Analele �tiin�ifice ale Universit��ii „Alexandru Ioan Cuza”, Sec�iunea Genetic� �i Biologie Molecular�, TOM XII, 2011 RESEARCH REGARDING THE DYNAMICS OF SOME BIOCHEMICAL MARKERS OF OXIDATIVE STRESS AT MONILINIA LAXA (ADRH. & RUHL.) HONEY CULTIVATED ON DIFFERENT AMINO ACIDS ENRICHED MEDIA ELENA CIORNEA 1* , ELENA TUTU 1 , SABINA IOANA COJOCARU 1 Keywords: amino acids, Monilinia laxa , catalase, peroxidase, oxidative stress Abstract: Antioxidants that make up the defense for Ascomycetes still arouses a major interest because of their hypothetical role as virulence and aggression factors and also as the enzymes that play a key role in cellular defense against ROS produced during microbial metabolic activity. A study of catalase and peroxidase activity dynamics of the species Monilinia laxa (Aderh & Ruhl.) Honey cultivated in vitro on medium supplemented with different amino acids was conducted in order to know the biology of the fungi responsible for the appearance of brown rot at various species of stone fruits. We used for this purpose the Leonian medium (in the formula changed by Bonnar), in each variant being added 0, 125 mg of the following amino acids: alanine, glutamic acid, asparagine, aspartic acid, cystine, cysteine, phenylalanine, histidine, valine, lysine, serine, methionine and leucine. We also used a control variant, without amino acids, in final resulting 14 working versions. To determine the catalase activity Sinha method was used, to monitor the peroxidase activity we used Möller method and the experimental measurements carried out at two intervals, were made both of fungus mycelium and culture fluid. We found notable differences in the activity of two enzymes, microbial culture induced both by the age of the culture medium and the type of amino acid introduced in it. INTRODUCTION Ubiquitous organisms, filamentous fungi have a high adaptive plasticity to different environmental changes, one of the fundamental requirements of these microorganisms for surviving is the need to adjust their activities in terms of an aerobic lifestyle, as the metabolic performance in such circumstances is followed by the emergence of reactive oxygen species and, hence, the need for it`s proper management, its absence can lead toward apoptosis and death of eukaryotic cell due to so-called oxidative stress (Avery, S.V. et al., 2008). Defined as being an imbalance between reactive oxygen species production and the biological system`s ability of rapid detoxification, followed by the repair and removal of damaged parts resulting from their activity, oxidative stress is characterized by disturbances in the normal redox state of the cells, capable of causing toxic effects by peroxides and free radicals production, equipped to destroy cellular components, including proteins, lipids and DNA (Sies, H., 1991, Dean R.T. et al., 1997, Esser, K. and Kues, U., 2006) . The ways in which organisms are protected from the aggression of reactive oxygen species are related to cell compartmentalisation, to the ability to elaborate adaptive responses inducible in oxidative stress conditions, to repair and turnover processes that help to minimize the damage that occures from reactive oxygen species attack or by the existence of hydroxyl radical scavenger that captures a series of hidroxil radicals, superoxides and organic radicals, which chelate metal ions and prevent certain chemical reactions toxic for the organism, the so-called preventive antioxidants (Gadd, G.M., 2001) and, last but not least, the protection afforded by antioxidant compounds and enzyme systems. The protective enzyme system of eukaryotic cells include: superoxide dismutase, catalase, glutathione peroxidase, glutathione transferase, glutathione reductase and glucose-6-phosphate dehydrogenase, these enzymes having a predominantly intracellular localization, the extracellular environment being more exposed to radical attack (Bai, Z. et al., 2003, Li, Q. et al., 2009). Present in the medium, some amino acids regulate the activity of fungal enzymes, including the oxidoreductases (Subramanian, K.N. et al., 1968), data from literature indicating that interference between amino acids and the medium are responsible for the catalase inhibition, and the presence of arginine in the culture medium inhibits the catalase activity (Frederick, J.R. et al., 2001). Also, experimental studies show the ability of oxidative decarboxylation of some amino acids such as serine, alanine, phenylalanine, tryptophan and methionine. In the presence of dihydrofumarate, this oxidoreductase catalyzes the hydroxylation of various aromatic compounds and reduces nitrate in the presence of some specific donors (Fear, 1976, quoted by Ro�u, C.M., 2007). In vitro experiments showed that the activity and the thermostability of peroxidase depend, in many cases, by their interaction with amino acids such as proline, tryptophan, valine, �-alanine (Bakardjeva, N. et al., 1999). Shtarkman, I.N. et al, 2007 demonstrated that some amino acids present in the medium (methionine, cystine, tyrosine, tryptophan, phenylalalnine, lysine, leucine, arginine and proline) are responsible for protecting the intracellular DNA against damage caused by reactive oxygen species under a moderate oxidative stress, complementing the antioxidant enzyme defense system activity in the eukaryotic cells. Same authors complete the recent studies that aimed the research on the formation of reactive oxygen species in aqueous solutions, indicating that vary physical factors makes these mediums chemical reactive, the biological molecules, 109