Response of Antioxidant Enzymes, Ascorbate and Glutathione Metabolism towards Cadmium in Hyperaccumulator and Nonhyperaccumulator Ecotypes of Sedum alfredii H. Xiaofen Jin, 1 Xiaoe Yang, 1 Qaisar Mahmood, 1 Ejazul Islam, 1,2 Dan Liu, 1,3 Hong Li 1 1 Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Natural Resources Science, Zhejiang University, Hangzhou 310029, People’s Republic of China 2 Nuclear Institute of Agriculture, Tandojam, Hyderabad 48800, Pakistan 3 School of Tourism and Health, Zhejiang Forestry College, Lin’an 311300, People’s Republic of China Received 18 September 2007; revised 11 November 2007; accepted 16 November 2007 ABSTRACT: Hydroponics studies were conducted to investigate the antioxidant adaptations, ascorbate and glutathione metabolism in hyperaccumulating ecotype of Sedum alfredii (HE) exposed to high Cd envi- ronment, when compared with its nonhyperaccumulating ecotype (NHE). Exposure to Cd induced a burst of oxidative stress in both ecotypes which was evident by the sharp increase in hydrogen peroxide (H 2 O 2 ) con- tents and lipid peroxidation. Buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, did not affect H 2 O 2 concentrations as well as growth of both ecotypes in the absence of Cd. However, compared with Cd application alone, BSO combined with Cd treatment caused a substantial augmentation of H 2 O 2 accumulation accompanied by a reduction in Cd concentrations in roots and leaves of HE at the end of treat- ment, which may rule out the possibility that GSH biosynthesis may play an important role as a signal of the stress regulation. No efficient and superior enzymatic antioxidant defense mechanisms against Cd-imposed oxidative stress existed in both NHE and HE, but the essential nonenzymatic components like ascorbic acid (AsA) and GSH played a prominent role in tolerance against Cd. Cadmium stimulated a notable rise in AsA concentration in both ecotypes soon after the application of treatment. A preferential Cd-stress response in HE was suggested to changes in the GSH pool, where acclimation was marked by increased GSH concen- trations. # 2008 Wiley Periodicals, Inc. Environ Toxicol 23: 517–529, 2008. Keywords: antioxidant; buthionine sulfoximine; glutathione; heavy metal; hyperaccumulation; Sedum alfredii Hance INTRODUCTION Increased cadmium emission is extremely dangerous because of its high mobility in the food chains. Plant species differ markedly in uptake and tolerance to Cd and other heavy met- als. Metal-hyperaccumulating plants typically store large amounts of metals in their aerial parts (Baker and Walker, 1990), which renders hyperaccumulators highly suitable for phytoremediation. To exploit full potential of Correspondence to: X. Yang; e-mail: xyang581@yahoo.com Contract grant sponsor: National Natural Science Foundation of China. Contract grant number: 30630046. Contract grant sponsor: Science and Technology Ministry of China. Contract grant number: 2002CB410804. Contract grant sponsor: Program for Changjiang scholars and Innova- tive Research Team. Contract grant number: IRT0536. Published online 23 January 2008 in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/tox.20362  C 2008 Wiley Periodicals, Inc. 517