Romanian Biotechnological Letters Vol. 17, No.3, 2012 Copyright © 2012 University of Bucharest Printed in Romania. All rights reserved ORIGINAL PAPER 7227 Effects of long-term salt stress on antioxidant system, chlorophyll and proline contents in pea leaves Received for publication, January 10, 2010 Accepted, June 11, 2011 LOKMAN OZTURK 1 , YAVUZ DEMIR* 2 , ALI UNLUKARA 3 , ILHAMI KARATAS 1 , AHMET KURUNC 4 AND ORAL DUZDEMIR 5 1 Department of Biology, Faculty of Arts and Sciences, Gaziosmanpasa University, 60250- Tokat, Turkey 2 Department of Biology, Faculty of Education, Atatürk University, 25240-Erzurum, Turkey. 3 Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Erciyes University, 38039-Kayseri, Turkey 4 Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Akdeniz University, 07058-Antalya, Turkey 5 Vocational School, Karatekin University, 18100-Çankırı, Turkey Abstract The effects of long-term salt stress on the contents of chlorophyll, proline, protein, hydrogen peroxide (H 2 O 2 ), and malondialdehyde (MDA) in terms of lipid peroxidation, and on the changes in activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) in leaves of pea (Pisum sativum cv Rona) were investigated in field conditions. Salinity and irrigation water regime experiments were set up in pots as randomized plot experimental designs with five replications. The experiment focused on pea responses to irrigation water salinity by irrigating the crops using 6 different levels of saline water (0.7, 2.0, 3.0, 4.0, 5.0 and 7.0 dS m -1 ) with a constant leaching fraction (LF = 0.30). The pots were located in the experimental area under a polyethylene cover which was about 1.8 m height from the surface for the purpose of eliminating rainfall effect on the experiments. Chlorophyll and protein contents were significantly decreased while accumulation of proline was enhanced with increased electrical conductivity (EC). Both MDA and H 2 O 2 contents were reduced in the result of high salts application. All of the salt treatments increased total SOD activity significantly, as a remarkable increase in POD activity was observed especially at 5.0 and 7.0 dS/m EC. CAT and APX activities generally decreased in salt stressed seedlings. Our study indicates that its acquisition of salt tolerance may be a consequence of improved resistance to oxidative stress via increased activities of peroxidase and the superoxide dismutase/ascorbate-glutathione cycle. Key words: Antioxidant Enzyme, Pea, Proline, Salinity, MDA, H 2 O 2 . Abbrevations: EDTA, Ethylenediaminetetraacetic acid; PVPP, polyvinyl polypirrolidone, Introduction Salinity in the soil and irrigation water is an environmental problem and a major constraint for crop production. Salt stress (NaCI) in plants influences some basic plant metabolic processes such as, photosynthesis, protein synthesis, and energy and lipid metabolism [1]. Salt stress (NaCl) has both osmotic (cell dehydration) and toxic (ion accumulation) effects on plant cells, impairing growth, ion homeostasis, photosynthesis and nitrogen fixation among other key physiological processes. Nowadays, several markers of stress have been measured to assess the physiological status of the plants [1]. These include proline and soluble protein contents, photosynthetic pigments and metabolic products of oxidative damage. In addition to other environmental stresses, salt stress also causes oxidative damage, thereby affecting cellular membrane integrity, enzyme activities, and functioning of