Poster: Heavy metals & phytoremediation

Abs # 42: Characterization and expression of Metallothioneins in the aquatic fern Azolla filiculoides under heavy metals stress

Presenter:	Schor-Fumbarov, Tamar , schor@agri.huji.ac.il
Authors	Schor-Fumbarov, Tamar  (A)   Tel-Or, Elisha  (A)
Affiliations:	(A): The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, The Institute of Plant Sciences

Our laboratory is involved in the characterization and application of active uptake and passive absorption of metals by the aquatic fern Azolla filiculoides. Cadmium, copper, nickel, zinc, chromium, iron and uranium were accumulated and stored in Azolla plants, grown in the presence of 10mg/l metal, reaching 5-6 mg metal/gr Azolla dry weight. In the present study we suggest that Azolla Metallothioneins (MTs) are involved in the accumulation of metals in the plant cell. MTs are cysteine-rich peptide, with the unique ability to form stable metal-thiolate clusters (heavy metal-binding protein molecules) and they are gene-encoded polypeptides. Azolla is hosting the symbiotic cyanobacterium Anabaena azollae. We have introduced the antibiotics erythromycin to eliminate Anabaena, and were able to confirm that Azolla MT is specific for the host Azolla and does not originate from the symbiotic Anabaena. We isolated type 2 MT- AzMT2 (accession no. AF482470) from Azolla filiculoides, and the sequence contains two cysteine-rich domains separated by spacer of 27 amino acid residues. The identity and homology of the Azolla MT2 to other plants metallothioneins (Brassica oleracea, Avicennia marina) is 42% and 54% respectively. Semiquantitative RT-PCR showed that AzMT2 transcripts increase in response to different concentrations of heavy metals, such as Cd, Cu, Ni and Zn. Our results showed that AzMT2 protein has been expressed in E.coli in the presence of 200μM Cd. To confirm the identity of the expressed peptide, we used electrospray ionization-mass spectrometry analysis. Acknowledgement: We thank Prof. Peter Goldsbrough, Purdue University, USA, for his interest, hospitality and contribution and Prof. Zach Adam for his suggestions.