Investigation of three Mediterranean plant species suspected to accumulate and tolerate high cadmium and zinc levels : morphological, physiological and biochemical characterization under controlled conditions
(2007)
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- The aim of our study was to analyse the relationship between growth and Cd or Zn accumulation in three Mediterranean plant species present on a heavy metal contaminated site (mining area of La Unión; Carthagena; SE Spain). Seeds from Zygophyllum fabago L., Atriplex halimus L. and Dorycnium pentaphyllum Scop were collected on mature plants growing on heavy metal-contaminated soils and the obtained seedlings were maintained in nutrient solution in the presence of various doses of Cd or Zn under controlled environmental conditions. In order to investigate cellular components of metal toxicity, callus cultures were also performed. A growth increase was observed in response to low levels of Cd (1 µM) or Zn (10 µM), while higher metal levels have a deleterious impact on plant growth and morphology in the three considered plant species. Both metals reduced the internode length of the main stem and growth of ramifications. Negative effects of Cd were higher in young than in old tissues. The considered plant species displayed various strategies to cope with heavy metals. Dorycnium pentaphyllum and Zygophyllum fabago were able to regulate heavy metal absorption and translocation from the roots to the shoots while Atriplex halimus excreted heavy metals at the leaf surface through trichomes. Heavy metal stress induced a secondary water stress and an oxidative constraint. Water deficit was quantified in relation to a decrease in water and osmotic potential, stomatal conductance and water content. Physiological properties allowing drought resistance in the tested plant species may contribute to their ability to tolerate high concentrations of heavy metals. However, the highest ability of water stress-resistant cell line to cope with Cd stress was not related to any strategy of Cd exclusion but to the restriction of oxidative stress in relation to the oversynthesis of endogenous antioxidants. A limited diffusion of CO2 indicated by a decrease in carbon isotope discrimination as well as a decrease in the efficiency of photosystem II lead to a decrease in photosynthesis in response to Cd but not in response to Zn. Synthesis of glycinebetaine, proline, polyamines and sugars may play a key tool in both osmotic adjustment and protection of cellular structure. The C4 xero-halophyte Atriplex halimus also produced high amounts of oxalic acid, especially in the stems, as a strategy of tolerance. This species also specifically accumulated Na in response to Cd stress but chloride salinity reduced Cd accumulation and decreased the proportion of excreted Cd. The three tested species exhibited higher levels of heavy metals in the roots than in the shoots. However, between 130 and 250 mg Cd .kg DW-1 and between 530 and 830 mg Zn .kg DW-1 were found in the shoot parts, depending on the considered species, tested population, external doses and plant ontogenic stages. These species should then be tested in the future in field conditions for their ability to extract Cd and Zn from contaminated areas.
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Lefèvre, I. (2007). Investigation of three Mediterranean plant species suspected to accumulate and tolerate high cadmium and zinc levels : morphological, physiological and biochemical characterization under controlled conditions. https://hdl.handle.net/2078.5/124112