Effects of long-term salt stress on antioxidant system, chlorophyll and proline contents in pea leaves

The effects of long-term salt stress on the contents of chlorophyll, proline, protein, hydrogen peroxide (H2O2), 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 H2O2 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.