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Tea was planted in Lahijan by Kashefalsataneh in 1930. The main concern about important commercial plants such as tea is the formation of ice crystals in low temperatures. This can damage the live cells leading to lowering the quality of the plant and eventually its death. Formation of reactive oxygen species (ROS) and oxidative stress is the result of various environmental stresses leading to freezing. Investigating the variations in any of these factors could help to understand the mechanism of freeze resistance in ever-green plants. The aim of the present research was to investigate lipid peroxidation, the presence of antifreeze protein and variations in the activity of some antioxidant enzymes, including superoxide dismutase (SOD), ascorbate peroxidize (APX) and catalyse (CAT) in tea leaves subjected to 20, 0, -2, -5 and -8°C in tea leaves from the north of Iran. The results showed formation of an antifreeze protein with MW of about 20 KD in response to cold stress. It was also found that the activity of SOD, APX and CAT increased in tea leaves due to cold stress. The activity of SOD increased down to -8°C. APX and CAT increased their activity down to -5°C. On the other hand, the lipid per oxidation factor, MDA, was also elevated in response to the cold stress.

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Heavy metals reduce the plant growth and adversely affect plant performance potential. Heavy metals also induce the formation of reactive oxygen species leading to cell damage. Plants deal with heavy metal stress by activating enzymatic and non-enzymatic antioxidant systems such as Superoxide Dismutase which converts superoxide anion to hydrogen peroxide. Then Peroxidase and Catalase convert hydrogen peroxide to water. Another method employed by pl-ants to deal with heavy metals is mycorrhizal symbiosis. In this study, mycorrhizal and non-mycorrhizal barley seedlings (Hordeum vulgar), var. Rayhan, grown in a greenhouse were treated with four concentrations of nickel (0,100,200 and 400 µg/g). Results showed greater antioxidant activity in mycorrhizal plants compared with non-mycorrhizal plants.  Also, it was determined that the accumulation of nickel in roots of mycorrhizal plants was greater compared with non-mycorrhizal plants.

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In recent years, the involvement of nitric oxide (NO) in numerous physiological processes, particularly the mitigation of stress-induced negative effects on plants, has been clarified. Under salinity conditions, plants are subjected to a secondary oxidative stress.  The present work was designed to examine the exogenous application of nitric oxide (NO), in the form of its donor sodium nitroprusside (SNP), in mitigating the deleterious effects of salinity on Zygoph-yllum fabago L. plants. SNP (200 µM) was applied to plants growing medium under saline (200 and 400 mM NaCl) and non-saline conditions. Growth, oxidative stress markers [cell membrane stability index (MSI) and H₂O₂ conc-entration], antioxidant enzymes activities [peroxidase (POX, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6)], as well as the contents of some antioxidant compounds (flavonoids and carotenoids) were determined. Salinity lowered the shoot and root dry weights, while it enhanced peroxidase and catalase activities. High salinity increased H₂O₂; however, it de-creased the carotenoids content of leaves. Exogenous NO enhanced the growth, MSI, flavonoids and carotenoids co-ntents of salinized plants. In salinity plus SNP treated plants, H₂O₂ concentration and the activities of the examined en-zymes were reduced. Data suggest that a cooperative process is performed by the antioxidant systems in Syrian bean ca-per in order to cope with salinity. Also, the application of exogenous NO was found to be useful in the mitigation of salinity-induced oxidative stress in plants.

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Plant peroxidase (EC: 1.11.1.7) a heme-containing protein which is widely used in plants, microorganisms and animals. This two - substrate enzyme, catalyze the hydrogen peroxide into water with   oxidation of many organic and inorganic substrates that all of them can be used to measure enzyme activity. Although it’s specific substrate is hydrogen peroxide. Calcium and at least four disulfide bonds in the protein structure lead the formation and strength of three-dimensional structure of the molecule. Plant peroxidase has several roles including, involvement in lignin biosynthesis, auxin metabolism, cell growth, cell wall cross linking and respond to environmental stress. So peroxidase, considered as a good point to pursue the cell deal with stress factors such as oxidative stress. These days according to produce the pure samples of this molecule, peroxidase also used in ligand-protein studies in pharmaceutical research. So in this brief overview, in addition to introducing plant peroxidase we have had a brief look to measure the enzyme activity, the number of isoenzymes in a cell and the ensuing conformational changes of peroxidase.

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Antioxidant enzymes play an important role in plant defense against pathogenic agents. Following the identification of the pathogen, plants produce active oxygen species (ROS) as one of their first defense responses. To maintain the balance of ROS levels and prevent their harmful effects, plants produce antioxidant peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) enzymes. In the present study, the resistance of bean plants cultivars, namely Sadri, Paak, Darakhshan and Dorsa, to Xanthomonas axonopodis pv. phaseoli (Xap) were studied in greenhouse conditions. The catalase, peroxidase and ascorbate peroxidase enzyme activities were studied in healthy and Xap-infected bean cultivars Sadri and Derakhshan at 0, 24, 48, 72 hours and 20 days post inoculation by a completely randomized design with 5 treatments and 4 replications. The result showed that disease symptoms appeared in all tested cultivars. Derakhshan and Sadri cultivars, with 58.33 and 80.56 percentages of infected plants 20 days after inoculation, showed the least and highest infection rates, respectively. The highest catalase and peroxidase activities were recorded 24 and 48h post inoculation. These records reduced 48 and 72 hours post inoculation, respectively. The activities of these two enzymes in the susceptible cultivar were less than those in the semi-resistant one. The chlorophyll a and chlorophyll b contents of Xap-infected plants reduced significantly. The total chlorophyll content of uninfected Sadri and Darakhshan cultivars were 2.93 and 3.23 µg/g, respectively, which reduced to 1.96 and 2.14 µg/g of leaf tissue in infected plants, respectively. Based on these results, it is suggested that the Derakhshan cultivar should be planted in disease-susceptible regions as the semi-resistant cultivar.
 
 

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The Moldavian dragonhead (Dracocephalum moldavica L., Lamiaceae) is an annual medicinal plant with beneficial nutritional sources that plays important roles in human and animal feed. Nanoparticles and cold atmospheric plasma increase biochemical compounds in plants. In this study, the effects of copper nanoparticles and cold atmospheric plasma on biochemical indices of the medicinal plant Dracocephalum moldavica were investigated. Moldavian dragonhead plants were subjected to four doses of copper nanoparticles (0, 25, 50 and 75 mgl^-1) and cold atmospheric plasma at three durations (zero, 20 and 30 s). The results showed that cold atmospheric plasma significantly increases the essential oil percentage, while it decreases the amount of flavonoid content and activity of catalase and peroxidase enzymes. Cold atmospheric plasma (20 s) showed significant positive impact on essential oil content, while different time duration (20 and 30 s) did not show a significant impact on other traits. Lower doses of copper nanoparticles (25 and 50 mgl^-1) showed positive impacts on measured traits, while 75 mgl^-1 dose negatively affected the measured traits and functioned as a heavy metal. The cold atmospheric plasma and copper nanoparticles interactions indicated that cold atmospheric plasma had an incremental effect on the improvement of measured traits and increased the effect of copper nanoparticles. In conclusion, the results showed that copper nanoparticles with 25 mgl^-1 dose along with cold atmospheric plasma with 20 s duration had significant positive effects on the improvement of biochemical indices of Dracocephalum moldavica.
 
 

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Selenium, a non-essential element for plants, is essential for animals as well as human beings. Although the role of selenium in plants is yet to be properly understood, previous researches have shown that this element can affect plant growth and metabolism. In this study, the effect of foliar application of selenium nanoparticles (0, 5, 10, and 20 mg/L) and sodium selenate (0, 5, 10, and 20 mg/L) on the physiological and biochemical responses of bell pepper (Capsicum anumm L.) was investigated. The potential changes in various growth and biochemical indices were evaluated in response to the treatments. According to the results, selenium treatments at concentrations of 10 and 20 mg/L reduced the biomass accumulation in both roots and shoots. These treatments also increased the content of hydrogen peroxide and malondialdehyde. The foliar application of selenium led to the increase of the concentrations of soluble phenols, proline and thiols. The activity of antioxidant enzymes including catalase, peroxidase, ascorbate peroxidase, and polyphenol oxidase were increased in response to the selenium treatments. The protease activity displayed a similar upward trend following the selenium treatments.

 

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Fennel is a medicinal plant; all of its parts were being used by humans in different ways. This plant is relatively sensitive to salinity. A factorial experiment as a randomized complete block design with three replications at the greenhouse level was executed to investigate the effect of vermicompost on the increase of salinity tolerance in four fennel populations (Mashhad, Urmia, Shiraz, and Bushehr) in the vegetative stage of the plant, emphasizing the evaluation of some osmotic and antioxidant protection indicators. Experimental treatments were designed with four levels of salinity (0, 40, 80, and 120 mM of NaCl) and two levels of vermicompost (0 and 5% v/v). After harvesting, the roots were separated from the stem to analyze the biochemical variables. Salt stress caused a decrease in the total soluble sugar and starch content in the shoot and an increase of those in the root of the studied populations. In addition, under stress conditions, the proline content of shoot and root, total free amino acid, total phenol, and activity of guaiacol peroxidase and catalase were increased in fennel populations, while total soluble protein and anthocyanin content were decreased. Vermicompost treatment increased the content of soluble carbohydrates, soluble protein, free amino acids, proline, total phenol, and anthocyanin, and decreased the activity of guaiacol peroxidase in the shoot, as well as the starch content in the roots of fennel populations under non-stressed and stressed conditions. Despite observing the complexity in the changes of the analyzed indicators which were dependent on the type of population and the dose of stress, our results showed that the application of vermicompost with a concentration of 5% can improve the osmotic and antioxidant protection in the studied populations of fennel under salinity stress.