Phytoextraction with Brassica napus L.: A tool for sustainable management of heavy metal contaminated soils.

Phytoextraction is a promising tool to extract metals from contaminated soils and Brassica napus L. seems to be a possible candidate species for this purpose. To select accessions with the ability to accumulate cadmium, hydroponically grown 21 day old seedlings of 77 B. napus L. accessions were exposed to 0.2 μM CdS

Combined expression of the Arabidopsis metallothionein MT2b and the heavy metal transporting ATPase HMA4 enhances cadmium tolerance and the root to shoot translocation of cadmium and zinc in tobacco

We expressed the AtMt2b and AtHMA4 genes under the 35S cauliflower mosaic virus promoter simultaneously in Nicotiana tabacum (SR1), using leaf disc transformation. A single AtMT2b tobacco T2 line was used for re-transformation with AtHMA4 to obtain the double transformant. Cadmium (Cd) and zinc (Zn) tolerance, uptake and translocation were measured in the double transformant, and compared to untransformed ('wild type') tobacco and single gene transformants. The double transformant exhibited enhanced Cd-tolerance, enhanced Cd and Zn root to shoot transport, but unaltered Zn tolerance and Cd and Zn uptake, compared with wild type.The single transformant lines did not show significant phenotypes. Our results suggest that the phenotypes of the double transformant are due to synergistic interaction between the transgenes. Except for Cd tolerance, the phenotypes were moderate for Cd and Zn root to shoot transport, which may be due to use of the 35S promotor, resulting in incorrect tissue-specificity. © 2010 Elsevier B.V

Dualities in plant tolerance to pollutants and their uptake and translocation to the upper plant parts.

There is a duality in plant tolerance to pollutants and ist response to the pollutants' stress. On the one hand some plants, (hyper)tolerant to heavy metals, are able to hyperaccumulate these metals in shoots, which could be beneficial for phytoremediation purposes to clean-up soil and water. On the other hand tolerant food crops, exposed to heavy metals in their growth medium, may be dangerous as carriers of toxic metals in the food chain leading to food toxicity. There is an additional duality in plant tolerance to heavy metals and that is in food crops that are tolerant and/or hyperaccumulators, which could be used on one hand for phytoremediation, under controlled conditions and on the other hand for food fortification with essential metals. Similarly, plants are also exposed to a large number of xenobiotic organic pollutants. Because they generally cannot avoid these compounds, plants take up, translocate, metabolize and detoxify many of them. There is a large variability in tolerance (defence) mechanisms against organic pollutants among plant species. This includes production of reductants but also scavenger molecules like ascorbate and glutathione and expression of the P-450 defence system, and superfamilies of the enzymes glutathione- and glucosyl-transferases. Again, with view to organic pollutants, plant detoxification mechanisms might well protect the plant itself, but produce compounds with some deleterious potential for other organisms. In this review we discuss these dualities on the basis of examples of agricultural and 'wild' species exposed to metal contaminants (mainly Cd) and organic pollutants. Differences in uptake and translocation of various pollutants and their consequences will be considered. We will separately outline the effects of the organic and non-organic Pollutants on the internal metabolism and the detoxification mechanisms and try to indicate the differences between both types of pollutants. Finally the consequences and solutions of these dualities in plant tolerance to pollutants will be discussed

High-level Zn and Cd tolerance in Silene paradoxa L. from a moderately Cd- and Zn-contaminated copper mine tailing.

Cadmium and zinc tolerance were examined in populations of Silene paradoxa, one from uncontaminated calcareous soil (CVD) and one from a mine tailing (FC) (Cd < 1-15 ppm, Zn 400-1300 ppm, pH 2-6). The mine population exhibited extremely high Zn and Cd tolerance levels, although the degrees of Cd and Zn enrichment relatively low at the population site. Cd and Zn hypertolerance in FC were associated with reduced rates of accumulation of these metals, both in roots and shoots (Cd), or exclusively in shoots (Zn). However, exclusion potentially explained only a minor part of the superior tolerance in FC. Cd hypertolerance in FC was associated with decreased, rather than enhanced phytochelatin accumulation. The remarkably high levels of Cd and Zn hypertolerance in FC might relate to the low soil pH, due to oxidation of sulphide minerals, and the absence of soil organic matter at the FC site. © 2008 Elsevier Ltd. All rights reserved

Real-time PCR analysis of metallothionein-2b expression in metallicolous and non-metallicolous populations of Silene vulgaris (Moench) Garcke.

In this paper we aimed to assess the role of metallothionein-2b in Zn or Cd hypertolerance by analyzing the expression of SvMT2b in roots of metallicolous and non-metallicolous Silene vulgaris populations, as well as in interpopulation crosses segregating for tolerance to Zn or Cd. Plants were grown in hydroponic nutrient solution and Zn and Cd were supplied as sulphates after 1 week of preculture. After 14 d of growth, RNA samples were taken from roots of plants exposed to different concentrations of Zn or Cd (2, 20, 200 μM Zn; 0, 2.5, 12.5 μM Cd) for 72 h. SvMT2b transcript levels were analyzed by real-time qPCR and compared to an Actin II control. Populations from cupriferous and calamine soil had significantly higher expression than non-metallicolous populations (P < 0.001). Although there was variation between the means of SvMT2b transcript levels among selection lines (P < 0.001), there was no overall significant difference between the Zn-hypertolerant and non-Zn-hypertolerant lines (P > 0.10) Metals did not significantly affect SvMT2b expression in any of the populations (P > 0.10). No co-segregation of Zn and Cd tolerance was observed, nor was any co-segregation of SvMT2b expression and Zn or Cd tolerance seen. It is concluded that Zn and Cd tolerance are genetically independent traits. Further we conclude that enhanced SvMT2b expression is not a primary determinant of naturally selected Zn or Cd hypertolerance. The enhanced expression in populations from calamine soils without Cu enrichment could be related to Cu homeostasis or, alternatively, point to a role as a non-metal specific hypostatic enhancer in metal hypertolerance. The possible role for SvMT2b in heavy metal tolerance is discussed. © 2005 Elsevier B.V. All rights reserved