ISSN 10214437, Russian Journal of Plant Physiology, 2011, Vol. 58, No. 4, pp. 643–652. © Pleiades Publishing, Ltd., 2011. Published in Russian in Fiziologiya Rastenii, 2011, Vol. 58, No. 4, pp. 558–567. 643 1 INTRODUCTION One of the universal responses of plants to abiotic stress factors (salinity, drought, chilling, heavy metals, etc.) is the accumulation of proline, which is a com patible metabolite with multifunction stressprotec tive properties [1]. In the halophyte Thellungiella sal suginea Mey., the intracellular proline content under salinity may amount to 300 μmol/g dry wt, accounting for almost 80% of the amino acid pool in the cell [2–4]. According to some investigations [2–5], the accumu lation of proline in the plants of Th. salsuginea under stress conditions depends on activation of its biosyn thesis. The proline biosynthesis from glutamate is known to be catalyzed by two enzymes [1, 6]. A key enzyme is Δ 1 pyrroline5carboxylate synthetase (P5CS; EC 2.7.2.11/1.2.1.41), which is encoded by a gene family (P5CS1, P5CS2) [6]. This enzyme cata lyzes the first stage of transformation of glutamate to Δ 1 pyrroline5carboxylate (P5C). During the second stage, P5C is reduced to proline by pyrroline5car 1 This text was submitted by the authors in English. boxylate reductase (P5CR) (EC 1.5.1.2) encoded by the P5CR gene. The proline catabolism depends on proline dehydrogenase (PDH, EC 1.5.99.8), which is encoded by the PDH gene family and catalyzes oxida tion of proline to P5C [1]. Pyrroline5carboxylate dehydrogenase (P5CDH, EC 1.5.1.12) encoded by the gene P5CDH oxidizes P5C to glutamate [1, 7]. The regulation of the key P5CS1 gene transcription under salinity is investigated in details [1, 4, 8]. It is known that transgenic plants of Arabidopsis thaliana L. with stimulated expression of P5CS1 under 35S promoter were more resistant to salinity [8, 9]. It was also shown that the regulation of this gene expression involved ABA [10]. The expression of PDH gene was inhibited under osmotic stress; however, the same as for P5CS1 gene, information about its expression under oxidative stress is scarce. Some works [11, 12] have shown that under salinity the greater part of proline produced de novo is accu mulated in the cytoplasm, which points to its osmo regulatory function. However, the elevation of proline content in plants also occurs in response to other stress factors that do not always upset the osmotic balance. It is known that all the damaging abiotic factors induce generation of surplus reactive oxygen species (ROS) in plant cells. Currently, the elevation of ROS content in RESEARCH PAPERS Regulation of Gene Expression Governing Proline Metabolism in Thellungiella salsuginea by NaCl and Paraquat 1 N. L. Radyukina, Yu. V. Ivanov, A. V. Kartashov, P. P. Pashkovskiy, N. I. Shevyakova, and Vl. V. Kuznetsov Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya ul. 35, Moscow, Russia; fax: +7 (499) 9778018; email: natrad@yandex.ru Received December 24, 2010 Abstract—Differential expression of the proline metabolism genes in Thellungiella salsuginea (Pall) E. Schulz was investigated under salinity (100 and 300 mM NaCl), upon the effect of paraquat (0.1 μM), and at their joint action. It was shown that, depending on the intensity of stress factor, expression of the P5CS1 gene was induced in the leaves (at 100 mM NaCl) or roots (at 300 mM NaCl). When the plants on control medium were treated with paraquat, the proline content changed only in the leaves. Time course of proline content in the leaves complied with the dynamic of P5CS1 gene expression, while expression of PDH gene essentially did not change. When the plants, which experienced salt stress, were treated with paraquat, the content of proline and the P5CS1 mRNA level increased even more. The obtained results suggest a complicated nature of signaling between the organs of the halophyte Th. salsuginea causing expression of the proline biosynthesis genes in the leaves and roots under the effect of salinity, paraquat, or upon their joint action. The proline catabolism in these plants was maintained essentially unchanged, which is probably related to the participation of proline and/or the products of its degradation in the pathways of other metabolite biosynthesis. We suggested that proline took part in ROS scavenging process and proline level was under strong control in Th. salsuginea. Keywords: Thellungiella salsuginea, proline, gene expression, oxidative stress, salinity. DOI: 10.1134/S102144371104011X Abbreviations: P5CS1—pyrroline5carboxylate synthetase1; PDH—proline dehydrogenase; P5CR pyrroline5carboxylate reductase; P5CDH—pyrroline5carboxylate dehydrogenase.