Research article Changes of antioxidants levels in two maize lines following atrazine treatments M.M. Nemat Alla * , N.M. Hassan Botany Department, Faculty of Science at Damietta, Mansoura University, Damietta, Egypt Received 9 August 2005 Available online 05 June 2006 Abstract Growth and antioxidants levels of shoot of 10-d-old maize lines (Zea mays L. Hybrid 351 and Giza 2) differentially responded to atrazine treatment at the recommended field dose (RFD) during the following 20 d. Atrazine significantly reduced shoot fresh and dry weights but significantly accumulated H 2 O 2 , lipid peroxides and carbonyl groups in Giza 2 during the whole experiment; an effect that prolonged with either elapse of time or increasing the herbicide dose. Meanwhile, ascorbic acid (AsA) and reduced glutathione (GSH) contents were significantly decreased along with significant inhibitions in activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.7), guaiacol peroxidase (GPX; EC 1.11.1.7), and glutathione-S-transferase (GST; EC 2.5.1.18). Similar responses were observed in Hybrid 351 only during the first 12 d, and seemed to be overcome thereafter. These findings indicate an induced oxidative stress in maize following atrazine treatments. Such state appeared to be counterbalanced in Hybrid 351 but continued in Giza 2 concluding Giza 2 as more susceptible to atrazine than Hybrid 351. Therefore, the differential susceptibility of Giza 2 to atrazine is related to deficiency in antioxidant levels. © 2006 Elsevier SAS. All rights reserved. Keywords: Antioxidants; Atrazine; Maize; Oxidative stress; Peroxidase–catalase activity; Tolerance 1. Introduction Atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5- triazine], is a photosynthetic herbicide blocks the flow of elec- trons through PSII, and thus blocks the transfer of excitation energy from chlorophyll molecules to the PSI reaction center. Excited chlorophyll molecules (singlet chlorophyll) sponta- neously form triplet chlorophyll which reacts with O 2 to form singlet oxygen ( 1 O 2 ) inducing the formation of reactive oxygen species (ROS). They typically result from the excitation of O 2 to form 1 O 2 or from the transfer of one, two or three electrons to O 2 to form, respectively, a superoxide radical (O 2 – ), hydro- gen peroxide (H 2 O 2 ) or a hydroxyl radical (HO – ) [22]. The key step in oxidative stress is the production of ROS which initiate a variety of autooxidative chain reactions on membrane unsa- turated fatty acids, producing lipid hydroperoxides and thereby cascade of reactions ultimately leading to destruction of orga- nelles and macromolecules [7]. Antioxidants are crucial for plant defense against oxidative stress. Removal of ROS are regulated by antioxidant enzymes such as superoxide dismu- tase (SOD), catalase (CAT) and peroxidases and various other endogenous antioxidants such as ascorbate (AsA), glu- tathione (GSH) and the associated glutathione metabolism enzyme [4,7,14,22,25,26]. Some herbicides produce oxidative stress [33]. Plant tolerance to herbicides might confer by differ- ential antioxidative mechanism. In addition, glutathione-S- transferases (GSTs) which are mostly involved in the detoxica- tive conjugation of some xenobiotics having an electrophilic group with GSH can also act as peroxidases. Therefore, this work was aimed to relate the differential tolerance of two www.elsevier.com/locate/plaphy Plant Physiology and Biochemistry 44 (2006) 202–210 Abbreviations: APX, ascorbate peroxidase; AsA, ascorbic acid; CAT, catalase; CDNB, 1-chloro-2,4-dinitrobenzene; DTT, dithiothreitol; GPX, guaiacol peroxidase; GSH, reduced glutathione; GST, glutathione-S- transferase; MDA, malonaldehyde; NBT, nitroblue tetrazolium; PMSF, phenylmethylsulfonyl fluoride; RFD, recommended field dose; ROS, reactive oxygen species; SOD, superoxide dismutase; TBA, thiobarbituric acid; TCA, trichloroacetic acid. * Corresponding author. Tel./fax: +20 57 40 3868. E-mail address: mamnematalla@mum.mans.edu.eg (M.M. Nemat Alla). 0981-9428/$ - see front matter © 2006 Elsevier SAS. All rights reserved. doi:10.1016/j.plaphy.2006.05.004