ishii
authors.affiliation: Department of Radiation-Applied Biology, Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kawachi
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Lucchini
authors.affiliation: Department of Radiation-Applied Biology, Takasaki Advanced Radiation Research Institute, Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma, 370-1292, Japan.
authors.forename: Shu
authors.initials: S
authors.lastname: Fujimaki
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy.
authors.forename: Gian Attilio
authors.initials: GA
authors.lastname: Sacchi
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali - Produzione, Territorio, Agroenergia (DISAA), Università degli Studi di Milano, 20133, Milan, Italy. fabio.nocito@unimi.it.
authors.forename: Fabio Francesco
authors.initials: FF
authors.lastname: Nocito
keywords: Cadmium; PETIS; Rice; Translocation; Zinc