The role of antioxidant defense systems at differential salt tolerance of Hordeum marinum Huds. (sea barleygrass) and Hordeum vulgare L. (cultivated barley)

Abstract

Barley ( Hordeum vulgare), one of the world's most extensively cultivated crops, is regarded as salt tolerant compared with other Triticeae members. There are also differences in salt tolerance between barley species. Hordeum marinum (sea barleygrass) inhabiting salt marshes is regarded as being markedly more salt tolerant than H. vulgare (cultivated barley). Moreover, it has been considered one of the most important wild species of barley in terms of having a source of genes for improvement of salt tolerance of wheat. The role of osmoregulation and ion homeostasis on salt tolerance of H. marinum has already been reported. However, the role of antioxidant defense system on salt tolerance of H. marinum has not been addressed yet. Therefore, in the present study, we investigated the changes in the lipid peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR)] and isoenzymatic profiles of some antioxidant enzymes (SOD, APX, GR) in H. marinum and H. vulgare cv. Tokak 157/37, comparatively. H. marinum and H. vulgare were subjected to 0, 150 and 300 mM NaCl stress for 7 days. Shoot FW (fresh weight) and DW (dry weight) of both species were decreased at 300 mM NaCl, being more pronounced in H. vulgare. Shoot RGR (relative growth rate) of H. vulgare was more sensitive to NaCl than H. marinum. Similarly, stomatal conductance ( g s) was also reduced in both species by salt treatment, but it was more pronounced in H. vulgare. Salt treatment had no effects on chlorophyll fluorescence (Fv/Fm) in both species. Peroxidation of lipid membranes showed no change in H. marinum under salt stress while it increased by 60% in H. vulgare at 300 mM NaCl. At 150 mM NaCl, the activities of all antioxidant enzymes (except SOD) increased in both species. However, the activities of some antioxidant enzymes and their isoenzymes in H. vulgare either remained unchanged (CAT, POX and APX) or even decreased (SOD, GR) at 300 mM NaCl. Nevertheless, the activities of all antioxidant enzymes of H. marinum increased significantly at 300 mM NaCl. Moreover, while new isoenzymes (APX5, GR5) were identified in H. marinum, intensities of some isoenzymes (APX1, 2, 6, 7 and GR1, 3, 6, 7) increased at 300 mM NaCl. These findings possibly suggest that H. marinum has a better protection mechanism against salt-induced oxidative damage than H. vulgare, by inducing activity of antioxidant enzymes and their isoenzymes.