ISSN 0003-6838, Applied Biochemistry and Microbiology, 2010, Vol. 46, No. 4, pp. 431–437. © Pleiades Publishing, Inc., 2010. Original Russian Text © A.V. Chasov, V.Ya. Alekseeva, O.P. Kolesnikov, F.V. Minibayeva, 2010, published in Prikladnaya Biokhimiya i Mikrobiologiya, 2010, Vol. 46, No. 4, pp. 472–478. 431 INTRODUCTION At present, in consequence of the deterioration of the ecological situation, the contamination of the bio- sphere by various xenobiotics has reached a critical level. To defend themselves from toxic compounds coming in from the environment, plants have a power- ful system of enzymes that cause oxidative degradation of xenobiotics of various chemical structures [1]. First of all, in response to the influence, enzymes localized on the cell surface are activated. A certain connection exists between the resistance of plants to various influ- ences and the state of components of the cell surface, including plasmalemma [2]. The peroxidase and ATPase enzyme systems are the key systems, the activ- ity of which changes when various stressors affect the plant. The functioning of the H + -ATPase together with redox-systems creates and supports the electro- chemical gradient of the proton concentration on plasmalemma. It is known that, apart from the detox- ification of the reactive oxygen species (ROS), perox- idase (POX) also takes part in their formation [3]. ROS can play the role of signal mediators and participate directly in the regulation of the most important bio- logical processes [4, 5]. Xenobiotics, being alien compounds, influence the structure and properties of membranes, and are also capable of modifying the functioning of certain sys- tems of substance transfer [6]. The compounds of the phenothiazine order, chlorpromazine (CP) in particu- lar, which are used in medical practice and possess a strong membranotropic effect, are also currently used as an instrument in studies on adaptation mechanisms of plants [7, 8]. CP is a compound with a wide range of action, capable of suppressing the activity of mem- brane ATPases [9, 10] and inhibiting calmodulin- dependent enzymes [11]. The effect that it has on the membrane varies depending on the concentration [12, 13]. It is known that N,N'-dicyclohexylcarbodi- imide (DCCD), used for modifying the COOH- and SH-groups of proteins, is capable of forming intra- and intermolecular cross-linkages and limiting the mobility of proteins [14]. In addition, it has a colchi- cine-like influence on cytoskeleton [15]. It was shown that, in low concentrations, DCCD interacted covalently with the specific carboxyl group of the F 0 subunit in all studied F 0 F 1 -ATPases [16] and with the specific carboxyl residuum in the preparations of the H + -ATPase isolated from plasma membrane [17, 18]. It was found that diethylstilbestrol (DES) is a powerful F 0 -directed inhibitor of both the membrane-bound and purified mitochondrial F 0 F 1 -ATPases of rat liver [19]. DES, similar to DCCD, inhibits both the ATPase activity and the ATP-dependent transfer of proton in H + -ATPase of plasmalemma of yeast [18], fungi [17], and the ATPase of the plasmalemma of plants [20, 21]. The action of DES on membrane pro- teins is determined by its integration into the lipid- protein membrane complexes or adsorption on the membrane surface [21, 22]. The use of compounds modulating the permeabil- ity of plasmalemma for ions with different degrees of specificity is one of approaches to studying the role of membrane in the regulation of functional responses of cells. The cell response and regulation of physiological processes are determined largely by the structural- Activation of Extracellular Peroxidase of Wheat Roots under the Action of Xenobiotics A. V. Chasov, V. Ya. Alekseeva, O. P. Kolesnikov, and F. V. Minibayeva Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center, Russian Academy of Sciences, Kazan, 420111, Russia e-mail: chasov@mail.knc.ru Received August 3, 2009 Abstract—We studied the influence of xenobiotics of various chemical natures, including N,N'-dicyclohex- ylcarbodiimide, diethylstilbestrol, and chlorpromazine, on the activity of peroxidase, a redox-enzyme that participates in defense reactions of plants. It was shown that the influence of the studied xenobiotics on excised roots of wheat seedlings caused an increase in the permeability of plasmalemma for K + and H + and stimulated the activity of the extracellular peroxidase that forms the superoxide radical anion. It is assumed that the extracellular peroxidase can initiate the transformation of alien compounds on the cell surface, before their entrance into the cells. DOI: 10.1134/S0003683810040125 Abbreviations: ROS—reactive oxygen species, DCCD—N,N'- dicyclohexylcarbodiimide, DES—diethylstilbestrol, POX—per- oxidase, CP—chlorpromazine, ECS—extracellular solution.