Poster: Heavy Metals

Abs # 111: The role of CNGC in Ni²⁺ influx into tobacco root cell protoplasts

Presenter:	Atzmon-Novik, Nirit , nirit_a@yahoo.com
Authors	Atzmon-Novik, Nirit  (A)   Moran, Nava  (A)   Kaplan, Boaz  (B)   Fromm, Hillel  (C) (D)  Fumbar-Dahan, Mirit  (A)
Affiliations:	(A): Inst. Plant Sci. Gen. Agric., The Hebrew University of Jerusalem, Rehovot 76100, Israel nava.moran@huji.ac.il (B): Dept. Plant Sciences, Weizmann Inst. Sci., Rehovot, 76100 Israel (C): School of Biology, University of Leeds, Leeds, UK (D): Dept. Plant Sciences Tel Aviv University, Tel Aviv, Israel
Web Site:	http://departments.agri.huji.ac.il/botany/moran.html

Nickel is vital to life in small amounts but toxic at higher concentrations both to plants and to animals. Like other heavy metals accumulated by plants, it is passed further on to animals and humans in a food-chain, along with the accompanying hazards. Yet, in spite of this importance of heavy metal uptake by plants, very little is known about the uptake mechanisms. A transgenic line of tobacco (Nicotiana tabacum) plants, overexpressing NtCBP4, a calmodulin-(CaM)-binding and a cyclic-nucleotide-gated channel (CNGC; Leng et al., 2002, Plant Physiol. 128:400), were more tolerant to Ni²⁺ compared to the wild type. This tolerance was associated with reduced plant Ni²⁺ accumulation (Arazi et al, 1999. Plant J. 20:171). In an attempt to elucidate the mechanisms of reduced plant Ni²⁺ levels and improved resistance, we sought to characterize the pathway of Ni²⁺ influx into root cells. To this end, we investigated the initial Ni²⁺ influx rate into isolated tobacco root protoplasts, monitoring it with the Ni²⁺-sensitive fluorescent dye, Newport Green. The rate of elevation in fluorescence emission following a bath exposure to 1mM NiSO₄ was significantly lower in root protoplasts from seedlings of transgenic plants overexpressing the NtCBP4 compared to the wild type. This suggests that the overexpression of NtCBP4 impairs Ni²⁺ influx to the root cells, consistent with previous findings. Protoplasts of a different transgenic line, expressing a truncated version of the NtCBP4 (C-terminus removed; Sunkar et al., 2000; Plant Journal 24:533) had significantly higher rate of influx, and did not differ from the wild type. Thus, the C terminus of the NtCBP4 may be important to the regulation of Ni²⁺ influx. Supported by a Korea-Israel grant #1132 from Israel Ministry of Science to NM