Hulya Turk

Modulation of alternative oxidase to enhance tolerance against cold stress of chickpea by chemical treatments

The alternative oxidase (AOX) is the enzyme responsible for the alternative respiratory pathway. This experiment was conducted to examine the influence on cold tolerance ability of chickpea (Cicer aurentium cv. Müfitbey) seedlings of AOX activator (pyruvate), AOX inhibitor (salicylhydroxamic acid (SHAM)) and an inhibitor of the cytochrome pathway of respiration (antimycin A) treatments. 5mM pyruvate, 2μM antimycin A and 4mM SHAM solutions were exogenously applied to thirteen-day-old chickpea leaves and then the seedlings were transferred to a different plant growth chamber arranged to 10/5°C (day/night) for 48h. Cold stress markedly increased the activities of antioxidant enzymes compared to controls. Pyruvate and antimycin A significantly increased the cold-induced increase in antioxidant activity but SHAM decreased it. Cold-induced increases in superoxide anion, hydrogen peroxide, and lipid peroxidation levels were significantly reduced by pyruvate and antimycin A, but increased by SHAM treatment. Pyruvate and antimycin A application increased both the activity and protein expression of AOX in comparison to cold stress alone. However, SHAM significantly decreased activity of AOX but did not affect its expression. Total cellular respiration values (TCRV) supported the changes in activity and expression of AOX. While TCRV were increased by cold and pyruvate, they were significantly reduced by SHAM and especially antimycin A. These results indicate that pyruvate and antimycin A applications were effective in reducing oxidative stress by activating the alternative respiratory pathway as well as antioxidant activity. Furthermore, direct activation of AOX, rather than inhibition of the cytochrome pathway, was the most effective way to mitigate cold stress.

Effects of progesterone application on antioxidant enzyme activities and K+/Na+ ratio in bean seeds exposed to salt stress

This study aimed to investigate the influence of progesterone, a mammalian sex hormone, on germination of bean (Phaseolus vulgaris L.) seeds exposed to salt stress. The exogenous addition of 10−6, 10−8 and 10−10 M progesterone to the stressing media in which bean seeds were germinated in combination with the salt (100 mM NaCl) stressor induced significant protective changes in the germination and early growth parameters. The mitigating effect of progesterone was evaluated by the measurement of radicle and plumule lengths, activities of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT). In addition, it is the first study that exhibited changes in K/Na ratio. The obtained results showed that progesterone application stimulated germination and growth of salt-stressed seeds. Similarly, it stimulated significantly SOD, POX and CAT activities compared to both control and salt control. Salt stress significantly increased the lipid peroxidation compared to the control seeds. However, parallel to the increase in antioxidant activity, lipid peroxidation was significantly reduced by progesterone application. The best stimulatory effects on investigated parameters were recorded at 10−8 M progesterone-applied seeds. On the other hand, salt stress reduced remarkably K/Na ratio by 50% in radicle and by 80% in plumule. However, progesterone application significantly mitigated the reduction in K/Na ratio. These findings clearly demonstrate that progesterone has a positive role in moderate detrimental effects induced by salt.

The availability of bone powder as inorganic element source on growth and development in wheat seedlings.

Bone powder (BP), a by-product of cattle slaughtering plants, consists of fat, protein, amino acids, inorganic elements and vitamins. It is used as bone meal in biomedical and feed industry because of its rich content. In addition, bone contains a large amount of inorganic elements especially calcium (Ca) and phosphorus (P), which the plants need to maintain their physiological and biochemical processes. BP has been used as Ca and P source in agriculture for many years; however, its effects on plant growth and development have not yet been studied in detail. The present study aimed to determine the effects of BP on dry weight and contents of total chlorophyll, soluble protein and sugar as indicators of physiological response in the leaves. For this purpose, bone powder solutions (BPS) were prepared at different concentrations (0.5%, 1%, 1.5% and 2%) and applied to growing media of the 10-day wheat seedlings. Afterward, the 14-day seedlings were harvested, and the effects of BPS on plant response were determined. The results showed that BPS treatments significantly stimulated dry weight and contents of total chlorophyll, protein and sugar compared to control seedlings. The best stimulatory effect of BPS was determined at 1% concentration. According to these results, it is possible to say that BP may be used to meet the inorganic element requirements of plants in poor soils and hydroponic systems.

Attenuation of lead toxicity by promotion of tolerance mechanism in wheat roots by lipoic acid

This study was performed to determine the possible ameliorative effect of alpha-lipoic acid (LA) against oxidative stress evoked by lead (Pb) toxicity on 5-d wheat seedlings and elucidate how this ameliorative process was mediated. Pb toxicity caused a significant reduction in early seedling growth as evidenced by stunted root and coleoptile growth. To cope with the Pb toxicity, the activities of antioxidant enzymes were significantly stimulated compared to the control. However, in spite of high activities of these enzymes, contents of reactive oxygen species (ROS), superoxide anion and hydrogen peroxide and lipid peroxidation level were significantly high compared with the control. Similarly, Pb toxicity caused a marked decrease in the level of reduced forms of ascorbate and glutathione and thus it changed their reduced/oxidized ratio in favor of oxidized forms. On the other hand, LA supplementation further promoted uptake, accumulation, and transportation of Pb by stimulating tolerance mechanism involving ion uptake/accumulation at a high level. Moreover, ROS content and lipid peroxidation level were recorded as lower than that of the stressed-ones alone. In addition, while Pb toxicity markedly reduced amylase activity by decreasing Ca2+ content in endosperms, LA supplementation mitigated the reduction in amylase activity by increasing Ca2+ content. The changes in amylase activity were supported by isozymes patterns. Taken together, LA carried out its ameliorative effect against Pb toxicity via stimulation of tolerance mechanism, and this mechanism was linked to regeneration of the other main antioxidant compounds due to its own antioxidant property instead of activation of antioxidant enzymes.

Regulation of ion homeostasis by aminolevulinic acid in salt-stressed wheat seedlings

Salinity is regarded as a worldwide agricultural threat, as it seriously limits plant development and productivity. Salt stress reduces water uptake in plants by disrupting the osmotic balance of soil solution. In addition, it creates a damaged metabolic process by causing ion imbalance in cells. In this study, we aim to examine the negative effects of 5-aminolevulinic acid (ALA) (20 mg/l) on the ion balance in wheat seedling leaves exposed to salt stress (150 mM). Sodium is known to be highly toxic for plant cells at high concentrations, and is significantly increased by salt stress. However, it can be reduced by combined application of ALA and salt, compared to salt application alone. On the other hand, while the K+/Na+ ratio was reduced by salt stress, ALA application changed this ratio in favor of K+. Manganese, iron, and copper were also able to reduce stress. However, ALA pre-treatment resulted in mineral level increments. Conversely, the stress-induced rise in magnesium, potassium, calcium, phospho...

Estrone induced biochemical and molecular changes confers tolerance to boron toxicity in wheat seedlings

To determine the effects of estrone on the ability of plants to tolerate boron toxicity, estrone (0.01 μM) and boron (5 mM H3BO3), singly or in combination, were exogenously applied to 11-d-wheat seedlings and 3 days later from treatments, they were harvested to determine many parameters. Boron toxicity caused to remarkable reductions on the root and shoot lengths. Besides, it led to a marked decrease in the activities of antioxidant enzymes, including superoxide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), as well as an decrease in the level of soluble protein and photosynthetic pigments including chlorophyll and carotene. Thus, boron toxicity bring about a significant oxidative injury by increasing levels of the superoxide anion (O2 -.), hydrogen peroxide (H2O2) and malondialdehyde (MDA). Whereas estrone was able to reduce the boron-induced oxidative damage and improved the antioxidant system. Moreover, the effects of boron toxicity on genetic material were also determined using the RAPD (randomly amplified polymorphic DNA) technique. While boron led to DNA damage in wheat seedlings, estrone significantly mitigated this damage. Element analysis demonstrated that estrone did not prevent boron uptake by roots, whereas it did stimulate the transportation of lead from roots to leaves. Taken together, our data demonstrate a versatile manner for the first time that estrone-induced boron tolerance is associated with many biochemical and molecular mechanisms, including the antioxidant system, ROS detoxification, modulation of uptake and transportation of boron and protection of genetic material.