EFFECT OF SALT STRESS ON ANTIOXIDANT DEFENCE SYSTEM IN LENTIL (Lens culinaris M.) SEEDLINGS

Bandeoglu, Ebru

Ms., Department of Biochemistry
Supervisor: Prof. Dr. Huseyin Avni Oktem
Co-Supervisor: Prof. Meral Yucel

December, 2001, 100 pages

In this study changes in the activity of antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), ascorbate peroxidase (APX: EC 1.11.1.11) and glutathione reductase (GR: EC 1.6.4.2), cell membrane stability, lipid peroxidation in terms of malondialdehyde (MDA) content, H2O2 content, proline content and physiological changes (as wet-dry weights, root-shoot lengths) of 14 days old lentil (Lens culinaris, Medik. cv. Sultan-1) seedlings subjected to 100 mM and 200 mM NaCl stress for 5 days were studied.
Four SOD isozymes were differentiated in lentil namely Cu/ZnSOD1, Cu/ZnSOD2, FeSOD and MnSOD, FeSOD being only in leaves. Salinity enhanced the activity of Cu/ZnSOD isozymes and the increase was much higher in roots when compared to leaves. MnSOD activity increased only at 200 mM NaCl stress while FeSOD activity decreased at both stress concentrations. Total SOD activity enhanced in both tissues but the increase was more pronounced in roots. APX and GR activity was induced under both salt treatments however a slight decrease in CAT activity was detected in both tissues.
Root-shoot lengths and wet-dry weights significantly decreased by salt treatments. A higher level of lipid peroxidation (MDA content) was observed in leaves when compared to roots at both NaCl stresses. This finding was matched with electrolyte leakage test results in which a significant increase was observed in leaves, while in roots no change was detected.
Proline content increased in both tissues in correlation with increased salt stress. A higher increase was observed in H2O2 content in leaves when compared to roots.
The results obtained suggest that leaves are more susceptible to salt stress. In roots Cu/ZnSOD, APX and proline seem to play an important role in defense against salt stress by effectively removing reactive oxygen species.

Key words: Lentil, salt stress, oxidative stress, SOD, APX, GR, CAT, proline, H2O2, lipid peroxidation, MDA.