Enhanced Inducibility of Glutathione S-Transferase Activity by Paraquat in Poplar Leaf Discs in the Presence of Sucrose By G. GULLNER 1) , G. GYULAI 2) , A. BITTSÁNSZKY 2) , J. KISS 2) L. HESZKY 2) & T. KOMIVES 1) K e y w o r d s : Glutathione S-transferase, inducibility, oxidative stress, paraquat, poplar, sucrose Summary GULLNER G., GYULAI G., BITTSÁNSZKY A., KISS J., HESZKY L. & KOMIVES T. 2005. Enhanced inducibility of glutathione S-transferase activity by paraquat in poplar leaf discs in the presence of sucrose. - Phyton (Horn, Austria) 45 (3): (39)-(44). Leaf discs of the wildtype poplar hybrid Populus canescens and its two transgenic lines overexpressing γ-glutamylcysteine synthetase in the cytosol or in the chloroplasts were exposed to the herbicide paraquat (4 x 10 -9 to 4 x 10 -6 M). Leaf discs were incubated on tissue culture media containing 0.2, 1.0 or 2.0 % sucrose. Exposure to paraquat led to a concentration-dependent decrease of GST activities at 0.2 % sucrose. However, at higher external sucrose supplies, paraquat brought about marked inductions of GST activities in all poplar lines. The GST induction was light- dependent. Fluorescence measurements showed that the efficiency of the photosynthetic apparatus was inhibited by high paraquat concentrations (4 x 10 -7 - 4 x 10 -6 M) in all poplar clones. The photosynthetic efficiency (F v /F m ) decreased also in leaf discs incubated in continuous darkness in the presence of paraquat. Introduction A wide range of plant species are capable of removing and/or degrading toxic organic substances and heavy metals from polluted soils. Phytoremediation is an emerging new technology based on these phenomena (SALT & al. 1998, 1) Plant Protection Institute, Hungarian Academy of Sciences, 1022 Budapest, Herman Ottó u. 15, Hungary, e-mail: ggull@nki.hu 2) HAS-SIU Research Group, Department of Genetics and Plant Breeding, Szent István University, 2103 Gödöllő, Páter K. u. 1, Hungary. Phyton (Austria) Special issue: “D. Grill” Vol. 45 Fasc. 3 (39)-(44) 1.9.2005