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Contrasting effects of nicotianamine synthase knockdown on zinc and nickel tolerance and accumulation in the zinc/cadmium hyperaccumulator A rabidopsis halleri
Author(s) -
Cornu JeanYves,
Deinlein Ulrich,
Höreth Stephan,
Braun Manuel,
Schmidt Holger,
Weber Michael,
Persson Daniel P.,
Husted Søren,
Schjoerring Jan K.,
Clemens Stephan
Publication year - 2015
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.13237
Subject(s) - xylem , hyperaccumulator , chemistry , zinc , shoot , cadmium , botany , environmental chemistry , phytoremediation , biochemistry , biology , heavy metals , organic chemistry
Summary Elevated nicotianamine synthesis in roots of A rabidopsis halleri has been established as a zinc (Zn) hyperaccumulation factor. The main objective of this study was to elucidate the mechanism of nicotianamine‐dependent root‐to‐shoot translocation of metals. Metal tolerance and accumulation in wild‐type ( WT ) and Ah NAS 2 ‐ RNA interference ( RNA i) plants were analysed. Xylem exudates were subjected to speciation analysis and metabolite profiling. Suppression of root nicotianamine synthesis had no effect on Zn and cadmium (Cd) tolerance but rendered plants nickel (Ni)‐hypersensitive. It also led to a reduction of Zn root‐to‐shoot translocation, yet had the opposite effect on Ni mobility, even though both metals form coordination complexes of similar stability with nicotianamine. Xylem Zn concentrations were positively, yet nonstoichiometrically, correlated with nicotianamine concentrations. Two fractions containing Zn coordination complexes were detected in WT xylem. One of them was strongly reduced in Ah NAS 2 ‐suppressed plants and coeluted with 67 Zn‐labelled organic acid complexes. Organic acid concentrations were not responsive to nicotianamine concentrations and sufficiently high to account for complexing the coordinated Zn. We propose a key role for nicotianamine in controlling the efficiency of Zn xylem loading and thereby the formation of Zn coordination complexes with organic acids, which are the main Zn ligands in the xylem but are not rate‐limiting for Zn translocation.