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JXB Advance Access originally published online on May 7, 2008
Journal of Experimental Botany 2008 59(8):2205-2219; doi:10.1093/jxb/ern092
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Overexpression of phytochelatin synthase in tobacco: distinctive effects of AtPCS1 and CePCS genes on plant response to cadmium

Sylwia Wojas1, Stephan Clemens2, Jacek Hennig3, Aleksandra Sklodowska1, Edyta Kopera3, Henk Schat4, Wojciech Bal3 and Danuta Maria Antosiewicz1,*

1University of Warsaw, Faculty of Biology, Miecznikowa str.1, 02–096 Warszawa, Poland
2University of Bayreuth; Department of Plant Physiology, Universitaetsstrasse 30; D-95440 Bayreuth, Germany
3Institute of Biochemistry and Biophysics PAS, Pawinskiego str. 5A, 02-106 Warszawa, Poland
4Free University of Amsterdam, Faculty of Earth and Life Sciences, De Boelelaan 1087, 1081 HV Amsterdam, Netherlands

* To whom correspondence should be addressed. E-mail: dma{at}biol.uw.edu

Phytochelatins, heavy-metal-binding polypeptides, are synthesized by phytochelatin synthase (PCS) (EC 2.3.2.15 [EC] ). Previous studies on plants overexpressing PCS genes yielded contrasting phenotypes, ranging from enhanced cadmium tolerance and accumulation to cadmium hypersensitivity. This paper compares the effects of overexpression of AtPCS1 and CePCS in tobacco (Nicotiana tabacum var. Xanthi), and demonstrates how the introduction of single homologous genes affects to a different extent cellular metabolic pathways leading to the opposite of the desired effect. In contrast to WT and CePCS transformants, plants overexpressing AtPCS1 were Cd-hypersensitive although there was no substantial difference in cadmium accumulation between studied lines. Plants exposed to cadmium (5 and 25 µM CdCl2) differed, however, in the concentration of non-protein thiols (NPT). In addition, PCS activity in AtPCS1 transformants was around 5-fold higher than in CePCS and WT plants. AtPCS1 expressing plants displayed a dramatic accumulation of {gamma}-glutamylcysteine and concomitant strong depletion of glutathione. By contrast, in CePCS transformants, a smaller reduction of the level of glutathione was noticed, and a less pronounced change in {gamma}-glutamylcysteine concentration. There was only a moderate and temporary increase in phytochelatin levels due to AtPCS1 and CePCS expression. Marked changes in NPT composition due to AtPCS1 expression led to moderately decreased Cd-detoxification capacity reflected by lower SH:Cd ratios, and to higher oxidative stress (assessed by DAB staining), which possibly explains the increase in Cd-sensitivity. The results indicate that contrasting responses to cadmium of plants overexpressing PCS genes might result from species-dependent differences in the activity of phytochelatin synthase produced by the transgenes.

Key words: Cadmium, {gamma}-glutamylcysteine, glutathione, phytochelatins, tobacco

Received 22 December 2007; Revised 2 March 2008 Accepted 3 March 2008


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