Silicon (Si) can protect some plants from biotic and abiotic stresses. In this research, effects of three exogenous Si levels (0, 0.85 and 1.7 mM) on growth, lipid peroxidation, LIPOXYGENASE activity, proline content, H2O2 accumulation, and activity of non-enzymatic and enzymatic antioxidants (catalase and ascorbate peroxidase) under powdery mildew disease stress by Sphaerotheca fuliginea on pumpkin (Cucurbita pepo, var. styriaca), under hydroponic conditions, were investigated. The results revealed that effect of Si in reduction of powdery mildew was significant (P£0.05) and application of 1.7 mM of this element decreased the severity of disease symptoms up to 35%. Increasing the Si concentration in the nutrients solution elevated the amount of this element in roots and shoots of pumpkin plants. The concentration of H2O2, lipid peroxidation and LIPOXYGENASE activity were increased by disease stress. But these parameters were decreased with application of Si. The activity of enzymatic and non-enzymatic antioxidants was significantly enhanced (P£0.05) by the application of Si. Based on the present work, it can be concluded that concentration level of 1.7 mM Si was more effective than the other two treatments in alleviating disease stress, which could be related to the effect of this element on prevention of membrane lipid-oxidation.

Bioactive food components (such as phenolic compounds, carotenoids, anthocyanins, tochopherols, ascorbic acid, flavonoids, minerals, enzymes and pectin) are active ingredients in food or dietary supplements, which proven to have an important role in health, and are safe for human consumption. These compounds exert their antioxidant effects by different mechanisms such as single electron transfer or hydrogen atom transfer, and their efficiencies can be evaluated by several methods such as ferric reducing ability of plasma, oxygen radical absorbance capacity assay, total radical trapping antioxidant parameter, total oxidant scavenging capacity, conjugated dienes, LIPOXYGENASE activity inhibition assay, chemiluminescence, deoxyribose, tocopheroxyl radical attenuating ability, and nitric oxide radicals trapping. In this review, these mechanisms and methods will be discussed in details.

In this research, the effects of electromagnetic fields of various strengths (0, 1 and 2mT) have been investigated on antioxidant enzymes activity in Valerian (Valeriana officinal is L.). The dry and wet (soaked for 30 min) Valerian seeds were exposed to electromagnetic fields 30 min per day for 3 days. Each treatment and control groups had 3 replicates and 10 seeds were employed for each replicate. Results showed that electromagnetic field treatment increased significantly root length, fresh and dry weight, ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, polyphenol oxidase and LIPOXYGENASE activity compared to control for most treatment groups especially in the groups of dry treated seeds. These results showed that electromagnetic fields probably enhanced oxidative stress and treated Valerian seeds probably increased antioxidant enzymes activity to inhibit overproduction of free radicals against electromagnetic fields tension.

The transcript levels of six defense genes including pathogenesis-related gene 1 (PR-1), pathogenesis-related gene 2 (PR-2), pathogenesis-related gene 5 (PR-5), LIPOXYGENASE (LOX), phenylalanine ammonia-lyase (PAL) and catalase (CAT) were investigated in tomato plants inoculated with Xanthomonas axonopodis pv. phaseoli as a non-host pathogen and X. euvesicatoria as a host pathogen. Activation of all the genes was confirmed in both host and non-host treatments. Additionally, the results showed stronger expression of majority of the genes (PR-1, PR-2, LOX, PAL and CAT) in non-host treatment compared to host treatment at least at early hours after inoculation. These data suggest that faster and more expression of PR-1, PR-2, LOX, PAL and CAT might have a role in non-host resistance of tomato against X. axonopodis pv. phaseoli.

In order to understand of the molecular mechanisms of drought tolerance in sunflower, proteomic pattern of roots in two drought sensitive and drought-tolerant lines were evaluated under limited and favorable water conditions. After 2DE and comparison of relative abundance of protein spots using t test, 12 of 417 protein spots in sensitive and 17 of 467 in tolerant line were affected by drought stress significantly. Following nano-LC MS/MS the protein spots were identified using Mascot search engine in NCBI protein database considering more than 10 % sequence coverage and score of above 80. Cytoplasmic and nuclear proteins were the most proteins which were affected by water deficiency. Three protein spots i. e. Enolase, Glyceraldehyde 3-phosphate dehydrogenase and Chalcone synthase were expressed differentially in these lines. Reduction of Enolase as a sign of metabolic impairment could be resulted in downstream process under drought stress. Increased expression of Glyceraldehyde 3-phosphate dehydrogenase and Chalcone synthase could have a role in detoxification/removal of oxidative destruction and antioxidant capability of the tolerant line. Increased level of heat shock protein, dihydroflavonol reductase, Seed linoleate 9S-LIPOXYGENASE, Ubiquitin carboxyl-terminal hydrolase and G protein indicated crucial role of defensive, protective and transductive process in reduction of drought injuries.

Mitochondrial dysfunction is one of the main causative factors in a wide variety of complications such as neurodegenerative disorders, ischemia/reperfusion, aging process, and septic shock. Decrease in respiratory complex activity, increase in free radical production, increase in mitochondrial synthase activity, increase in nitric oxide production, and impair in electron transport system and/ormitochondrial permeability are considered as the main factors responsible for mitochondrial dysfunction. Melatonin, the pinealgland hormone, is selectively taken up by mitochondria and acts as a powerful antioxidant, regulating the mitochondrial bioenergeticfunction. Melatonin increases the permeability of membranes and is the stimulator of antioxidant enzymes including superoxidedismutase, glutathione peroxidase, glutathione reductase, and catalase. It also acts as an inhibitor of LIPOXYGENASE. Melatonin cancause resistance to oxidation damage by fixing the microsomal membranes. Melatonin has been shown to retard aging and inhibitneurodegenerative disorders, ischemia/reperfusion, septic shock, diabetes, cancer, and other complications related to oxidative stress.The purpose of the current study, other than introducing melatonin, was to present the recent findings on clinical effects in diseasesrelated to mitochondrial dysfunction including diabetes, cancer, gastrointestinal diseases, and diseases related to brain function.

In the present research, we studied the effects of salicylic acid (SA) in canola plants undergoing oxidative stress caused by nickel (Ni). 21-day-old canola plants were exposed to variable concentrations of NiCl2.6H2O (0, 0.5, 1 mM) and SA (0, 0.2 mM).Ni was more accumulated in roots than in shoots. Interestingly, root-to-shoot translocation of Ni decreased by SA. In the absence of SA, excess Ni decreased dry weight of roots and shoots and reduced chlorophyll content in leaves, while SA moderated these effects. In Ni-treated plants, level of LIPOXYGENASE activity and the contents of malondialdehyde and H2O2 increased, as well as changes in the activities of the antioxidant enzymes, catalase, guaiacol peroxidase and superoxide dismutase, in leaves indicated that Ni caused an oxidative stress in canola plants. Addition of SA together with Ni ions, markedly modified LOX activity and reduced MDA and H2O2 content. Also, SA significantly increased the activities of the antioxidant enzymes in leaves of Ni-stressed plants. Consequently, salicylic acid by sequestration of Ni in roots and with increase in the activities of antioxidant enzymes reduces Ni induced oxidative damage in a certain extent.

In this work, the effects of two commercial bio-fungicides-Biosubtyl (Bacillus subtilis) and Biophosphorus (Pseudomonas sp. )-on disease incidence and plant cell defense mechanisms were investigated. Changes in disease severity, plant defense enzyme activity, phenolic compounds content and representative defense-related genes expression were measured in cucumber plantlets infected with Phytophthora melonis at 24, 48, 72 and 96 hours post inoculation (hpi). The incidence rate of disease decreased in treated plants with both bio-fertilizers. The highest reduced rate of disease (60%) was noted for Biosubtyl application compared to control treatment. Biochemical analyses showed that both bio-fertilizers are able to increase total protein and phenolic compounds in infected cucumber plants. Highest activities of Peroxidase )PO) and β-1, 3-glucanase enzymes were measured for bio-phosphorus application at 72 hpi while maximum expression of Polyphenol oxidase (PPO) was observed at 96 hpi for this application. Transcriptional activities of, LIPOXYGENASE (Lox) showed an optimum at 72hpi (p-value < 0. 01, 9. 5 fold), while genes coding for cucumber pathogen-induced 4 (Cupi4), Phenylalanine ammonia lyase (PAL) and Galactinol synthase (Gal) presented high expression levels at 48 hpi in infected cucumber plants treated with Biophosporus. These results suggest that both bio-fertilizers could improve enhanced disease resistance in infected cucumber by inducing basal resistance mechanisms and can be used as a natural alternative to conventional fungicides for sustainable disease control.

In this study, the role of riboflavin (vitamin B2) as a defense activator in rice plant against Rhizoctonia diseases was investigated. Following application of riboflavin, rice plants developed systemic resistance to the pathogen and riboflavin did not have any direct effect on the growth pathogens and did not cause phytotoxicity on plants. The necessity of the time interval between riboflavin application and inoculation of pathogen for reduction of disease progress clearly indicates that riboflavin protects rice against R. solani by inducing plant defense responses and induction of resistance. This case was further confirmed by investigating the expression of defense genes, including cationic rice perroxidase (PO-C1), phenylalaninr ammonia-lyase (PAL), and LIPOXYGENASE (LOX). Results revealed elevated levels of LOX and PO-C1 expression in riboflavin-treated plants especially after inoculation with the pathogen. Induction of resistance in plant even after 20 days post-treatment with riboflavin reveales that the vitamin is effective for induction of more durable resistance compared to other activators of plant defense system. Our findings demonstrate that using riboflavin as a plant defense activator is a new, simple, and environmentally safe strategy that could be used to control Rhizoctonia sheath diseases of rice.

The gene 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and TcGLIP multifunctional genes are two key genes involved in pyrethrins biosynthetic pathway, which retain insecticidal properties. DXS gene in the MEP pathway produces 1-deoxy-d-xylulose 5-phosphate using pyruvate and glyceraldehyde-3-phosphate dehydrogenase. TcGLIP gene is involved at the last steps of pyrethrins biosynthesis pathway and integrates chrysanthemyl-CoA and pyrethrolone, which are produced in the MEP pathway and LIPOXYGENASE pathways, respectively to yield pyrethrin I. Based on the significances of pyrethrins, further identification and studies are needed on these metabolites. The aim of this study was to isolate DXS gene in pyrethrum (Chrysanthemum cinerariaefolium Vis. ) from the Asteraceae, as well as expression analysis of these two genes under methyl-jasmonate treatment. In the present work, the nucleotide sequences of 1-deoxy-D-xylulose 5-phosphate synthase gene of different plant species were obtained from NCBI database and subsequently aligned with ClustalW online software. Specific primers were designed from the conserved regions of aligned sequences. The polymerase chain reaction product with 715bp length showed that the specific primers had high efficiency to isolate DXS. In addition, gene expression analysis under methyl-jasmonate treatment showed that both DXS and TcGLIP were up-regulated in response to methyl jasmonate elicitor. Our data showed that methyl jasmonate treatment in seedling stage could be used as a suitable elicitor to increase pyrethrin production.