In plants, Cd causes perturbation of root metal uptake and is known to interfere with
the metal translocation to the shoot. The most significant effect is the strongly
reduced transport of Fe. Fe accumulation in roots under Cd stress revealed that it
is not the Fe acquisition but the Fe loading to xylem elements that is blocked by
Cd, which can be a result of competition between Fe and Cd for the transporters. However,
in animal cells as well as in plant stomata guard cells, Cd was shown to move through
Ca channels. To clarify whether the perturbation of metal translocation/xylem loading
caused by Cd show any regularity, translocation ability was tested by the determination
of the metal content in leaves of hydroponically cultured (1/4 Hoagland nutrient solution,
Fe source: 10 mu M Fe-(III)-citrate) poplar plants grown for three weeks with or without
10 mu M Cd(NO3)(2) treatment. Metals could be classified into two groups according
to the behavior of their translocation under Cd treatment: alkaline earth metals (except
Mg), Zn and Mn were influenced similarly to Ca, but other transition metals (together
with alkali metals and Al) behaved like the Fe. Based on the translocation pattern,
Cd seems to inhibit the transport of Ca-like metals competitively, but a different
type of inhibition is exerted on the transition metal transport, with which Cd can
share a common translocation system. The strongly decreased translocation of chelator-dependent
transition metals may indicate Cd related disturbances in signalling pathways and
gene expression of xylem transporters or chelators. (C) 2011 Elsevier Masson SAS.
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