Abstract
BackgroundRoot-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.ResultsWe 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.ConclusionsWe 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.
Highlights
Root-to-shoot translocation of zinc (Zn) and cadmium (Cd) depends on the concentrations of both metals in the medium
Detailed bioinformatics analysis showed that NtZIP5A has a nucleotide sequence identical with NtZIP1 previously identified by Sano et al [31], and here we provided data based on which NtZIP1 was renamed NtZIP5A
In the same location we found Zinc deficiency-related element (ZDRE) elements, IDE2, Abscisic acid-responsive element (ABRE) and ABRE4, MYB-like sequence (MYB binding region from A. thaliana), Box 4 and GT1, STRE (Stress Response Element) for heat, osmotic, low pH and nutrient starvation, and CAAT-box, whereas lightresponsive G-box was detected in a different location [33,34,35,36,37]
Summary
Root-to-shoot translocation of zinc (Zn) and cadmium (Cd) depends on the concentrations of both metals in the medium. Zn and Cd accumulation, root/ shoot distribution and the expression of ZIP genes were investigated in the apical, middle and basal root parts. Tobacco is known to accumulate metals (including Zn and Cd) in aerial parts more efficiently than many other species [1, 2]. It has, been frequently used for phytoextraction purposes [3, 4]. It is based on one metal transport gene being regulated by more than one metal, and on metal
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