Heavy metal accumulation in Halimione portulacoides: Intra- and extra-cellular metal binding sites

Abstract

Salt marsh plants can sequestrate and inherently tolerate high metal concentrations found in salt marsh sediments. This work intended to understand the Halimione portulacoides (L.) Aellen strategies to prevent metal toxicity, by investigating the metal location in different plant organs and in the cell. A sequential extraction was performed on leaves, stems and roots of H. portulacoides in order to determine and compare the metal (Zn, Pb, Co, Cd, Ni and Cu) concentration in several fractions of the plant material (ethanolic, aqueous, proteic, pectic, polissacaridic, lenhinic and cellulosic). This study shows that all plant organs of H. portulacoides mostly retain metals in the cell wall (65% is the average for all studied metals stored in the root cell wall, 55% in the stems and 53% in the leaves), and the metal content in the intracellular compartment is much lower (21% in roots, 25% in stems and 32% in leaves). High levels of heavy metal in the sedimentary environment do not cause toxicity to H. portulacoides, because H. portulacoides immobilizes them in different cell compartments (cell wall+proteic fraction+intracellular) outside key metabolic sites.

Heavy metal content in halophytic plants from inland and maritime saline areas

“…This was also shown by the low translocation factor in all the investigated plant species. Sousa et al [7] reported that the translocation factor in Halimione portulacoides was lower than 1, which this study confirms. The high mobility of Ni and Zn [7,15] may explain the highest translocation factors observed for these metals when considering the allocation of metals from the root to the leaves and from the root to the stems.…”

“…The same kind of distribution was reported for Zn, Cu, Ni and Co in Halimione portulacoides from the Tagus estuary by Sousa et al [7]. Populations of Suaeda maritima from the inland saline areas preferred accumulation of metals in the above-ground parts (stems and leaves), while populations of the same species from the maritime saline areas preferred accumulation in the root.…”

“…The translocation factor (TNF) was calculated by the ratio of [metal] leaves /[metal] roots (TNF3) and also by the ratio of [metal] stem /[metal] roots (TNF2), expressing the metal's translocation within the plant, from the root to the leaves and the stem [7]. The TNF from the soil to the roots was also calculated (TNF1).…”

Mercury intracellular partitioning and chelation in a salt marsh plant, Halimione portulacoides (L.) Aellen: Strategies underlying tolerance in environmental exposure

“…Our results show that more than 93% of the total mer cury found in the roots was immo bi lized in the cell walls and 72% of the total mer cury found in the leaves were in the also in the cell walls. Sousa et al (2008) found that in the pres ence of other met als (Zn, Pb, Co, Cd, Ni and Cu) simi lar results were obtained, with met als being mostly retained in the cell wall com part ments. Accord ing to Zor noza et al (2002), a higher accu mu la tion of met als in cell walls can func tion as a pro tec tion bar rier by reduc ing the metal con cen tra tion in the cyto plasm.…”

Utilización de Sustancias Húmicas Comerciales para Optimizar la Fitorremediación de Suelos Mineros Usando Vetiveria (Chrysopogon zizanioides L. Roberty) y Verdolaga (Atriplex portulacoides L.)

“…Moreno et al, 2013;Cambrollé et al, 2012a;Cambrollé et al, 2012b;Sousa et al, 2008). Esta gran tolerancia se debe a los eficientes mecanismos de detoxificación y compartimentalización que presenta esta especie; los metales están principalmente asociados a la pared celular de las células vegetales, lo que actúa de barrera contra los efectos nocivos de los metales al mantenerlos alejados del citoplasma y otros orgánulos intracelulares con actividad metabólica (Sousa et al, 2008).…”