Journal of Food, Agriculture & Environment, Vol.6 (3&4), July-October 2008 439 Influence of excess copper on lettuce (Lactuca sativa L.) grown in soil and nutrient solution Tihana Tekli 1 , Meri Engler 1 , Vera Cesar 2 , Hrvoje Lepeduš 2 , Nada Para ikovi 3 *, Zdenko Lon ari 1 , Ivna Štolfa 2 , Tatjana Marotti 4 , Nevenka Mikac 5 and Neven arkovi 6 1 Department of Agroecology, Faculty of Agriculture, University of J. J. Strossmayer, Trg Sv. Trojstva 3, HR-31000 Osijek, Croatia. 2 Department of Biology, University of J. J. Strossmayer, Trg Lj. Gaja 6, HR-31000 Osijek, Croatia. 3 Department of Plant Production, Faculty of Agriculture, University of J. J. Strossmayer, Trg Sv. Trojstva 3, HR-31000 Osijek, Croatia. 4 Laboratory for Biological Response Modifiers, Division of Molecular Medicine, Rudjer Boskovic Institute, Bijeni ka 54, HR- 10000 Zagreb, Croatia. 5 Laboratory for Physical Chemistry of Traces, Division for Marine and Environmental Research, Rudjer Boskovic Institute, Bijeni ka 54, HR-10000 Zagreb, Croatia. 6 Laboratory for Oxidative Stress, Division of Molecular Medicine, Rudjer Boskovic Institute, Bijeni ka 54, HR-10000 Zagreb, Croatia.*e-mail:nparadj@pfos.hr, tteklic@pfos.hr, mengler@pfos.hr, vcesarus@yahoo.com, hlepedus@yahoo.com, zloncaric@pfos.hr, ivnastolfa@yahoo.com, marotti@irb.hr, mikac@irb.hr, zarkovic@irb.hr Received 13 May 2008, accepted 5 September 2008. Abstract Lettuce is as a world-wide popular leafy vegetable, commonly grown in urban and suburban gardens exposed to the potential risk of soil contamination by intensive and uncontrolled usage of copper-based pesticides. In this research, the physiological response of two lettuce cultivars to excess copper was investigated in controlled conditions, where copper was administered in nutrient solution as 0.5 mM Cu for two days and in an experiment performed outdoors till the lettuce heads formation, using two soils with high total copper content (Cu 120 and 180 mg kg -1 soil). The evaluated parameters were copper accumulation in leaves, lipid peroxidation level, leaf protein and proline content as well as total and specific peroxidase activity. The results indicate similar physiological response mechanisms to copper induced oxidative stress in lettuce grown in different experimental conditions, depending on the severity of stress and cultivar tolerance. Based on the established copper accumulation in lettuce leaves, observed antioxidative activity (GPOX) and increased proline concentration, it could be concluded that the exposure of lettuce plants to excess copper in nutrient medium resulted with altered plant metabolism due to oxidative stress. A short treatment with high copper concentration in nutrient solution resulted in significant difference between cultivars in lipid peroxidation level, showing higher tolerance of cultivar Triatlon that accumulated more copper but had lower TBARS content than cultivar Nadine. Significant correlative relationships between free proline accumulation and peroxidase activity in leaves under influence of copper stress imply possible metabolic connections of enzymatic and non-enzymatic antioxidative response pathways in lettuce. Key words: Copper, guaiacol peroxidase, heavy metal accumulation, lettuce, lipid peroxidation, nutrient solution, oxidative stress, proline, protein content, soil pollution. www.world-food.net Journal of Food, Agriculture & Environment Vol.6 (3&4) : 439-444. 2008 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Introduction Vegetables are vital to the human health and in particular provide the well-known trace elements 1 . Diets rich in fruits and vegetables delay the onset of many age-related diseases and contain a complex mixture of antioxidants but also pro-oxidants, including iron, copper, H 2 O 2 , haem, lipid peroxides and aldehydes 2 . Plants growing on contaminated soils will reflect elevated concentrations of heavy metals in the soils to varying extents, depending on the soil total concentrations, physico-chemical conditions (especially pH) and the genotype of the plant 3 . In general, the inhibition of plant growth and crop production by excess heavy metals such as Cu, Cd, Zn or Ni in contaminated soil was considered as a global agricultural problem 4 . Further investigations are still required to understand the specific role of these pollutants in disturbing the plant metabolism 5 . The major sources of soil contamination with heavy metals are human activities, such as the prolonged application of Cu-based fungicides that was considered as one of the usual causes of high levels of Cu in the soil 6 . Copper is an essential component of electron-transfer reactions, mediated by proteins such as superoxide dismutase, cytochrome-c oxidase and plastocyanin, but the reactivity of copper can lead to the generation of harmful reactive oxygen species 7 . The induction of peroxidases (POX or POD; EC 1.11.1.7) is a general response of higher plants to uptake of toxic amounts of metals 8, 9 . There are some other stress indicators such as proline accumulation, which was considered as important for future investigation on stress thresholds for productivity and product quality of cultivated plants 10 . Lipid peroxidation (TBARS) is also widely used as a biochemical marker for the free radical mediated injury in plant and animal tissues, and the quantification of lipid peroxidation could be a relevant bio-assay for Cu toxicity 11 . Measurement of antioxidants as stress markers will remain an essential aspect in assessing stress responses in plants, but