فصلنامه فرآیند و کارکرد گیاهی
سال هفتم شماره 6 (پیاپی 28، Feb and Mar 2018)

In this experiment, wheat plants were exposed to drought stress during seed development then we worked on the obtained seeds. The seed mitochondrial ultra-structure, and antioxidant enzymes in seedling were investigated after exposure to seed accelerated ageing. Drought stress during seed development induced some changes in mitochondrial ultra-structure. Encountering seed development to drought stress decreased antioxidant enzymes activity and increased H2O2 in the seedling. Seed accelerated ageing declined antioxidant enzyme activity and increased malondialdehyde. Mitochondrial ultra-structure also showed heavy damage after accelerated ageing. Most damages in mitochondrial ultra-structure were observed in the seeds obtained from drought-stressed plants then exposed to accelerated ageing. A swollen form of mitochondria with less crista was observed in the seed that exposed to accelerated aging. Damage to mitochondria may be the main cause for seed ageing. However, the activity of antioxidant enzymes is a key factor in order to repair the damage and inhibit the lipid peroxidation resulted in maintaining cell membrane integrity in aged wheat seeds.

Silybum marianum is an important medicinal plant with high antioxidant properties. Static magnetic field (SMF) is a kind of abiotic stresses which can affect growth and antioxidant capacity of medicinal plants. In this research, the effects of SMF on total phenolic and flavonoid contents, radical scavenging activity, and anatomical alterations were investigated in S. marianum seedlings. Five-day-old seedlings were treated with different intensities of SMF (0, 2, 4 and 6 mT) for one hour, and then were irrigated with 1/2 Hoagland solution for four weeks. Results showed that SMF up to 4 mT increased significantly fresh weight, dry weight, leaf area, relative water content (RWC), root length and then decreased these parameters at 6 mT. At 4 mT, SMF caused an 125, 132.73 and 52.19% increase of dry weight, leaf area and root length as compared to control, respectively. Metaxylem number and size, aerenchyma formation and stele diameter improved under SMF. Lipid peroxidation (MDA) decreased especially at 4 mT, although H2O2 level increased in S. marianum shoots. SMF also induced total phenolic (93.89%) and flavonoid contents (36.43%), and decreased IC50 values (43.01%) especially at 4 mT in leaves. It suggests that SMF at proper frequency could improve antioxidant capacity of plant cells by regulation of H2O2 level and membrane stability.

Salicylic acid (SA) is a key molecule that alleviates abiotic stress in many plant species. In this study, the role of SA was examined to moderate lead (Pb) toxicity in the basil (Ocimum basilicum). The experimental design was a randomized complete block design with 4 levels of PbNO3; 0 (control), 100, 200 and 300 mg kg-1 of soil as the first factor, and the foliar application of SA at 3 levels of 0, 50 and 100 mL L-1 comprised second factor that were applied with four repetitions. The experiment was conducted during 2013 at research greenhouse of the Zabol University. Addition of Pb at a rate of 300 mg.kg-1 significantly reduced the carotenoids by 45.5 percent and organic acids by 49.3 percent, while it caused an increase in anthocyanins, flavonoids, electrolyte leakage and antioxidant enzymes, including lipoxygenase and glutathione peroxidase. In addition, SA spraying had a significant influence on all traits. In this study, the interaction effects between SA and Pb was significant on carotenoids, anthocyanins, flavonoids, electrolyte leakage, organic acid, and lipoxygenase and glutathione peroxidase, and play a moderating role and reduce the harmful effects of Pbtoxicity. The results of this experiment suggested that the application of SA in basil caused a reduction in oxidative damage originated by Pb toxicity and induce the synthesis of photosynthetic pigments, such as carotenoids.

Linum usitatissimum L. is one of the economically important oilseed crops and salt stress is one of the major environmental challenges affecting several physiological processes in plants. The present investigation was carried out to study the effects of NaCl on some physiological and biochemical responses in two cultivars of L. usitatissimum. Twenty-one-day-old-plants were exposed to salt stress (0 and 150 mM) for 21 days. Results showed that salinity increased proline, phenol and flavonoid contents and total antioxidant capacity (based on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Ferric reducing antioxidant power (FRAP) assays) in flax cultivars. Levels of oxidative stress parameters, such as Malondialdehyde (MDA) and other aldehydes, content of Na+ and Cl- and peroxidase (POD) enzyme activity were increased in NaCl-treated plants. The content of soluble protein was elevated and decreased in TN-97-28 and TN-97-106 cultivars, respectively. On the other hand, other antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APOX) were decreased and increased in TN-97-28 and TN-97-106 cultivars, respectively. It might be concluded that various cultivars have different mechanisms to diminish negative impacts of salinity stress.

Barley crop grown in semiarid areas may experience water deficit especially during grain filling that makes them more dependent on stem water-soluble carbohydrates (WSC). Fructans are the most important reserved carbohydrates. A pot experiment was undertaken at Shahid Chamran university in the duration of 2010-2011 growing seasons to investigate the accumulation and loss of WSC and the activity of fructan-metabolizing enzymes under water stress in four barley (Hordeum vulgare L.) cultivars namely Nimruz, Jonub, Nosrat and Torkaman. Cultivars were different in WSC-related traits such as WSC concentration (WSCc) at anthesis, maximum WSCc and rate of WSC accumulation in ten-day period after anthesis. Water withholding elevated WSC remobilisation efficiency. The activity of sucrose:sucrose 1-fructosyl transferase (1-SST; EC 2.4.1.99) harmonized the rate of WSCc increase in cultivars. The change in fructan 1-exohydrolase (1-FEH; EC 3.2.1.80) activity on the fifteenth day postanthesis was along with the change in stem reserve remobilisation. Considering acid invertase (EC 3.2.1.26) activity, a significant difference was observed between cultivars on the fifteenth day post anthesis under water-stressed conditions. Cultivars showed different manners in use of current photosynthesis and stem reserves that could be an important reason in different decreases in grain weight affected by water stress.

Despite the numerous studies on the effect of the magnetic field on plants, the exact mechanism of these effects has not yet been determined. The aim of this study was to compare the effect of magnetic field on growth and photosynthetic characteristics of two almond species (Amygdalus scoparia and A. eburnea). For this purpose, 21-day-old almond plants were affected by 10 mT static magnetic field for 4 days, 5 hours each day. The fresh weight, dry weight, water content and length of ground and aerial parts were measured. Also, the number of leaves, leaf area, photosynthetic pigments content and finally total phenol content were investigated. The results showed that the fresh weight, water content and length of the plant in the shoot increased compared to the control samples, but the number of leaves and the size of the leaf area did not change. In addition, the content of chlorophyll and carotenoid decreased, but the amount of phenolic compounds increased in A. eburnea. It seems that static magnetic fields have receptors in the almond plant that act like phytochromes and induce relevant responses.

Stevia rebaudiana Bert (Asteraceae) is herbaceous plant with sweet leaves, which are the source of sweetener products. The present study focuses on effects of different combination of plant growth regulators on callus induction, callus cell growth and regeneration and volatile constituents from callus of stevia in tissue culture condition. The results of present study showed callus formation promoted in all of media contained phytohormones of different auxin/cytokinin based combinations. However, NAA/BA combinations are significantly more effective to callus initiation and the highest amount of callus was obtained in medium supplemented with 1.5:2 mg/L of NAA/BA. It was revealed that shoot induction in callus was happen at hormonal treatments as IBA/BA and IBA/KIN (0.5:1.5 mgl-1). High rooting obtained in media supplemented with NAA/KIN (1.5:0.5 mgl-1). The results of GC-MS analyses of volatile constituents of calli showed that the callus oil obtained in media supplemented with NAA/Kin (1.5:0.5 mgl-1). The NAA/Kin treatment with 1:0.5 mgl-1 concentration was dominated with squalene (40.50%) as main compound. The callus formed in media contained NAA/BA was enriched with Tricosane (38.57%). In addition, phytol (11.69%, 6.92%) was regarded as major constituent of the oil obtained from cultures supplemented with IBA/Kin and IBA/BA, respectively. It was concluded that there was a considerable differences in the essential oil profile of callus induced from different hormonal combinations. It is thought that various hormonal treatments may be tending to changes in metabolic pathways.

Phytoremediation counts as a major method for future which essentially needs resistance to contaminating agents. We pretreated the plants (Salix babylonica, as a model plant in phytoremediation of polluted waters) by sodium cyanide (0, 3 and 5 mg CN- L-1) to induce resistance with regard to acclimation and then examined their resistance to higher concentrations of cyanide. Accordingly, some of the resistance- related physiological parameters were measured. The results showed that the pretreatment increased the resistance up to 3 folds more than toxicity threshold. It induced the superoxide dismutase activity and ion leakage from roots. Dehydrogenase activity, reducing capacity of the roots and chlorophyll were decreased in pretreated plants. Results also showed that no difference was between the control and pretreated plants in the uptake of cyanide from media. The induced resistance via cyanide acclimation could be attributed to physiological responses such as higher activities of antioxidants and not to prevention of cyanide uptake into the cells.