Histidine-Mediated Nickel and Zinc Translocation in Arabidopsis thaliana and Lepidium ruderale

In this work, the effect of exogenous histidine supply on zinc (Zn) and nickel (Ni) translocation in shoot-excised root systems of the non-accumulating species Arabidopsis thaliana (L.) Heynh. and Lepidium ruderale L. was studied. Intact 7-week-old plants of A. thaliana and L. ruderale were pretreated for 4 h (13:00 till 17:00) with MES/KOH buffered 1 mM L-histidine, L-alanine or demineralized water. After the pretreatment, the leaf rosettes were cut off with a razor blade and the root systems were transferred to a fresh nutrient solution amended with 25 µM Ni(NO3)2 or Zn(NO3)2. Root pressure exudates were collected overnight (till 11:00 AM). The Ni and Zn concentrations in the roots and root pressure exudates were determined by atomic absorption spectrophotometry. The amount of Ni or Zn loaded into the xylem exudate (‘total amount of Ni or Zn exudated’) was calculated as the product of the metal concentration and the volume of root pressure exudate, expressed on a root dry weight basis. The ‘total Zn or Ni amount’ present in the root system and the root pressure exudate together (‘total uptake’), at the end of the experiment, was calculated as the sum of the total amount of Zn or Ni present in the root pressure exudates and the remaining amount in the root system after sap collection, and expressed on a root dry weight basis. Zn or Ni xylem loading was then recalculated as a percentage of the total Zn or Ni uptake. Pretreatment with L-histidine caused a significant increase in the xylem loading and the total amount of exudated Ni and Zn in L. ruderale and Zn in A. thaliana. No increase in Ni xylem loading, Ni concentration in the root pressure exudate, or total amount of Ni exudated was observed in A. thaliana after pretreatment with L-histidine. No decrease in the volume of root pressure exudates was observed in histidine-pretreated plants, indicating that the increase in metal concentration in the root pressure exudates is certainly not attributable to decreased root pressure exudation in any of the treatments. In contrast to L-histidine, pretreatment with L-alanine did not increase the metal concentrations in the root pressure exudates or the percentage of metal loaded into the xylem. The total uptake of Ni and Zn in A. thaliana was significantly higher than in L. ruderale, which is consistent with the higher concentrations of both metals in the roots of A. thaliana. Exogenous L-histidine and L-alanine did not affect the uptake of metals and their concentration in the roots, except for a slight increase in the uptake of Zn and its concentration in the roots of alanine-pretreated A. thaliana. It is concluded that Ni and Zn translocation in L. ruderale and Zn translocation in A. thaliana may be limited by the concentration of free histidine in their roots

Correlated Variation of the Zn Accumulation and Tolerance Capacities among Populations and Ecotypes of the Zn Hyperaccumulator, Noccaea caerulescens

In this work, a comparative analysis of zinc (Zn) accumulation by the excluder Microthlaspi perfoliatum (L.) F.K. Mey, the hyperaccumulator Noccaea japonicum (H. Boissieu) F.K. Mey from ultramafic (serpentine) soil and plants from 19 populations of the hyperaccumulator Noccaea caerulescens F.K. Mey originating from ultramafic, calamine and non-metalliferous soils was carried out. The seedlings were grown for 2 weeks on half-strength Hoagland’s solution at 2 μM ZnSO4, followed by incubation for 6 weeks at 5 μM ZnSO4 (these Zn concentrations were non-toxic for all the populations of all species). The Zn concentration in the roots and shoots was determined by atomic absorption spectrophotometry. In M. perfoliatum, the Zn concentration in the roots was significantly higher than in the shoots, whereas in the hyperaccumulators, N. japonicum and N. caerulescens, the Zn concentrations in both organs were in most cases similar or higher in the shoots. Within N. caerulescens the greatest differences in Zn accumulation in roots and shoots were found among the calamine populations whereas the smallest differences were found among the ultramafic populations. Zn accumulation in roots per unit dry weight decreased in the following order: Les Avinières ≈ St-Baudille ≈ Viviez ≈ Le Coulet ≈ Le Puy de Wolf > Cira > Puente Basadre > Moravskoslezské ≈ Monte Prinzera > St‑Fé-lix-de-Pallières ≈ Prémanon > La Calamine > Le Bleymard > Krušné Hory ≈ Kuopio > Prayon > Wilwerwiltz ≈ Jean Arsac ≈ Plombières. The value of the translocation factor (TF) was the lowest in the excluder M. perfoliatum. In N. japonicum, TF did not significantly differ from the ultramafic populations of N. caerulescens. Among populations of N. caerulescens, the mean TF values varied to a large extent. The highest TF value (5.83) was obtained for Prayon and the lowest value (0.37) for Les Avinières, both belonging to the calamine ecotype. No correlation was found between the Zn concentration in the roots and the Zn concentration in the shoots in N. caerulescens. A significant negative correlation was found between the Zn accumulation in the roots and plant Zn tolerance estimated by the root growth test, which indicates that root Zn tolerance in N. caerulescens might depend, to some extent, on the capacity to restrict the accumulation of Zn in the root, mainly through restricting its uptake into the root. The difference in root Zn tolerance between the calamine and non-metallicolous ecotypes seems to be largely explained by an enhanced Zn sequestration capacity in the calamine ecotype, compared to the non-metallicolous one

Nickel Tolerance and Accumulation Capacities in Different Populations of the Hyperaccumulator Noccaea caerulescens

Abstract: A comparative analysis of nickel (Ni) accumulation by the hyperaccumulator Noccaea japonica (H. Boissieu) F.K. Mey originating from ultramafic (serpentine) soil and plants from 16 populations of the hyperaccumulator Noccaea caerulescens F.K. Mey originating from ultramafic (serpentine), calamine and non-metalliferous soils, was performed. The plants were grown for 2 weeks in half-strength Hoagland’s solution without Ni, followed by a 6-week exposure to NiSO4 at a non-toxic concentration (1 μM). The Ni concentration in the roots and shoots was determined by atomic absorption spectrophotometry. In N. japonica, the Ni concentration in the shoots was significantly lower than in the roots, and lower than that in the shoots of N. caerulescens from the ultramafic populations. The ability of plants from different populations of N. caerulescens to accumulate Ni in roots (per unit dry weight) decreased in the following order: Puente Basadre ≈ Le Coulet > St-Baudille ≈ Cira ≈ Prémanon > Viviez ≈ Monte Prinzera > Les Avinières > Moravskoslezké > Le Bleymard ≈ Krušné Hory ≈ Wilwerwiltz ≈ La Calamine ≈ St-Félix-de-Palliéres ≈ Kuopio > Prayon. The value of the translocation factor in N. japonica did not significantly differ from that in the ultramafic population Puente Basadre of N. caerulescens, whereas it varied within wide limits among the N. caerulescens populations. The highest Ni translocation factor was obtained for the population Monte Prinzera from the ultramafic group and the populations Krušné Hory and Kuopio from the non-metallicolous group, whereas the lowest values were obtained for the calamine populations La Calamine and Prayon. In N. caerulescens, the Ni concentration in the roots was uncorrelated with the Ni concentration in the shoots, but significantly positively correlated with Ni tolerance. The high Ni tolerance in ultramafic populations is apparently explained by a high capacity to sequester Ni in the roots themselves, and not directly related to the root-to-shoot translocation capacity

Cadmium tolerance and accumulation in Excluder Thlaspi arvense and various accessions of hyperaccumulator Noccaea caerulescens

Cadmium (Cd) accumulation and tolerance were analyzed in hyperaccumulator Noccaea caerulescens F.K. Mey and excluder Thlaspi arvense L. Five accessions of N. caerulescens (La Calamine (LC, Belgium), Saint Félix de Palliéres (SF, France), Col du Mas de l’Aire (CMA, France), Ganges (GA, France) from metalliferous soils and Lellingen (LE, Luxembourg) from nonmetalliferous soils) were grown in halfstrength Hoagland solution for 8 weeks in the presence of 1, 5, 25, and 50 μM Cd(N

Histidine promotes the loading of nickel and zinc, but not of cadmium, into the xylem in Noccaea caerulescens.

Histidine is known to be involved in Ni hyperaccumulation. Recently, histidine-dependent xylem loading of Ni and Zn has been demonstrated in the Zn/ Ni/Cd hyperaccumulator, Noccaea caerulescens. Here we tested the hypothesis whether Cd xylem loading is histidinedependent, too. In contrast to that of Ni and Zn, the xylem loading of Cd was not affected by exogenous histidine. Histidine accumulation in root cells appears to facilitate the radial transport of Ni and Zn, but not Cd, across the roots. This may be due to the relatively high preference of Cd for coordination with sulfur over coordination with nitrogen, in comparison with Ni and Zn

Histidine-Mediated Nickel and Zinc Translocation in Intact Plants of the Hyperaccumulator Noccaea caerulescens

In this work, the effect of exogenous histidine supply on zinc (Zn) and nickel (Ni) translocation to the shoots in intact plants of the hyperaccumulator Noccaea caerulescens F.K. Mey was studied. Three series of experiments were carried out. (1) Intact N. caerulescens plants (St-Félix-de-Pallières population) were pretreated for 4 h (12:00 till 16:00) with a MES/KOH-buffered 1 mM L-histidine solution or demineralized water, then exposed overnight (20 h) to 5, 25 or 250 µM Ni or Zn and harvested. (2) Intact N. caerulescens plants of the same population were pretreated with 1 mM L-histidine solution or demineralized water overnight (20 h) and then exposed to 250 µM Ni or Zn for 8 h during the day (10:00 till 18:00) and harvested. (3) Intact N. caerulescens plants (the calamine populations St-Félix-de-Pallières (SF) and La Calamine (LC), and the ultramafic population Monte Prinzera (MP)) were exposed for 8 h (10:00 till 18:00) to 250 µM Ni or Zn and then to 1 mM L-histidine solution or demineralized water overnight (20 h) and harvested. The Ni and Zn concentrations in the roots and shoots were determined by atomic absorption spectrophotometry. The translocation factor (TF), expressed as the shoot to root metal concentration ratio, the total plant Ni or Zn content, and the percentage of the total Ni or Zn content present in the shoot (% translocated) were calculated. A 4 h pretreatment with L-histidine during the afternoon (before metal exposure overnight) significantly decreased the Ni and Zn concentrations in the root and increased the concentration of Ni, but not of Zn, in the shoot, significantly increased both TF and the % translocated for both metals, albeit much more strongly for Ni, and also slightly, but significantly, increased the total plant content of Ni, but not of Zn. Overnight pretreatment with L-histidine (followed by metal exposure during the day) of the same population (SF) had basically similar effects on Ni translocation, but significantly decreased the plant total Ni content, and was without significant effects on Zn translocation, but considerably decreased the root Zn concentration. The different populations under study (SF, MP, LC) showed significant differences in their Ni and Zn uptake and translocation capacities, but in general showed qualitatively similar responses to post-treatment with L‑histidine that strongly increased the TF and the % translocated for both metals in SF and MP, whereas in LC the effect was prominent only for Ni. Significant population × histidine treatment effect interactions were obtained for the root Zn concentration, and the TF and % translocated for Ni, which were largely explained by a relatively low responsiveness to the L-histidine treatment in LC, compared to SF and/or MP. It is concluded that the high endogenous L-histidine concentrations in N. caerulescens are probably functional in the hyperaccumulation of both Ni and Zn. The overall stronger effect of exogenous L-histidine supply on the translocation of Ni, compared to Zn, seems to result, at least in part, from the high Zn burdens at the start of the treatments, particularly in the shoots, which largely mask the apparent effects of exogenous L-histidine supply on the shoot Zn concentration and, to a lower degree, the % Zn translocated

Histidine-mediated xylem loading of zinc is a species-wide character in Noccaea caerulescens.

Histidine plays a crucial role in nickel (Ni) translocation in Ni-hyperaccumulating plants. Here, we investigated its role in zinc (Zn) translocation in four accessions of the Zn hyperaccumulator, Noccaea caerulescens, using the related non-hyperaccumulator, Thlaspi arvense, as a reference. We compared the effects of exogenous histidine supply on Zn xylem loading, and of Zn-histidine complex formation on Zn uptake in energized tonoplast vesicles. The Zn distribution patterns over root tissues were also compared. Exogenous histidine supply enhanced Zn xylem loading in all the N. caerulescens accessions, but decreased it in T. arvense. Zn distribution patterns over root tissues were similar, apart from the accumulation in cortical and endodermal cells, which was much lower in N. caerulescens than in T. arvense. Zn uptake in energized tonoplast vesicles was inhibited significantly in N. caerulescens, but not affected significantly in T. arvense, when Zn was supplied in combination with histidine in a 1 : 2 molar ratio. Histidine-mediated Zn xylem loading seems to be a species-wide character in N. caerulescens. © 2014 New Phytologist Trust