Differential metal‐specific tolerance and accumulation patterns among Thlaspi caerulescens populations originating from different soil types

Abstract

Summary• Here, Thlaspi caerulescens populations from contrasting soil types (serpentine, calamine and nonmetalliferous) were characterized with regard to tolerance, uptake and translocation of zinc (Zn), cadmium (Cd) and nickel (Ni) in hydroponic culture.• Results showed that high-level tolerances were apparently metal-specific and confined to the metals that were enriched at toxic levels in the soil at the population site.• With regard to metal accumulation, results suggested that, unlike Zn hyperaccumulation, Cd and Ni hyperaccumulation were not constitutive at the species level in T. caerulescens .• In general, the populations under study exhibited a pronounced uncorrelated and metal-specific variation in uptake, root to shoot translocation, and tolerance of Zn, Cd and Ni. The distinct intraspecific variation of these characters provides excellent opportunities for further genetic and physiological dissection of the hyperaccumulation trait.

Isolation of Zn-responsive genes from two accessions of the hyperaccumulator plant Thlaspi caerulescens

“…Two diVerent Zn exposures and two Thlaspi accessions known to diVer in their Zn tolerance, rootto-shoot transport and accumulation were chosen for this experiment. The LE accession accumulates approximately fourfold Zn and has a higher root-toshoot accumulation ratio for Zn compared to LC accession (Assunção et al 2003a). On the other hand, LC has much higher tolerance to Zn than does LE.…”

“…Based on Southern analysis, the diVerences in the expression between the two accessions are not due to diVerences in gene copy number (data not shown). The St Félix-de-Pallières and LC accessions are equally tolerant to Zn (Assunção et al 2003a), implying that higher levels of MT2 correlate with Zn tolerance. Zn treatment increases the expression of MT2 in the shoots of LC, and also of St Félix-de-Pallières (Roosens et al 2005) as well as in Arabidopsis seedlings (Zhou and Goldsbrough 1994).…”

“…The MT2 expression at low Zn concentrations (0.2 M) in the shoots was equally high in the sensitive LE and in the tolerant LC accessions. Since metal accumulation in LE shoots is high already at low external Zn (Assunção et al 2003a), it is possible that the higher expression reXects an increased requirement/ability for metal binding.…”

“…The expression of TcMT3 was up-regulated by Zn in the Thlaspi shoots, higher levels being present in LE than in LC, particularly at higher Zn exposures. Since LE is known to accumulate higher concentrations of Zn in the shoots (Assunção et al 2003a), the TcMT3 levels appear to reXect the shoot Zn levels and may thus have a function in metal homeostasis under Zn exposure.…”

“…The growth conditions were as described by Assunção et al (2003a). Seedlings grown for 3 weeks in moist peat were transferred to hydroponic solution and, after 1 week of cultivation, were exposed to 0, 2, 10 or 100 M ZnSO 4 , LC also to 1,000 M ZnSO 4 for additional 2 weeks.…”