Stem and leaf sequestration of zinc at the cellular level in the hyperaccumulator Sedum alfredii

Abstract

Summary• Sedum alfredii is a fast-growing, high-biomass zinc (Zn) hyperaccumulator native to China. Here, the characteristics of in vivo Zn distribution in stems and leaves of the hyperaccumulating (HE) and nonhyperaccumulating ecotypes (NHE) of S. alfredii were investigated by synchrotron radiation X-ray fluorescence (SRXRF) analysis, together with a Zn probe.• Preferential Zn accumulation in leaf and stem epidermis was observed in both ecotypes, but to a much greater extent for HE. Epidermal Zn increased largely in leaves and stems of HE as exposure time was prolonged, while Zn saturation occurred relatively early in HE leaf mesophyll cells and stem vascular bundles. A second peak of Zn enrichment in stem and leaf vascular systems was shown in both ecotypes. However, the proportion of Zn accumulated in stem vascular bundles relative to other tissues was much greater for HE than for NHE.• Leaf and stem distribution patterns of phosphorus (P) and sulphur (S) in the HE were very like that for Zn, while the calcium (Ca) distribution pattern was the reverse of that for Zn. No such relationship was observed in NHE.• Our study mainly suggested that epidermal layers serve as important storage sites for accumulated Zn in the S. alfredii HE.

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

“…In the present study the Zn concentration in the stem and leaf epidermis of S. plumbizincicola was > 5 times higher than that in the cortex and mesophyll, and Cd in the stem epidermis was also over 2.5 times higher than in the cortex. This is consistent with previous studies on Zn distribution in leaves of hydroponically cultured S. plumbizincicola Cao et al 2014) and is similar to other hyperaccumulators (Küpper et al 1999;Vogel-Mikuš et al 2008a;Tian et al 2009). These results indicate that the preferential sequestration of Zn in stem and leaf (and to a lesser extent of Cd in the stem) into the epidermis is an important mechanism for h y p e r a c c u m u l a t i o n a n d d e t o x i f i c a t i o n i n S. plumbizincicola.…”

“…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.…”

“…However, in the hyperaccumulator N. praecox Zn concentrations in the epidermis were approximately 5 times higher than that in the mesophyll, while Cd concentrations in the epidermis were only twice as high as or even similar to that in the mesophyll (Vogel-Mikuš et al 2008a, b). In the hyperaccumulator Sedum alfredii Zn accumulated preferentially in the epidermis and vascular bundles while Cd was localized mainly in parenchyma cells such as mesophyll in the leaves and cortex and pith in the stems (Tian et al 2009(Tian et al , 2011. On the other hand, most studies on cellular elemental localization use plant materials from artificial hydroponics systems with sufficient nutrients and elevated metal bioavailability.…”

“…Numerous studies suggest that heavy metal sequestration in less metabolically active parts of plants such as the epidermis and trichomes is one of the possible mechanisms for heavy metal detoxification in hyperaccumulators (Küpper et al 1999;Zhao et al 2000;Tian et al 2009;Hu et al 2009). 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).…”

The potential of wild vegetation species of Eleusine indica L., and Sonchus arvensis L. for phytoremediation of Cd-contaminated soil

“…Generally, hyperaccumulator plants adapt to heavy metal contaminated soil through the accumulation of heavy metals in the root system, the translocation of heavy metals from the root to the shoot, as well as through sequestration and detoxification of heavy metals in the leaves. Physiological and molecular characteristics determine the level of accumulation of heavy metals in plants (Tian et al, 2009;Oomen et al, 2009). Cd is a heavy metal that is most difficult to be absorbed.…”