Plant Science 127 (1997) 129–137 Response of antioxidant enzymes to excess copper in tomato (L ycopersicon esculentum , Mill.) Salma Mazhoudi a , Abdelilah Chaoui a , Mohamed Habib Ghorbal b , Ezzedine El Ferjani a, * a Bio -Physiologie Cellulaires, De ´partement des Sciences Naturelles, Faculte ´ des Sciences de Bizerte, 7021 -Z arzouna, T unisie b Nutrition et Me ´tabolisme Azote ´s, De ´partement des Sciences Biologiques, Faculte ´ des Sciences de Tunis, 1060 -Campus, T unis, T unisie Received 30 December 1996; received in revised form 2 May 1997; accepted 5 May 1997 Abstract 15-day-old seedlings of tomato (L ycopersicon esculentum, Mill., cv. Ibiza F 1 ) were treated, for 7 days, by addition of 50  M Cu to the nutrient medium. Under these conditions, a decrease in growth, more pronounced in leaves and in stems than in roots, was observed, as compared to controls. Copper accumulation was markedly higher in roots as compared to shoots. In all plant parts, excess copper induced an increase in the rate of lipid peroxidation. Catalase (CAT) activity was not modified in leaves and in stems, but it was decreased in roots. The activity of ascorbate peroxidase (APX) was unaltered in roots and in stems, while it was diminished in leaves. However, guaiacol peroxidase (GPX) activity was increased only in roots and stems. Enhancement of this activity was more important in stems than in roots. Analysis of the profile of anionic isoenzymes of GPX revealed quantitative and qualitative changes in roots and stems of stressed plants. These results, together, indicate that a toxic concentration of copper (50  M) induces oxidative stress and differential responses of antioxidant enzymes in plant parts. Activity level of GPX, but not APX nor CAT, increased in response to damage. © 1997 Elsevier Science Ireland Ltd. Keywords: Tomato; L ycopersicon esculentum ; Copper; Lipid peroxidation; Antioxidant enzymes; Oxidative stress A bbreiations: APX, Ascorbate peroxidase; CAT, Catalase; GPX, Guaiacol peroxidase; MDA, Malondialdehyde; PAGE, Polyacrylamide gel electrophoresis; PVP, Polyvinylpyrro- lidone; TBA-rm, 2-Thiobarbituric acid-reactive materials. *Corresponding author. Fax: +216 2 434566. 1. Introduction Copper is known to be an essential oligonutri- ent for plants, but it can also be a toxic element and its toxicity can be observed even at tissue 0168-9452/97/$17.00 © 1997 Elsevier Science Ireland Ltd. All rights reserved. PII S0168-9452(97)00116-7