Cd affects the translocation of some metals either Fe-like or Ca-like way in poplar

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 (¼ Hoagland nutrient solution, Fe source: 10 μM Fe((III))-citrate) poplar plants grown for three weeks with or without 10 μM 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.