Ability of transgenic poplars with elevated glutathione content to tolerate zinc(2+) stress Andra ´s Bittsa ´nszky a , Tama ´s Kfmives b, * , Ga ´bor Gullner b , Ga ´bor Gyulai a , Jo ´ zsef Kiss a , La ´szlo ´ Heszky a , La ´szlo ´ Radimszky c , Heinz Rennenberg d a Department of Genetics and Plant Breeding, HAS-SIU, Szent Istva ´n University, 2103 Go ¨do ¨llo ¨, Pa ´ter K. u. 1, Hungary b Plant Protection Institute, Hungarian Academy of Sciences, 1525 Budapest, P.O.B. 102, Hungary c Research Institute for Soil Science and Agricultural Chemistry, Hungarian Academy of Sciences, 1525 Budapest, P.O.B. 35, Hungary d Albert-Ludwigs-Universita ¨t, Institut fu ¨r Forstbotanik und Baumphysiologie, 79085 Freiburg i. Br., Georges-Ko ¨hler-Allee 53/54, Germany Available online 10 November 2004 Abstract Phytoremediation potentials of four poplar lines, Populus nigra (N-SL clone), Populus canescens , and two transgenic P. canescens clones were investigated using in vitro leaf discs cultures. The transgenic poplars overexpressed a bacterial gene encoding g-glutamylcysteine synthetase in the cytosol (11ggs) or in the chlopoplasts (6LgI), and therefore, they contained an elevated level of glutathione. Leaf discs of poplar clones were exposed to different concentrations of ZnSO 4 for 21 days. Zinc(2+) was phytotoxic only at high concentrations (10 À2 to 10 À1 M) at all P. canescens lines, but P. nigra was more sensitive. Transgenic poplars showed elevated heavy metal uptake as compared to the nontransformed clones. Treatments with zinc(2+) strongly induced the activity of glutathione S-transferase enzyme in untransformed poplar lines but to a lesser extent in the transgenic clones. These results suggest that transgenic poplars are more suitable for phytoremediation of soils contaminated with zinc(2+) than wild-type plants. D 2004 Elsevier Ltd. All rights reserved. Keywords: g-Glutamylcysteine synthetase; Glutathione; Heavy metal; Phytoremediation; Transgenic poplar; Zinc 1. Introduction Poplar plants have been shown to be excellent candidates for phytoremediation purposes. They can be cultivated at high rates of growth and produce a large biomass. Poplar trees have an extensive root systems ensuring efficient uptake of water containing the pollutants from the soil. Poplars allow several cycles of decontamination, their leaves can be easily collected and the contaminated biomass substantially reduced by incineration. The wood harvested may be used as valuable raw material for paper industry and the production of matches (Dietz and Schnoor, 2001; Ko ¨mives and Gullner, 2000; Ko ¨mives et al., 2003). Although poplars are known to take up several inorganic pollutants including heavy metals, such as cadmium (Koprivova et al., 2002), mercury (Rugh et al., 1998), and zinc (Di Baccio et al., 2003), their heavy metal tolerance is limited (Dietz and Schnoor, 2001). The remediative capacity of poplars can be significantly increased by genetic manipulations. Recently, poplar plants were transformed to overexpress the bacterial gene encoding g-glutamylcysteine synthetase (g-ECS, EC 3.2.3.3), which is the rate-limiting regulatory enzyme in the biosynthesis of the ubiquitous tripeptide thiol compound glutathione (GSH, g-l-glutamyl-l-cysteinyl-glycine; Noctor and Foyer, 1998). The transformed poplars contained higher levels of GSH and its precursor g-l-glutamyl-l-cysteine (g-EC) than the wild-type (Noctor et al., 1998). The increased production of GSH contributes to the antioxidative protection of plant cells against oxidative stress caused by various environ- mental factors (Noctor and Foyer, 1998). The glutathione 0160-4120/$ - see front matter D 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2004.10.001 Abbreviations: g-ECS, g-glutamylcysteine synthetase; GSH, gluta- thione; GST, glutathione S-transferase. * Corresponding author. Tel.: +36 1 48 77 521; fax: +36 1 48 77 555. E-mail address: tkom@nki.hu (T. Kfmives). Environment International 31 (2005) 251 – 254 www.elsevier.com/locate/envint