Ismail Turkan

The effect of salt stress on lipid peroxidation and antioxidants in leaves of sugar beet Beta vulgaris L. and wild beet Beta maritima L.

Abstract The changes in lipid peroxidation and the possible involvement of the antioxidant system in relation to the tolerance to salt stress was investigated in the cultivated beet Beta vulgaris L. cv. ansa and its wild salt-tolerant relative Beta maritima TR 51196 . The 40 days old beet seedlings were subjected to 0, 150 and 500 mM NaCl for 12 days. In B. maritima constitutive level of lipid peroxidation was lower, but activities of superoxide dismutase (SOD), peroxidase (POX), ascorbate peroxidase (APOX), catalase (CAT) and glutathione reductase (GR) were inherently higher than in B. vulgaris cv. ansa . Compared to B. vulgaris , lipid peroxidation was also lower and the activities of SOD, POX, APOX, CAT and GR were higher in B. maritima at 150 and 500 mM NaCl. These results possibly suggest that the wild salt-tolerant beet, B. maritima exhibit a better protection mechanism against oxidative damage by maintaining a higher inherited and induced activity of antioxidant enzymes than the relatively sensitive plants of the sugar beet, B. vulgaris cv. ansa .

Effects of 24-epibrassinolide on seed germination, seedling growth, lipid peroxidation, proline content and antioxidative system of rice (Oryza sativa L.) under salinity stress

The effects of 24-epibrassinolide (24-epiBL) on seedling growth, antioxidative system, lipid peroxidation, proline and soluble protein content were investigated in seedlings of the salt-sensitive rice cultivar IR-28. Seedling growth of rice plants was improved by 24-epiBL treatment under salt stress conditions. When seedlings treated with 24-epiBL were subjected to 120 mM NaCl stress, the activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6) and glutathione reductase (EC 1.6.4.2) did not show significant difference, whereas the activity of ascorbate peroxidase (EC 1.11.1.11) significantly increased. Increased activity of peroxidase (EC 1.11.1.7) under NaCl stress showed remarkable decrease in the 24-epiBL+NaCl-applied group. Lipid peroxidation level significantly increased under salt stress but decreased with 24-epiBL application revealing that less oxidative damage occurred in this group (24-epiBL+NaCl). In addition, increased proline content in the NaCl-applied group was decreased by 24-epiBL application in the 24-epiBL+NaCl-applied group. Soluble protein content was increased by 24-epiBL application even under NaCl stress, being also higher than control conditions (no 24-epiBL or NaCl treatment). 24-epiBL treatment considerably alleviated oxidative damage that occurred under NaCl-stressed conditions and improved seedling growth in part under salt stress in sensitive IR-28 seedlings.

Reactive oxygen species regulation and antioxidant defence in halophytes

Production of reactive oxygen species (ROS), which are a by-product of normal cell metabolism in living organisms, is an inevitable consequence of aerobic life on Earth, and halophytes are no exception to this rule. The accumulation of ROS is elevated under different stress conditions, including salinity, due to a serious imbalance between their production and elimination. These ROS are highly toxic and, in the absence of protective mechanisms, can cause oxidative damage to lipids, proteins and DNA, leading to alterations in the redox state and further damage to the cell. Besides functioning as toxic by-products of stress metabolism, ROS are also important signal transduction molecules in controlling growth, development and responses to stress. Plants control the concentrations of ROS by an array of enzymatic and non-enzymatic antioxidants. Although a relation between enzymatic and non-enzymatic antioxidant defence mechanisms and tolerance to salt stress has been reported, little information is available on ROS-mediated signalling, perception and specificity in different halophytic species. Hence, in this review, we describe recent advances in ROS homeostasis and signalling in response to salt, and discuss current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses in halophytes. We also highlight the role of genetic, proteomic and metabolic approaches for the successful study of the complex relationship among antioxidants and their functions in halophytes, which would be critical in increasing salt tolerance in crop plants.

Effect of salt stress on lipid peroxidation and superoxide dismutase and peroxidase activities of Lycopersicon esculentum and L. pennellii

In this study, a relationship between lipid peroxidation, the antioxidant defense system and salt stress in salt-sensitive cultivated tomato (Lycopersicon esculentum) and its salt-tolerant wild relative (L. pennellii) was established. Superoxide dismutase (SOD) activities were significantly higher in the leaves of L. pennellii than those of L. esculentum after 12 and 84 d. POX activity showed a gradual increase in both cultivars under 70 mM NaCl. POX activity in L. pennellii significantly increased after 6 and 84 d whereas showed no remarkable change in leaves of L. esculentum under 140 mM NaCl. A higher salinity tolerance of L. pennellii was also correlated with a lower lipid peroxidation, which might be due to a higher content of antioxidant enzymes studied.

Redox- and Reactive Oxygen Species-Dependent Signaling into and out of the Photosynthesizing Chloroplast

The photosynthesizing chloroplast functions as a conditional source of redox and ROS information which tunes processes inside the chloroplast and hence impacts on signaling events in the cytosol and nucleus. Photosynthesis is a high-rate redox metabolic process that is subjected to rapid changes in input parameters, particularly light. Rapid transients of photon capture, electron fluxes, and redox potentials during photosynthesis cause reactive oxygen species (ROS) to be released, including singlet oxygen, superoxide anion radicals, and hydrogen peroxide. Thus, the photosynthesizing chloroplast functions as a conditional source of important redox and ROS information, which is exploited to tune processes both inside the chloroplast and, following retrograde release or processing, in the cytosol and nucleus. Analyses of mutants and comparative transcriptome profiling have led to the identification of these processes and associated players and have allowed the specificity and generality of response patterns to be defined. The release of ROS and oxidation products, envelope permeabilization (for larger molecules), and metabolic interference with mitochondria and peroxisomes produce an intricate ROS and redox signature, which controls acclimation processes. This photosynthesis-related ROS and redox information feeds into various pathways (e.g. the mitogen-activated protein kinase and OXI1 signaling pathways) and controls processes such as gene expression and translation.

Comparison of ROS formation and antioxidant enzymes in Cleome gynandra (C4) and Cleome spinosa (C3) under drought stress

Differences between antioxidant responses to drought in C(3) and C(4) plants are rather scanty. Even, we are not aware of any research on comparative ROS formation and antioxidant enzymes in C(3) and C(4) species differing in carboxylation pathway of same genus which would be useful to prevent other differences in plant metabolism. With this aim, relative shoot growth rate, relative water content and osmotic potential, hydrogen peroxide (H(2)O(2)) content and NADPH oxidase (NOX) activity, antioxidant defence system (superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR) enzymes and their isoenzymes), CAT1 mRNA level, and lipid peroxidation in seedlings of Cleome spinosa (C(3)) and Cleome gynandra (C(4)) species of Cleome genus exposed to drought stress for 5 and 10 day (d) were comparatively investigated. Constitutive levels of antioxidant enzymes (except SOD) were consistently higher in C. spinosa than in C. gynandra under control conditions. CAT1 gene expression in C. spinosa was correlated with CAT activity but CAT1 gene expression in C. gynandra at 10 d did not show this correlation. Drought stress caused an increase in POX, CAT, APX and GR in both species. However, SOD activity was slightly decreased in C. gynandra while it was remained unchanged or increased on 5 and 10 d of stress in C. spinosa, respectively. Parallel to results of malon dialdehyde (MDA), H(2)O(2) content was also remarkably increased in C. spinosa as compared to C. gynandra under drought stress. These results suggest that in C. spinosa, antioxidant defence system was insufficient to suppress the increasing ROS production under stress condition. On the other hand, in C. gynandra, although its induction was lower as compared to C. spinosa, antioxidant system was able to cope with ROS formation under drought stress.

Endoplasmic reticulum stress triggers ROS signalling, changes the redox state, and regulates the antioxidant defence of Arabidopsis thaliana

Summary Endoplasmic reticulum stress, which is induced by tunicamycin, triggers reactive oxygen species signalling via NADPH oxidase activity and also regulates the antioxidant defence system in Arabidopsis thaliana.

Comparison of moss and bark samples as biomonitors of heavy metals in a highly industrialised area in Izmir, Turkey

The moss, Hypnum cupressiforme and bark of the pine, Pinus brutia have been used for passive monitoring of airborne heavy metal pollution by an iron-steel mill of an industrialised area of Izmir, Turkey. Six metals, lead (Pb), cadmium (Cd), zinc (Zn), chromium (Cr), manganese (Mn) and iron (Fe) have been monitored using atomic absorption spectrometry. Between 26.2.1992 and 13.8.1992 samples were taken on five occasions at a distance of 0.25, 1.0 and 2.5 km from the mill. The results show an accumulation of all six metals, with differences between the moss and bark samples and a decrease in concentration with distance from the mill. The arithmetic means of the measured heavy metal concentrations in the moss, Hypnum cupressiforme, were always much higher than those in the bark of the P. brutia, indicating that the moss H. cupressiforme is more suitable than the bark of P. brutia for use in monitoring heavy metal pollution. The results show that the study area, within 2.5 km from the iron-steel mill, is heavily polluted.

Antioxidant responses of chickpea plants subjected to boron toxicity

This study investigated oxidative stress and the antioxidant response to boron (B) of chickpea cultivars differing in their tolerance to drought. Three-week-old chickpea seedlings were subjected to 0.05 (control), 1.6 or 6.4 mm B in the form of boric acid (H(3)BO(3)) for 7 days. At the end of the treatment period, shoot length, dry weight, chlorophyll fluorescence, B concentration, malondialdehyte content and the antioxidant enzymes superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were measured. The 1.6 mm B treatment did not cause significant changes in shoot length of cultivars, although shoot length increased in the drought-tolerant Gökce and decreased in the drought-sensitive Küsmen after 6.4 mm B treatment. Dry weights of both cultivars decreased with 6.4 mm B treatment. Chlorophyll fluorescence (Fv/Fm) did not change in Gökce at either B level. Nor did it change in Küsmen with 1.6 mm B but Fv/Fm decreased with 6.4 mm B. Boron concentration in the shoots of both cultivars increased significantly with increasing levels of applied B. Significant increases in total SOD activity were observed in shoots of both cultivars given 1.6 and 6.4 mm B. Shoot extracts exhibited five activity bands, two of which were identified as MnSOD and Cu/ZnSOD. In comparison to the control group, all enzyme activities (except APX and SOD) decreased with 1.6 mm B stress. GR activity decreased, while activities of CAT, POX and APX did not change with 6.4 mm B in Küsmen. On the other hand, activities of CAT, APX and SOD increased in Gökce at both B levels. In addition, lipid peroxidation was higher in Küsmen than in Gökce, indicating more damage by B to membrane lipids in the former cultivar. These results suggest that (i) Gökce is tolerant and Küsmen is sensitive to B, and (ii) B tolerance of Gökce might be closely related to increased capacity of the antioxidative system (total SOD, CAT and APX) to scavenge reactive oxygen species and thus suppress lipid peroxidation under B stress. To the best of our knowledge, this is the first report on the antioxidant response of chickpea seedlings to B toxicity.

Elucidation of physiological and biochemical mechanisms of an endemic halophyte Centaurea tuzgoluensis under salt stress.

In this study, physiological and biochemical responses of Centaurea tuzgoluensis, a Turkish endemic halophyte, to salinity were studied. Therefore, the changes in shoot growth, leaf relative water content (RWC), ion concentrations, lipid peroxidation, hydroxyl (OH·) radical scavenging activity, proline (Pro) content, and antioxidant system [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR)] were investigated. The 60 days (d) old C. tuzgoluensis seedlings were subjected to 0, 150 and 300 mM NaCl for 7 d and 14 d. The relative shoot growth was generally did not change in the 150 mM NaCl, but reduced with 300 mM NaCl stress at 7 d and 14 d. RWC was higher in 150 mM NaCl-treated leaves than that of 300 mM NaCl. Salinity decreased K⁺/Na⁺ ratio, but increased Na⁺, Cl⁻, Ca⁺² and Na⁺/Cl⁻ ratio in the leaves. On the other hand, it did not change or increase the K⁺ content at 150 and 300 mM NaCl, respectively. MDA content in the 150 and 300 mM NaCl-treated leaves remained close to control at 7 d. This was related to enhanced activities of SOD, CAT, APX and GR enzymes, and their isoenzymes especially Fe-SOD in the leaves. On the other hand, the higher sensitivity to 300 mM NaCl at 14 d was associated with inadequate increase in antioxidant enzymes and the decreased OH radical scavenging activity. All these results suggest that C. tuzgoluensis has different antioxidant metabolisms between short- (7 d) and long-term (14 d) salt treatments and salinity tolerance of C. tuzgoluensis might be closely related to increased capacity of antioxidative system to scavenge reactive oxygen species (ROS) and accumulation of osmoprotectant proline under salinity conditions.