Isabelle Laffont-Schwob

Characterization of Metal Tolerance and Accumulation in Grevillea Exul VAR Exul

Grevillea exul var exul (Proteaceae), a tree species native to serpentine soils in New Caledonia, is a reported manganese accumulator. Since the metal tolerance of this species remains unknown, its growth and metal accumulation were studied for seven heavy metals under controlled conditions. Brassica juncea, a popular species for metal phytoremediation, was used as a reference. G. exul seedlings were more tolerant to Cr, Zn, Ni, and Cu than B. juncea. There were no differences in Hg, and Cd tolerance between both species. B. juncea seedlings concentrated more Cd, Hg, and Cr in their shoot than G. exul seedlings, while Ni, Zn, and Mn levels were similar for both species. Comparison then focused on tolerance at toxic doses of Ni and Mn using older individuals of both species. No growth inhibition for G. exul plants was observed, whereas the growth of B. juncea was significantly inhibited at the higher metal concentrations. Shoot Mn and Ni concentrations were again lower in G. exul plants as compared to B. juncea, suggesting a mechanism of partial Ni and Mn exclusion in G. exul. In a subsequent study, 1-year-old G. exul plants favored Ni accumulation in roots while Mn accumulated preferentially in shoots.

Anatomical element localization by EDXS in Grevillea exul var. exul under nickel stress

Grevillea exul var. exul, an endemic serpentinic Proteaceae of New Caledonia, was chosen to study the spatial distribution of Ni because this species supports strong content of metals, which can allow important absorptions thus detectable by microanalysis. Fine transversal sections of axenic G. exul var. exul plants grown during 15 days on nickel sulphate medium were examined by EDXS microanalysis. It showed that in Ni treated plants, Ni was concentrated mostly in the phloem compared to the xylem and the epidermis, either in roots or in the basal part of the stems and was mostly in the epidermis in the upper part of the stems and not detectable in the leaves. This metal took the place of P and K in the treated plants whereas the localization of these macroelements was quite uniform in control sections. We assume that a mechanism of phloem loading is implicated to restrict Ni accumulation in G. exul var. exul.

Heavy Metal and Arsenic Resistance of the Halophyte Atriplex halimus L. Along a Gradient of Contamination in a French Mediterranean Spray Zone

Elements uptake, histological distributions as well as mycorrhizal and physiological statuses of Atriplex halimus were determined on trace metal and metalloid polluted soils from the surrounding spray zones of a former lead smelter in the South-East coast of Marseille (France). Analyses of heavy metal and arsenic distribution in soil and plant organs showed that A. halimus tolerance is largely due to exclusion mechanisms. No specific heavy metal concentration in leaf or root tissues was observed. However, accumulation of salts (NaCl, KCl, Mg and Ca salts) on leaf bladders and peripheral tissues of roots was observed and may compete with metal element absorption. Occurrence of endomycorrhizal structures was detected in roots and may contribute to lower element transfer from root into the aerial parts of plants. The non-destructive measurements of leaf epidermal chlorophylls, flavonols and phenols showed a healthy state of the A. halimus population on the metal and metalloid polluted sites. Considering the low metal bioaccumulation and translocation factors along with a reduced metal stress diagnosis, A. halimus appeared as a good candidate for phytostabilization of trace metals and metalloids and notably arsenic in contaminated soils of the Mediterranean spray zone. However, its invasive potential has to be determined before an intensive in situ use.