قادر حبیبی

In the current study, the toxicity of zinc oxide nanoparticles (ZnONPs) and zinc sulfate (ZnSO4) in Hypericum perforatum L. pre-treated with salicylic acid and nitric oxide (sodium nitroprusside) at a concentration of 0.1 mM was investigated in a completely randomized design with three replicates as pot culture in perlite. After 21 days of treatment, the plants were harvested. The results of the variance analysis of the data in the laboratory showed that the application of 1000 mgL-1 of zinc oxide or zinc sulfate nanoparticles caused more toxicity. However, the greatest effect is related to the pretreatment of salicylic acid and nitric oxide (sodium nitroprusside), which successfully reduced the value of the oxidative stress index (malondialdehyde) and as a result, the adverse effect of zinc on the seed germination of gerbera. The combination of salicylic acid and nitric oxide increased the amount of proline in the treatment of zinc oxide nanoparticles and phenol antioxidants had a significant increase under the effect of zinc oxide nanoparticles and zinc sulfate, which was associated with an increase in the activity of the phenylalanine ammoni alyase enzyme. The amount of zinc in the roots also increased with the combination of salicylic acid and nitric oxide under the stress of zinc oxide nanoparticles. In this research, it was tried to minimize the negative effect of zinc oxide nanoparticles and zinc sulfate on plant products by designing new methods.

In this study, seasonal and diurnal changes in photosynthesis and phenolic metabolism in evergreen jasmin (Jasminum fruticans L.) were examined over a 12-month period. We found the differences in pigment and phenolic contents between the values determined during the autumn and winter months and the values determined during the spring and summer months. During the autumn and winter months, the low seasonality of Chla was accompanied by increases in both carotenoids and phenol levels which play a major role in photoprotection processes. While the maximal quantum efficiency of PSII (Fv/Fm) showed diurnal changes during the winter months, such diurnal changes were not observed for the other seasons. These diurnal changes reflected dynamic photoinhibition, as an adaptation mechanism, which may actually protect the leaves against photodamage under cold conditions. During the winter months, increased O–J phase (from the OJIP chlorophyll fluorescence curve) and decreased I–P phase in parallel with the reduction of Fv/Fm, revealed that the cold stress influenced both the donor and acceptor sides of PSII. Interestingly, we found the relationship between diurnal changes of Fv/Fm and those of hydrogen peroxide (H2O2) levels and catalase (CAT) activity during the winter months. Diurnal changes in CAT activity represented the differences between the values determined in warm and cold seasons. Compared with the diurnal changes during the spring and summer months, the maximum activity of CAT was observed at 15:00 h during the winter months, which indicated that CAT may play an effective role in protection of photosystems under a high photosynthetically active radiation (PAR) during cold days.

Salinity is one of the most important abiotic stresses that affects seed yield and crop production. Salinity causes adverse morphological, physiological and biochemical effects on wheat seedlings. In this research, the effects of seed priming (1 mM proline) on the response of wheat plants (Triticum aestivum L.) to salinity stress in acclimatized and non-acclimatized conditions were investigated. Wheat seeds were subjected to acclimatization and seed priming with proline (1 mM) for 12 hours. Then, the seeds were planted in pots containing saline soil (EC=26.5 dS/m) and plant growth and physiological parameters were investigated. The results showed that in non-stressed conditions, seed yield increased with proline treatment. Pretreatment of seeds with proline under salinity stress preserved their photosynthetic performance compared to acclimatization. The results of examining the characteristics of shoot dry weight along with the measurement of malondialdehyde showed that acclimatization with low salt concentration cannot reduce the inhibitory effect of high salinity (EC=26.5 dS/m). Therefore, more research is needed to optimize the acclimatization protocol, seed osmopriming factors and environmental conditions to increase plant tolerance to salinity stress

In this study, the effect of salicylic acid and sodium nitroprusside on the toxicity of zinc oxide nanoparticles (ZnONPs) and zinc sulfate (ZnSO4) in Phlomis tuberosa was investigated. The purpose of this research was to investigate new methods of increasing the tolerance threshold of Phlomis plants under the influence of zinc oxide and zinc sulfate nanoparticles toxicity. This experiment was conducted in the form of a completely randomized design with three replications in the form of pot cultivation in a perlite bed, and the plants were harvested after 21 days of treatment. The measured factors included total chlorophyll, carotenoid, total phenol, flavonoid, the activity of phenylalanine ammonia lyase, catalase, superoxide dismutase, and ascorbate peroxidase. The results of the analysis of the variance of the data in the laboratory showed that the application of 1000 mgL-1 of zinc oxide nanoparticles or zinc sulfate caused more toxicity. The interaction effect of salicylic acid and sodium nitroprusside pretreatments on zinc oxide nanoparticles in Phlomis seedlings was significant and salicylic acid pretreatment increased the amount of proline in the treatment of zinc oxide nanoparticles. Phenol antioxidants increased significantly under the effect of zinc oxide and zinc sulfate nanoparticles, which was associated with an increase in the activity of the phenylalanine ammonia lyase enzyme. Salicylic acid pretreatment showed the greatest effect in the Phlomis plant compared to the combination of salicylic acid and nitric oxide.

Seed osmopriming is an effective strategy to improve the germination process. Screening and estimating the optimal concentrations of different osmotic compounds is the first step in seed osmopriming. In this study, the effects of treatment with single osmotic compounds were initially evaluated at different concentrations, namely NaCl (0, 1, 2, 3, 4, 5, 10, 20, 30 g/l), ZnSO4 (0, 1, 5, 10, 20, 30 and 40 mM), proline (0, 1, 5, 10, 20, 30 and 40 mM), and trehalose (0, 1, 5, 10, 20, 30 and 40 mM) on wheat seeds. Then, the surface-response method was designed in the form of a Box-Benken design. Results showed a significant increase in wheat seed germination at concentrations of 3 and 10 g/l NaCl, 1 and 20 mM ZnSO4, 1 and 10 mM proline, and 0 and 1 mM trehalose. These concentrations were validated using the surface-response method and experiments. The values of coefficient of determination (R2 = 0.99) and adjusted R2 (R2adj = 0.99) showed that the obtained model is suitable for data analysis. One-way analysis of variance confirmed the quadratic model as the best model to determine the interaction of the studied variables (P<0.0001). The optimal values  were proposed as a combination of 3 g/l NaCl, 1 mM ZnSO4, and 1 mM proline. In another experiment, using the values predicted by the model, it was found that the surface-response method can be used in screening and germination optimization tests. The results of the follow up experiment using the values determined in the model revealed that the surface-response method can be considered in screening and optimization studies of seed germination.

In this study, we investigated the role of salicylic acid (SA) and hydrogen peroxide (H2O2) priming in ameliorating salinity stress on wheat (Triticum aestivum L. cv Mihan) grown under hydroponic culture. Seeds of wheat were primed in distilled water (control), as well as different solutions of salicylic acid (0.1, 0.5 and 1 mM) and/or H2O2 (1, 20 and 200 mM) for 24 h at 25°C. Seven-day-old seedlings were transferred to Hoagland nutrient solution. Experiments were undertaken in complete randomized block design using 4 independent replications. Salinity stress drastically affected the plants as indicated by decreased biomass of shoots (about 25%). However, H2O2 priming at 20 mM raised free radical scavenging activities of wheat leaf, as evaluated by decrease in malondialdehyde (MDA) levels. These results indicated that H2O2 priming could prevent negative effects of salinity stress on the biomass and photosystem performance. While SA priming could not ameliorate the negative effect of salt on wheat seedlings, the use of both SA and H2O2 as priming agents had the most significant alleviating effect against NaCl stress. This ameliorative effect was achieved through stimulation of catalase activity (about 37%) and non-enzymatic (phenols) antioxidants (about 45%) and lowering tissue MDA contents. These results further confirm that the use of both SA and H2O2 as priming agents participated in the protection of membranes against the destabilizing effect of salt stress. Additionally, the use of both SA and H2O2 as priming agents mitigated the negative effects of salinity on the photochemical efficiency of PSII.

Due to the drying trend of Urmia Lake, climate change and frequent occurrence of droughts in the region, verification of photosynthetic flexibility in the floral elements of Lake Urmia is important. In this work, the ability of Rosularia elymaitica and Zygophyllum fabago species to shift from C3 to Crassulacean acid metabolism (CAM) as well as survival and productivity of these plants were studied in both salty and dry soils of Lake Urmia. While salinity alone was not able to induce functional CAM expression in both species, we showed that drought alone induced low level of nocturnal acid accumulation in both species, which were similar to acid fluctuations in CAM-cycling pathway, as an initial stage of CAM. We indicated that Z. fabago species have a high tolerance to combined drought (30 days water dificit) and salt (7±0.42 dSm-1) stresses in salty and dry soils of the Lake Urmia, as compared to R. elymaitica plants. This higher tolerance was correlated with up-regulation of phosphoenolpyruvate-carboxylase (PEPC) activity and maintenance of higher photochemical functioning. As a result, this research introduces Z. fabago as an important climate-resilient crop, which can switch from C3 to CAM in salty and dry soils of the Lake Urmia.

 Background and Objectives :

Salinity is one of the detrimental environmental factors that limit the productivity of crop plants worldwide. Most of the crop plants are sensitive to salinity. Selenium (Se) has not been classified as a plant essential element, but its role as a beneficial element and its ability in amelioration of different environmental stresses has been reported in different plant species. The aim of this study was to investigate the effects of Se on sunflower plants under salt stress conditions.

  Materials and Methods:

 The experiment was conducted as factorial in a completely randomized design by three replications in a hydroponic system with a temperature regime of 25/18°C, photoperiod of 14 h, and relative humidity of 70% in a growth chamber. Seeds were germinated in petri-dishes and then uniform 3-day old seedlings were transferred to 50% Hoagland solution. One week after pretreatment, plants were transferred to 100% Hoagland solution and treated with selenium) sodium selenate; 0, 5, and 10 µM) and salinity (sodium chloride; 50 and 100 mM) for two weeks. Plant's shoots were harvested 15 days after treatments, and frozen in liquid nitrogen until assays.  

Results:

 The results indicated that salinity at both levels significantly increased the MDA as well as free phenol and decreased the flavonoids contents of plants. The anthocyanin, soluble sugars, and total protein contents and the activity of APX increased significantly in response to 50 mM of NaCl, while the proline, tannins, and lignin contents increased, but dry weight and height of shoot decreased significantly in response to 100 mM of NaCl. In non-saline condition, Se application at 5 µM decreased the flavonoids and lignin contents and increased the free phenols, shoot height, and POD activity significantly. Application of Se at 10 µM in non-saline conditions significantly increased the lignin and MDA contents and APX activity. In saline condition with 50 mM of NaCl, Se application at both two levels decreased the soluble sugars and APX activity, and at 10 µM decreased the lignin and increased the tannin contents significantly. In saline condition with 100 mM of NaCl, Se application at both two concentrations considerably decreased the proline, lignin, and tannin contents but increased the APX activity. Furthermore, a reduction in soluble sugars by application of 5 µM of Se was seen in plants that were in saline conditions with 100 mM of NaCl.  

Discussion:

 According to the results of this study, salinity induced oxidative stress in sunflower, especially at 100 mM that was obvious by elevated level of MDA. Even though the Se application in saline condition could induce the notable changes in the phenolic compounds and promoted the activity of APX, it could not inhibit the MDA formation and dry weight falling in plants. Selenium application in non-saline conditions also could not result to the considerable benefits in sunflower plants.

In this study, we compared the impact of high Cu concentrations on the photosynthetic apparatus and antioxidant capacity of the Phlomis tuberosa. Plants were grown in perlite culture for 5 weeks, and then treated with 0, 100, 200, 300 and 400 µM Cu for 21 days. Results indicated that Phlomis tuberosa plants showed tolerance to 100 and 200 µM Cu. This increased tolerance was achieved through enhancement in antioxidant system activity. However, exposure to high Cu (300 and 400 µM) showed the highest level of stress leading to higher hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels and lower inferred oxygen evolving complex activity (Fv/Fo) and calculated Performance Index (PIabs) values. Based on effective concentration (EC50 – substrate Cu concentration resulting in 50% biomass reduction) parameter, Cu toxicity thresholds for Phlomis tuberosa plants were determined at substrate Cu levels up to 300 µM. Interestingly, plants exposed to medium Cu levels for 21 days exhibited higher nitric oxide (NO) accumulation in the leaves, which was associated with enhanced levels of antioxidative enzyme activities, whilst maintaining photosynthesis.

We examined the combined effects of hydrogen peroxide (H2O2) and nitric oxide (NO) on the responses of oilseed rape(Brassica napus L.) plants to salt stress under acclimated and non-acclimated conditions. The results of the shoot and root dry weight traits together with the measurement of malondialdehyde (MDA) indicated that salt acclimation with a low concentration of NaCl (50 mM) could not alleviate the inhibitory effect of high salinity (200 mM NaCl). Under acclimated conditions, seed priming with H2O2 or NO resulted in effective protection against salt stress, however, maximum amelioration of salt stress was found by the combined treatments of H2O2 + NO. Interestingly, in the salt-exposed non-acclimated plants, only seed priming with H2O2 + NO was effective in improving salt tolerance. Pretreatment with H2O2 + NO tended to limit Na translocation into photosynthetic organs to prevent salt damages. Additionally, a large increase in salicylic acid contentwas correlated with phenylalanine ammonia lyase activation and flavonoid biosynthesis was observed when oilseed rape plants exposed to salinity in the presence of H2O2+NO. Interestingly, in this study, endogenous NO content of H2O2–primed plants exhibited a significant increase under non-saline conditions, indicating that H2O2 influences NO accumulation. In addition, oilseed rape plants primed with H2O2 + NO exhibited lower MDA and H2O2 content, contributing to the better induction of antioxidative enzyme activities. Higher levels of antioxidant enzyme activities maintained the integrity of cell membranes, resulting in better plant growth under salt stress. Taken together, our results revealed that oilseed rape plants pretreated with H2O2 + NO exhibited more effective tolerance to salt stress than plants that were pretreated with H2O2 or NO alone.

Several studies have been conducted focusing on antioxidant capacity of medicinal plants; however information is lacking on the daily rhythm of antioxidant capacity as well as photochemical reactions in medicinal plants under natural conditions. Thus, in this study, changes in phenolic acids, PSII functioning and antioxidant enzymes activities in response to low (1,100 m) and high (2,200 m) elevation sites in Marrubium vulgare L. were investigated. Plants were harvested and analyzed in a temporal manner; and for the latter analysis, leaf samples were frozen immediately in liquid N2 and stored in it until assay. High-altitude plants exhibited higher phenolics and carotenoids than that in low-altitude plants, which was associated with higher phenylalanine ammonia-lyase (PAL) activity. Results indicated that the absolute amounts of antioxidant enzymes activities were considerably greater in high-altitude plants than low-altitude plants. High-altitude plants showed the rapidly reversible inhibition of PSII reaction centers (dynamic photoinhibition) associated with an increase in non-photochemical rate constant (kN), which was important photoprotection mechanism under high-mountain conditions. Surprisingly, the activities of antioxidative enzymes, the accumulation of hydrogen peroxide (H2O2), & the free radical scavenging activities using DPPH radical-scavenging in the leaves of high-altitude plants showed diurnal rhythm during the course of day. Finally, we found that the ability of dynamic photoinhibition was an important photoprotection process during periods of high solar radiation in the high-altitude Marrubium vulgare plants.

In this study, the effects of drought on some physiological characteristics of winter and spring leaves of jasmin (Jasminum fruticans L.) were examined in plants grown in pots and treated with or without water stress for 25 days. Our results showed significant difference in pigment content and phenolic metabolism between winter and spring leaves of jasmine during spring season. In this study, winter leaves showed the higher Chlb, carotanoids, total phenol, flavonoids as well as phenylalanine ammonia lyase (PAL) activity, and relative water content (RWC) as compared to spring leaves, indicating winter leaves are sufficient in their capacity for non-photochemical energy dissipation via these mechanisms. However, water stress did not significantly affect these parameters. Drought significantly increased the amount of malondoialdehyde (MDA) and hydrogen peroxide (H2O2) following significant enhancement of peroxidase (POD) activity. However, in winter and spring leaves treated with water stress, decrease in the maximal quantum efficiency of PSII (Fv/Fm) was not statistically significant. In contrary, spring leaves exhibited a significant decrease in the performance index (PIabs) parameter under drought conditions. Notably, the kinetics of the OJIP chlorophyll fluorescence curve exhibited a quicker difference between winter and spring leaves of jasmine under well watered conditions. Thus, photosynthetic apparatus of winter leaves maintained a higher PIabs during spring season, and showed more tolerance to water stress by dissipating excess light energy by carotenoids; and by screening of photoradiation by phenolic compounds.

In this study, to evaluate the effect of foliar-applied iodate (5 and 50 mg/l KIO3) on the improvement of tolerance to salt stress (50 mM NaCl) in strawberry plants (Fragaria × ananassa Duch.), an experiment was under taken in complete randomized block design (RBD). The photosynthetic apparatus of strawberry was damaged at 50 mM NaCl, as indicated by a decrease in performance index (PIabs) coupled with lower values of photosynthetic electron transport chain components including the electron transport flux (φEo) and the inferred oxygen evolving complex activity (Fv/Fo) as well as higher levels of malondialdehyde (MDA). Plants treated with a low concentration of KIO3 (5 mg/l) showed an increase in the leaf dry weight, total protein and soluble sugars content with respect to no KIO3 supply under salinity stress. Additionally, low concentration of KIO3 raised free radical scavenging activities of strawberry leaf because of an enhancement of total phenolic content as well as CAT activity. In contrast, plants supplemented by 50 mg/l KIO3 exhibited an extreme stress for the photosynthetic parameters ofstrawberry, as demonstrated by the changes in the Fv/Fo as well as higher levels of MDA was similar to that observed in salt treatments. While KIO3 at 5 mg/l could increase photosystem performance index under salt-stress conditions in addition to the stimulation of antioxidant system, KIO3 at 50 mg/l could not ameliorate the negative effect of salt on strawberry and led to toxicity and caused damage to photochemical reactions, which is mainly overlooked by other authors.

High light (HL) can limit plant photosynthetic activity, growth and productivity. The HL effect was more pronounced in plants grown at low temperature. In order to determine the effects of chilling stress (4 0C) and light intensities (450 and 850 µmol m-2 s-1) on antioxidant defense system and  phenolic metabolism of Aloe vera L., an experiment was  conducted in a randomized complete block design with four replications in a research greenhouse. The results indicated that the Aloe vera has a stronger HL tolerance. Increased tolerance in HL-treated plants was related to screening of photoradiation by phenolic compounds (but not the mechanism of ROS scavenging). Although total phenolics and flavonoids concentration as well as phenylalanine ammonia-lyase (PAL) and catalase (CAT) activity responded positively to the chilling treatment, but cold stress considerably increased the rise in malondialdehyde (MDA) content (as a marker of lipid peroxidation), suggesting that Aloe vera is sensitive to chilling treatment. Additionally, chilling raised free radical scavenging activities of Aloe vera leaf gel using DPPH radical-scavenging because of an enhancement of total phenolic, and may be recommended for increasing leaf gel quality.

Since the photochemical mechanisms of iodine-mediated adaptation to salt stress is not yet clear, the present study was performed to address this issue. Strawberry (Fragaria × ananassa Duch.) plants were grown under controlled conditions, and soils of iodine treatment were fertilized with potassium iodate (KIO
3 (5 and 50 mg/kg soil) before filling the pots. Salt stress (50 mM) negatively affected protein synthesis and photochemical reactions of strawberry, as evaluated by a decrease in performance index (PI
absas well as higher levels of hydrogen peroxide (H2O2) and malondialdehyde, whereas application of KIO
3
(at both 5 and 50 mg/kg) alleviated the detrimental effect of sodium chloride (NaCl) stress. Plants treated with 50 mg/kg showed an increase in the soluble sugars content with respect to no KIO
3
supply under salinity stress. In salt-stressed plants, the OJIP chlorophyll fluorescence curve showed a quicker fluorescence decrease in the I-P phase. Notably, I-P phase in plants treated with KIO
3
was increased. These results indicated that KIO
3
application could protect the photosystem II from damage under salinity stress. Additionally, application of KIO
3
raised free radical scavenging activities of strawberry leaf because of an enhancement of catalase activity. These data provided the first evidence that the root-applied KIO
3
pretreatment alleviated salt stress in strawberry by decreasing reactive oxygen species production, resulting in better photochemical functioning under salt stress

Oxidative stress is commonly induced when plants are grown under drought stress conditions.To analyze how salicylic acid (SA) can partly alleviate drought-induced oxidative stress and negative impacts of drought on physiology and growth of Salvia nemorosa plants, we investigated the physiological responses of S. nemorosa to SA application under drought stress. The treatments were composed of Co (control, 100% field capacity), Dr (drought, 50% field capacity), SA (500 µM) and DSA (SA drought). Plant growth and relative water content (RWC) were negatively affected by drought stress; however, SA treatment significantly improved the growth rate and enhanced the drought tolerance of seedlings. This increased tolerance in SA-supplied plants was obtained by reduced damaging effect on performance index (PIabs) and maximal quantum yield of photosystem II (PSII) (Fv/Fm) through improvement of reaction centers (RC/CS) with associated changes in excitation energy trapping (TRo/CS) and electron transport (ET0/CS) per excited cross-section of leaf. Additionally, under drought condition, plants cultivated with SA exhibited better protection against oxidative damage because of higher catalase (CAT) and ascorbate peroxidase (APX) activities and lower levels of malondoialdehyde (MDA) and hydrogen peroxide (H2O2). The present study suggests that salicylic acid can play a protective role during drought stress by enhancing the photosynthetic capacity and the antioxidant defense system.

High light damages photosynthetic machinery, primarily photosystem II (PSII), and causes photoinhibition that can limit plant photosynthetic activity, growth and productivity. To address this issue, we investigated the basic photoprotection mechanisms including ROS scavenging activity and phenolic compounds production in wheat (Triticum aestivum L.), as a C3 plant, after treatment with low temperature (4°C) and high irradiance (450 and 850 μmol m-2 s-1). Results indicated that wheat plants showed more tolerance to low temperature. Increased tolerance in cold-treated plants was achieved through enhancement in antioxidant system activity. Plants treated with light intensity at 850 μmol m-2 s-1 showed the highest level of stress leading to lower maximal quantum yield of photosystem II (PSII) (Fv/Fm) values. In contrast, the light intensity at 450 μmol m-2 s-1 did not reduce significantly the maximal quantum yield of PSII. This may be attributed to the enhancement of catalase (CAT) activity and anthocyanin synthesis (screening of photoradiation in epidermis cells), and consequently further protection of PSII from photodamage.

In this study, the influence of hydroponically applied (0.1, 1 and 10mg l-1) and foliar-applied (10mg l-1) Na2SeO3 on the some physiological characteristics of Melissa officinalis L. was investigated. The results indicated that the root application of 10mg l-1 Se could decrease shoot fresh and dry mass, and caused an improved lipid peroxidation in hydroponically grown lemon balm. Se supply at 10mg l-1 in lemon balm exhibited a significantly positive effect on accumulation of total chlorophyll, and raised the activity of catalase, but these mechanisms could not ameliorate the negative effect of Se toxicity on productivity, as was indicated by a higher malondialdehyde concentration. Our results indicated that for biofortification program with lemon balm, the application of Se as selenate at low concentrations (0.1 and 1mg l-1) would be more beneficial because it favored shoot biomass growth. In contrast, the results from field experiment indicated that foliar-applied Se (10mg l-1) was favorable for biomass accumulation in lemon balm. In this work, the foliar application of selenium induced higher activity of phenylalanine ammonia-lyase as well as the higher total phenol content, which appear to act as protective compounds. It was concluded that foliar applications to lemon balm at 10mg Se l-1 can effectively cause a significantly higher growth rate, improve Se content and phenolic compounds.