Zn/Cd status-dependent accumulation of Zn and Cd in root parts in tobacco is accompanied by specific expression of ZIP genes

Abstract

Background: Root-to-shoot translocation of zinc (Zn) and cadmium (Cd) depends on the concentrations of both metals in the medium. A previous study on tobacco (Nicotiana tabacum) pointed to the contribution of NtZIP1, NtZIP2, NtZIP4 and NtIRT1-like in the regulation of this phenomenon. To learn more, Zn and Cd accumulation, root/ shoot distribution and the expression of ZIP genes were investigated in the apical, middle and basal root parts. Results: We show that Zn/Cd status-dependent root-shoot distribution of both metals was related to distinct metal accumulation in root parts. At low Zn and Cd in the medium, the apical part contained the highest metal level; at higher concentrations, the middle and basal parts were the major sink for excess metal. The above were accompanied by root part-specific expression pattern modifications of ZIPs (NtZIP1-like, NtZIP2, NtZIP4A/B, NtZIP5A/B, NtZIP5-like, NtZIP8, NtZIP11, NtIRT1, and NtIRT1-like) that fell into four categories with respect to the root part. Furthermore, for lower Zn/Cd concentrations changes were noted for NtZIP5A/B and NtZIP5-like only, but at higher Zn and Cd levels for NtZIP1-like, NtZIP5-like, NtZIP8, NtZIP11, NtIRT1, and NtIRT1-like. NtZIP1, here renamed to NtZIP5B, was cloned and characterized. We found that it was a zinc deficiency-inducible transporter involved in zinc and cadmium uptake from the soil solution primarily by the middle root part. Conclusions: We conclude that regulation of the longitudinal distribution of Zn and Cd is highly specific, and that the apical, middle and basal root parts play distinct roles in Zn/Cd status-dependent control of metal translocation efficiency to shoots, including the stimulation of Zn translocation to shoots in the presence of Cd. These results provide new insight into the root part-specific unique role of NtZIP5B and other ZIP genes in the longitudinal distribution of zinc and cadmium and their contribution to the regulation of root-to-shoot translocation.

Cell Viability and Immune Response to Low Concentrations of Nickel and Cadmium: An In Vitro Model

“…Cd enters cells through the ZIP (ZRT, IRT-like protein) transporter, metallothionein, and DMT1 (divalent metal transporter-1). Once in the cell, Cd exhibits cytotoxicity by inhibiting the DNA repair process, cell proliferation and tumor suppressor functions, and causing oxidative stress [ 18 , 19 , 20 , 21 ]. Additionally, Cd inactivates the p53 tumor suppressor protein, which is important for cell cycle arrest and apoptosis regulation, thereby inducing DNA damage and inhibiting DNA repair [ 22 ].…”

“…Our results showed that 50 nM of Ni and 10 nM of Cd alone did not have a significant effect on cell viability; however, when the two heavy metals were used in mixture at these concentrations, cell viability was significantly lower than that of the control group after 48 h. Studies on the synergic [ 23 , 24 ] and antagonistic [ 25 , 26 ] effects of heavy metal co-exposure have been conducted, and their results suggest that the mixed exposure of Ni and Cd has a synergic effect on cell viability. Differences in cell entry and cytotoxic mechanisms of Ni and Cd [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ] have been identified; therefore, their individual properties may be related to these synergic effects.…”

Suppression of NtZIP4A/B Changes Zn and Cd Root-to-Shoot Translocation in a Zn/Cd Status-Dependent Manner

“…Furthermore, Zn translocation depends on the presence of other metals in the medium, including Cd. Inhibition of translocation has often been described [26][27][28]; however, our recent study showed stimulation in the presence of certain Cd concentrations [28,29]. An increase in Zn translocation was found in the presence of 0.25 and 1 µM Cd in plants grown at low/medium Zn concentrations (0 to 1 µM).…”

“…Of the ZIP genes tested in tobacco, only one, NtZIP4A/B, upregulated by Zn deficiency, showed similar transcript levels in all parts of the root at tested combinations of Zn/Cd concentrations [28]. There are two copies of NtZIP4, NtZIP4A, and NtZIP4B (sharing 97.57% homology at the amino acid level) with the same expression pattern in tobacco [31].…”

“…Their different capacities to accumulate both metals that depended on Zn/Cd status were revealed, and the middle and basal parts were suggested to play a role of a sink for excess Zn/Cd in the medium. Moreover, of the nine ZIP genes (Zrt Irt-like Proteins); [30] tested, for eight (NtZIP1-like, NtZIP2, NtZIP4A/B, NtZIP5A/B, NtZIP5-like, NtZIP8, NtZIP11, NtIRT1, and NtIRT1-like), the expression pattern was specific to the root part [28]. Altogether, these results were the first to indicate the distinct role of the root parts in the regulation of Zn/Cd status-dependent translocation efficiency.…”