Field evaluation of Cd and Zn phytoextraction potential by the hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri.

Field trials were undertaken to investigate the effect of the application of metal mobilizing agents, different sowing strategies and length of growing season on the extraction of Cd and Zn from soils by Thlaspi caerulescens and Arabidopsis halleri. None of the mobilizing agents used enhanced metal accumulation by T. caerulescens. Between 1998 and 2000, on average across plots where Cd or Zn exceeded allowable limits, T. caerulescens removed 1.3 and 0.3% of the total soil Cd and Zn. In one season when T. caerulescens was grown for 14 months, 21.7 and 4.4% of the total soil Cd and Zn was removed. This was larger than values found when T. caerulescens was grown for 4 months. A. halleri accumulated similar concentrations of Zn, but lower Cd concentrations than T. caerulescens. The results indicate that metal phytoextraction using T. caerulescens can be used to clean up soils moderately contaminated by Cd.

Arsenic hyperaccumulation by Pteris vittata from arsenic contaminated soils and the effect of liming and phosphate fertilisation.

Pot experiments were carried out to investigate the potential of phytoremediation with the arsenic hyperaccumulator Pteris vittata in a range of soils contaminated with As and other heavy metals, and the influence of phosphate and lime additions on As hyperaccumulation by P. vittata. The fern was grown in 5 soils collected from Cornwall (England) containing 67-4550 mg As kg(-1) and different levels of metals. All soils showed a similar distribution pattern of As in different fractions in a sequential extraction, with more than 60% of the total As being associated with the fraction thought to represent amorphous and poorly-crystalline hydrous oxides of Fe and Al. The concentration of As in the fronds ranged from 84 to 3600 mg kg(-1), with 0.9-3.1% of the total soil As being taken up by P. vittata. In one soil which contained 5500 mg Cu kg(-1) and 1242 mg Zn kg(-1), P. vittata suffered from phytotoxicity and accumulated little As (0.002% of total). In a separate experiment, neither phosphate addition (50mg P kg(-1) soil) nor liming (4.6 g CaCO3 kg(-1) soil) was found to affect the As concentration in the fronds of P. vittata, even though phosphate addition increased the As concentration in the soil pore water. Between 4 and 7% of the total soil As was taken up by P. vittata in 4 cuttings in this experiment. The results indicate that P. vittata can hyperaccumulate As from naturally contaminated soils, but may be suitable for phytoremediation only in the moderately contaminated soils.

Comparison of root absorption, translocation and tolerance of arsenic in the hyperaccumulator Pteris vittata and the nonhyperaccumulator Pteris tremula.

* Several fern species can hyperaccumulate arsenic, although the mechanisms are not fully understood. Here we investigate the roles of root absorption, translocation and tolerance in As hyperaccumulation by comparing the hyperaccumulator Pteris vittata and the nonhyperaccumulator Pteris tremula. * The two species were grown in a pot experiment with 0-500 mg As kg-1 added as arsenate, and in a short-term (8 h) uptake experiment with 5 microM arsenate under phosphorus-sufficient conditions. * In the pot experiment, P. vittata accumulated up to 2500 mg As kg-1 frond d. wt and suffered no phytotoxicity. P. tremula accumulated<100 mg As kg-1 frond d. wt and suffered severe phytotoxicity with additions of >or=25 mg As kg-1. In the short-term uptake experiment, P. vittata had a 2.2-fold higher rate of arsenate uptake than P. tremula, and distributed more As taken up to the fronds (76%) than did P. tremula (9%). * Our results show that enhanced root uptake, efficient root-to-shoot translocation, and a much elevated tolerance through internal detoxification all contribute to As hyperaccumulation in P. vittata.

Assessment of strain field in endothelial cells subjected to uniaxial deformation of their substrate.

A stretch chamber has been developed in order to visualize the deformation of cells subjected to controlled uniaxial stretch of their substrate. A rectangular, custom-made, transparent silicone channel is used as a deformable substrate. Bovine aortic endothelial cells are plated at the bottom of the channel whose lateral deformation is controlled by two piezoelectric translators. The system is mounted on the stage of a confocal microscope where three-dimensional (3D) images of the cells can be acquired simultaneously in the three RGB channels. The first channel provides images of 216 nm fluorescent beads embedded in the cytoskeleton (used as internal markers). The second is used to image the shape of the nucleus revealed by live cell nucleic acid staining. The third one provides a transmitted light image of the cell outline. 3D images of the cell are taken before deformation, after uniaxial deformation of the substrate (up to 25%) and after relaxation. Results indicate that: (a) the cell closely follows the deformation imposed by the substrate with no measurable residual strain after relaxation, and (b) there is a clear mechanical coupling between the extracellular matrix and the nucleus, which deforms significantly under the applied substrate stretch. Suggesting that the nucleus can directly sense the mechanical environment of the cell, the latter result has potentially important implications for signal transduction.