Spatial distribution of cadmium in leaves of metal hyperaccumulating Thlaspi praecox using micro‐PIXE

Abstract

Summary• Localization of cadmium (Cd) and other elements was studied in the leaves of the field-collected cadmium/zinc (Cd/Zn) hyperaccumulator Thlaspi praecox from an area polluted with heavy metals near a lead mine and smelter in Slovenia, using micro-PIXE (proton-induced X-ray emission).• The samples were prepared using cryofixation. Quantitative elemental maps and average concentrations in whole-leaf cross-sections and selected tissues were obtained.• Cd was preferentially localized in the lower epidermis (820 µg g -1 DW), vascular bundles and upper epidermis, whereas about twice the lower concentrations were found in the mesophyll.• Taking into account the large volume of the mesophyll compared with the epidermis, the mesophyll is indicated as a relatively large pool of Cd, possibly involved in Cd detoxification/dilution at the tissue and cellular level.

Elemental distribution by cryo-micro-PIXE in the zinc and cadmium hyperaccumulator Sedum plumbizincicola grown naturally

“…In the leaf Ca was enriched mainly in the palisade mesophyll and to a lesser extent also in the spongy mesophyll and was depleted in the upper and lower epidermis, while K was enriched in the lower epidermis and spongy mesophyll. The same effect is common in most eudicots studied (Conn and Gilliham 2010) such as Citrus jambhiri (rough lemon) (Storey and Leigh 2004), N. praecox (Vogel-Mikuš et al 2008a) and Coriandrum sativum (coriander) (Kerton et al 2009). …”

“…Although measurements of Cd were possible on K and L x-ray lines, overlapping of Cd L group of lines with the K-alpha lines of K and Ca presents a potential danger of over-estimating Cd concentrations (Vogel-Mikuš et al 2008a) and only the results from Cd K group of lines, free of any interferences, are discussed further. Because the Cd maps of plant tissues are just at the detection limits, only Cd concentrations obtained from the selected regions of interest using the non-linear least squares fits are presented in Table 5.…”

“…A high Zn concentration in the xylem indicates efficient vertical transport via the xylem. Nevertheless, similar to many other species such as N. praecox (Vogel-Mikuš et al 2008a), Arabidopsis thaliana (Belleghem et al 2007) and S. alfredii (Tian et al 2009), considerable accumulation of Zn in the phloem of S. plumbizincicola suggests a strong translocation of this metal from shoots to other tissues. Moreover, in the stem of S. plumbizincicola the Zn concentration in the parenchyma surrounding the xylem indicates transverse transport of this element.…”

“…For example, in the hyperaccumulators Thlaspi caerulescens (now Noccaea caerulescens) and Noccaea praecox Zn and Cd were mainly concentrated in the epidermal cells of the leaf (Cosio et al 2005;Vogel-Mikuš et al 2008a) and in Arabidopsis halleri they were stored in the trichomes (Küpper et al 2000). Some studies have also indicated a dominant role of mesophyll cells in the compartmental detoxification of abundant heavy metals (Küpper et al 2000;Ma et al 2005;Tian et al 2011).…”

The changes of contents of selected free amino acids associated with cadmium stress in Noccaea caerulescens and Arabidopsis halleri

“…The changes of contents of selected free amino acids associated with cadmium stress in Noccaea caerulescens and Arabidopsis halleri V. Zemanová 1 , M. Pavlík 2 , D. Pavlíková 1 , P. Tlustoš 1 ment due to its larger volume (Vogel-Mikuš et al 2008). In leaf cells of hyperaccumulators, metals are generally sequestered in vacuoles (Huguet et al 2012).…”