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Pennyroyal (Mentha pulegium L.) from the Lamiaceae family is a medicinal plant which has great antioxidant properties. Environmental stresses such as drought can result in changes in the activity of antioxidant enzymes and the content of some biochemical factors in plants. In this investigation, the effects of drought stress on the activity of supe-roxide dismutase, ascorbate peroxidase, catalase, peroxidase, malondialdehyde and soluble sugars content in pennyroyal shoots and roots were evaluated. To create the water deficit, 24-day seedlings of pennyroyal were placed in 1/2 strength Hoagland solution, containing PEG 6000 (0 and 5% (w/v)) for 24 hours. The results showed that drought stress incr-eased catalase activity and lipid peroxidation and decreased superoxide dismutase and peroxidase activity of the shoots. On the other hand, the activity of catalase and peroxidase increased in the roots. Ascorbate peroxidase activity showed no significant difference in the shoots and the roots. Moreover, drought stress significantly increased the amount of so-luble sugars of glucose, galactose, xylose and rhamnosus in the shoots. Therefore, the increased activity in antioxidant enzymes as well as the amount of soluble sugars under drought stress might be a sign of tolerance of M. pulegium under low levels of drought.

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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.