Lipid peroxidation and changes in the activity of superoxide dismutase caused by water deficit in basil (Ocium basilicum L.) and savory (Satureja hortensis L.) By K. INOTAI 1 * , P. RADÁCSI 1 , P. CZÖVEK 2 , SZ. SÁROSI 1 , M. LADÁNYI 3 and É. NÉMETH 1 1 Department of Medicinal and Aromatic Plants, Corvinus University of Budapest, Villányi Str. 29-43, Budapest 1118, Hungary 2 Department of Plant Physiology and Molecular Plant Biology, Eötvös Loránd University, Pázmány Péter sétány 1/C, Budapest 1117, Hungary 3 Department of Mathematics and Informatics, Corvinus University of Budapest, Villányi Str. 29-43, Budapest 1118, Hungary (e-mail: katalin.inotai@uni-corvinus.hu) (Accepted 18 April 2012) SUMMARY Two aromatic species (Ocimum basilicum L. and Satureja hortensis L.) with different water requirements were submitted to varying water supply, as characterised by different soil water capacities [SWC; control (C), 70% SWC; Stress 1 (S1), 50% SWC; and Stress 2 (S2), 30% SWC] in a growth chamber. The effect of water deficit on the formation of malondialdehyde (MDA), a product of lipid peroxidation (LPO), and on superoxide dismutase (SOD) activity were evaluated at three phenological phases (before flowering, at full-flowering, and after flowering) in both plant species. The results revealed that MDA contents were significantly higher in savory than in basil. However, significant increases in MDA contents, as a consequence of changes in the water supply, were detected only in basil (by 23% and 49% in S1 and S2, respectively). In contrast, SOD activities in control plants showed similar values in both species. Elevated SOD activities were detected in basil and in savory as a reaction to water deficit stress, with maximum SOD activities occurring during full-flowering (3.212 Units mg –1 protein and 2.655 Units mg –1 protein in basil and savory, respectively). We conclude that water deficit stress (to 50% or 30% SWC) may result in increased SOD activities, which were responsible for the decreased levels of superoxide free radicals in both species examined. However, under the conditions used here, enhanced LPO was detectable only in basil, known as a plant with a high water requirement. W ater is a pre-requisite for life on Earth, and determines the distribution and production of all plant species. As a consequence of water deficit, deleterious changes in photosynthesis, membrane stability, and mitochondrial respiration may be observed (Almeselmani et al., 2006). Due to the closure of leaf stomata and decreased CO 2 intake, a direct blockage of photosynthesis and increased formation of reactive oxygen species (ROS) may occur under water deficit stress (Smirnoff, 1993). Generally, during respiration in the mitochondria, O 2 is reduced to water by the incorporation of electrons. However, under stress situations, energy-consuming processes are accelerated, and this reaction is inhibited due to blockage of the electron-releasing capacity of the electron transport chain. The reduced supply of electrons then leads to the formation of superoxide-anions (Sutherland, 1991). Even under optimal environmental circumstances, a low level of ROS are formed continuously in the mitochondria, chloroplasts, and peroxisomes.These ROS are normally eliminated by the anti-oxidative protection mechanisms of the cell. However, under conditions of water deficit, the balance between the formation and the scavenging of ROS is disturbed (Ozden et al., 2009). As a consequence, increasing intracellular levels of ROS may be detected, while nucleic acids, lipids, and proteins may be damaged, thus losing their biological functions. Evidence shows that stress conditions can cause membrane degradation and cellular damage (Gill and Tuteja, 2010). One of the most commonly detected outcomes of membrane degradation is lipid peroxidation (LPO), which results in a severe decrease or loss of ion- selective permeability. During LPO, the development of hydroxyl radicals (OH • ) can be detected which then attack the side-chains of unsaturated fatty acids in the membrane. Malondialdehyde (MDA) arises as a product of the peroxidation of (18:3) linolenic acid. MDA is one of the most reactive aldehydes (Yamauchi et al., 2008). Several enzymes [superoxide dismutase (SOD); ascorbate peroxidase (APOX); glutathione reductase (GR), and catalase (CAT)] and many non-enzymatic antioxidants (e.g., glutathione, ascorbic acid, - tocopherol, and carotenoids) take part in the elimination of ROS (Sairam et al., 2000). However, among these, only SOD reacts directly with the superoxide anion (O 2 •– ). H 2 O 2 is formed as a result of this reaction, which is further scavenged by CAT and various peroxidase enzymes. Accepted methods by which to estimate the extent of oxidative stress include determinations of MDA content, *Author for correspondence. Journal of Horticultural Science & Biotechnology (2012) 87 (5) 499–503