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    Arbuscular Mycorrhizal Fungi and K-Humate Combined as Biostimulants: Changes in Antioxidant Defense System and Radical Scavenging Capacity inElaeagnus angustifolia
    (Springer International Publishing Ag, 2020) Torun, Hulya; Toprak, Bulent
    Arbuscular mycorrhizal fungi (AMF) and potassium humate (KH) are separately known as significant biostimulants, but their combined effect on plants remains elusive. This study investigated the single and combined roles of AMF and KH on the antioxidant defense system in Russian olive (Elaeagnus angustifoliaL.) leaves. Soil below the seeds was inoculated with indigenous AMF spores (Funneliformis,Claroideoglomus; 500 spores per seed). The KH (1.5 g/ per 1 kg of seed) was applied during sowing. Growth, leaf-water ratio, chlorophyll fluorescence, lipid peroxidation, H(2)O(2)content, antioxidant enzymes, and antioxidant capacity were analyzed in treated and untreated plants. Combined AMF and KH applications had a greater recovery effect on vegetative organ growth than separate treatments. With combined treatment, plants maintained leaf water status and chlorophyll fluorescence, while peroxidation of lipid membranes and H(2)O(2)content was reduced. Moreover, increases in superoxide dismutase and glutathione reductase activity prevented cellular damage from reactive oxygen species. Total phenolic content and antioxidant capacity values were remarkably higher in plants grown under the combined treatment. As a result, compared with their separate applications, a combination of AMF and KH enhanced the antioxidant defense system by increasing antioxidant enzymes and antioxidant capacity and, thus, could be used to enhance plant growth.
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    Editorial: Combined abiotic interactions in woody plants
    (Frontiers Media Sa, 2024) Torun, Hulya; Cocozza, Claudia; Petrik, Peter; Stojnic, Srdjan
    [No abstract available]
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    Melatonin application enhances salt stress-induced decreases in minerals, betalains, and phenolic acids in beet (Beta vulgaris L.) cultivars
    (Wiley, 2024) Colak, Nesrin; Slatnar, Ana; Medic, Aljaz; Torun, Hulya; Kurt-Celebi, Aynur; Draeger, Gerald; Djahandideh, Jasmin
    Melatonin is a potentially active signaling molecule and plays a crucial role in regulating the growth and development of plants under stress conditions, alleviating oxidative damage, enhancing antioxidant defence mechanisms and regulating ion homeostasis. This study examined the effects of exogenous melatonin application on leaf biomass, ion concentrations, betalains, phenolic acid and endogenous melatonin contents comparing red beet (Beta vulgaris L. 'Ruby Queen' and 'Scarlet Supreme') and white beet ('Rodeo' and 'Ansa') cultivars under increasing salinity levels of 50, 150, and 250 mM NaCl. Exogenous melatonin increased salinity-induced reductions in fresh and dry weights and osmotic potential in leaves. Na+ concentrations rose significantly with increasing salinity, but cultivar-specific decreases were observed in K+ and Ca2+ concentrations. Additionally, melatonin application improved betalain, betanin and neobetanin contents induced by salt stress. Furthermore, melatonin application caused salt stress and cultivar-specific changes in phenolic acid contents e.g., ferulic acid, sinapic acid, or m-coumaric acid, in soluble free, ester- and glycoside-conjugated and cell wall-bound forms. In addition, antioxidant enzyme activities and compound contents increased significantly in the beets and were subsequently lowered in a cultivar-specific manner by salt stress + melatonin treatment. The current findings indicate that exogenous melatonin improved plant stress tolerance suppressing reactive oxygen species levels, increasing the antioxidant enzyme activities and compound contents and reducing the levels of Na+, maintaining an ionic homeostasis in the selected red and white sugar beet cultivars. It appears that melatonin application may help improve cultivar-specific salt tolerance by enhancing ion homeostasis and betalain and phenolic acid production levels in beets.
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    Salicylic acid alleviates the effects of cadmium and drought stress by regulating water status, ions, and antioxidant defense in Pterocarya fraxinifolia
    (Frontiers Media Sa, 2024) Torun, Hulya; Cetin, Bilal; Stojnic, Srdjan; Petrik, Peter
    Introduction: Pterocarya fraxinifolia (Poiret) Spach (Caucasian wingnut, Juglandaceae) is a relict tree species, and little is known about its tolerance to abiotic stress factors, including drought stress and heavy metal toxicity. In addition, salicylic acid (SA) has been shown to have a pivotal role in plant responses to biotic and abiotic stresses. Methods: The current study is focused on evaluating the impact of foliar application of SA in mediating Caucasian wingnut physiological and biochemical responses, including growth, relative water content (RWC), osmotic potential (Psi s), quantum yield (Fv/Fm), electrolyte leakage, lipid peroxidation, hydrogen peroxide, and antioxidant enzymes, to cadmium (Cd; 100 mu M) and drought stress, as well as their interaction. Moreover, the antioxidant activity (e.g., ascorbate peroxidase, catalase, glutathione reductase, peroxidase, and superoxide dismutase activities) of the stressed trees was investigated. The study was conducted on 6-month-old seedlings under controlled environmental conditions in a greenhouse for 3 weeks. Results and discussion: Leaf length, RWC, Psi s, and Fv/Fm were decreased under all treatments, although the effect of drought stress was the most pronounced. An efficient antioxidant defense mechanism was detected in Caucasian wingnut. Moreover, SA-treated Caucasian wingnut plants had lower lipid peroxidation, as one of the indicators of oxidative stress, when compared to non-SA-treated groups, suggesting the tolerance of this plant to Cd stress, drought stress, and their combination. Cadmium and drought stress also changed the ion concentrations in Caucasian wingnut, causing excessive accumulation of Cd in leaves. These results highlight the beneficial function of SA in reducing the negative effects of Cd and drought stress on Caucasian wingnut plants.
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    Somatic drought stress memory affects leaf morpho-physiological traits of plants via epigenetic mechanisms and phytohormonal signalling
    (Elsevier, 2025) Alongi, Franklin; Petek-Petrik, Anja; Mukarram, Mohammad; Torun, Hulya; Schuldt, Bernhard; Petrik, Peter
    Drought stress memory in plants is an adaptive mechanism that enhances resilience to future water stress through physiological and molecular modifications triggered by previous drought events. This review explores somatic drought stress memory within a plant's lifespan, with a specific focus on leaf and stomatal morphology, minimum leaf conductance, photosynthetic efficiency, water-use efficiency, antioxidant capacity, and leaf senescence. We examine how epigenetic mechanisms-such as DNA methylation, histone modifications, and non-coding RNAs-regulate gene expression in coordination with hormonal signalling pathways. Phytohormones, including abscisic acid, jasmonic acid, ethylene, salicylic acid, auxins and cytokinins, are central to these processes, influencing key morphological and physiological adaptations, such as stomatal regulation, cuticle thickness, water retention, and improved water-use efficiency. The review synthesizes current knowledge on the molecular and hormonal networks underlying these adaptations and their impact on leaf architecture and metabolism. Despite advancements, critical gaps remain in identifying the specific genes and pathways involved, understanding the longevity of epigenetic marks, and elucidating the intricate cross-talk between phytohormones during drought stress memory. This review emphasizes the need for integrated-omics approaches to map epigenetic modifications and uncover their roles in developing drought-resistant plants through targeted stress priming strategies.
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    Timing-dependent effects of salicylic acid treatment on phytohormonal changes, ROS regulation, and antioxidant defense in salinized barley (Hordeum vulgare L.)
    (Nature Portfolio, 2020) Torun, Hulya; Novak, Ondrej; Mikulik, Jaromir; Pencik, Ales; Strnad, Miroslav; Ayaz, Faik Ahmet
    Cross-talk between exogenous salicylic acid (SA) and endogenous phytohormone pathways affects the antioxidant defense system and its response to salt stress. The study presented here investigated the effects of SA treatment before and during salt stress on the levels of endogenous plant growth regulators in three barley cultivars with different salinity tolerances: Hordeum vulgare L. cvs. Akhisar (sensitive), Erginel (moderate), and Kalayc (tolerant). The cultivars' relative leaf water contents, growth parameters, proline contents, chlorophyll a/b ratios, and lipid peroxidation levels were measured, along with the activities of enzymes involved in detoxifying reactive oxygen species (ROS) including superoxide-dismutase, peroxidase, catalase, ascorbate-peroxidase, and glutathione-reductase. In addition, levels of several endogenous phytohormones (indole-3-acetic-acid, cytokinins, abscisic acid, jasmonic acid, and ethylene) were measured. Barley is known to be more salt tolerant than related plant species. Accordingly, none of the studied cultivars exhibited changes in membrane lipid peroxidation under salt stress. However, they responded differently to salt-stress with respect to their accumulation of phytohormones and antioxidant enzyme activity. The strongest and weakest increases in ABA and proline accumulation were observed in Kalayc and Akhisar, respectively, suggesting that salt-stress was more effectively managed in Kalayc. The effects of exogenous SA treatment depended on both the timing of the treatment and the cultivar to which it was applied. In general, however, where SA helped mitigate salt stress, it appeared to do so by increasing ROS scavenging capacity and antioxidant enzyme activity. SA treatment also induced changes in phytohormone levels, presumably as a consequence of SA-phytohormone salt-stress cross-talk.