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

Abstract

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