First published online January 23, 2003; 10.1104/pp102.010686
Plant Physiol, February 2003, Vol. 131, pp. 716-724
The Role of Free Histidine in Xylem Loading of Nickel in
Alyssum lesbiacum and Brassica
juncea1
Loubna
Kerkeb2 and
Ute
Krämer*
Max Planck Institute of Molecular Plant Physiology, Am
Mühlenberg 1, D-14476 Golm, Germany
Exposure of the hyperaccumulator Alyssum
lesbiacum to nickel (Ni) is known to result in a dose-dependent
increase in xylem sap concentrations of Ni and the chelator free
histidine (His). Addition of equimolar concentrations of exogenous
L-His to an Ni-amended hydroponic rooting medium enhances
Ni flux into the xylem in the nonaccumulator Alyssum
montanum, and, as reported here, in Brassica
juncea L. cv Vitasso. In B. juncea, reducing the
entry of L-His into the root by supplying D-His
instead of L-His, or L-His in the presence of a
10-fold excess of L-alanine, did not affect root Ni uptake,
but reduced Ni release into the xylem. Compared with B.
juncea, root His concentrations were constitutively about
4.4-fold higher in A. lesbiacum, and did not increase
within 9 h of exposure to Ni. Cycloheximide did not affect root
His or Ni concentrations, but strongly decreased the release of His and Ni from the root into the xylem of A. lesbiacum, whereas
xylem sap concentrations of Ca and Mg remained unaffected.
Near-quantitative chelation of Ni with nitrilotriacetate in the rooting
medium did not enhance Ni flux into the xylem of A.
lesbiacum and B. juncea, suggesting the absence
of a significant apoplastic pathway for Ni entry into the xylem. The
data suggest that in B. juncea roots, Ni2+
uptake is independent of simultaneous uptake of His. In both species,
enhanced release of Ni into the xylem is associated with concurrent
release of His from an increased root free His pool.
1
This work was supported by the German Federal
Ministry of Education and Research (Biofuture Grant no. 031877 to U.K.)
and by the Max Planck Institute of Molecular Plant Physiology (to L.K.).
2
Present address: Department of Biological Sciences,
Coker Life Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208.
*
Corresponding author; e-mail kraemer{at}mpimp-golm.mpg.de; fax
49-331-567898357.
© 2003 American Society of Plant Biologists
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