فصلنامه فرآیند و کارکرد گیاهی
سال دوم شماره 1 (پیاپی 3، بهار 1392)

Several studies have shown that magnetic fields can exert an influence on a large variety of cellular functions; however, the exact mechanism of this interaction in living cells is still unclear. One possible explanation for the adverse effects of magnetic fields on living organisms is oxidative stress resulting from an increase in the production of reactive oxygen species through iron as a mediator. Oxidative stress also brings about changes in enzyme activity, gene expression, and the release of calcium from intracellular storage sites. In the present study the effects of 30 mT static magnetic field and a 10 KHz electromagnetic field on the root and shoot length, activity of antioxidant system, membrane integrity, and the total of calcium and iron content of wheat (Triticum aestivum L.) at vegetative stage were estimated. The results showed that magnetic field caused promotion of antioxidant system, maintenance of membrane integrity and changes in calcium and iron balance, compared to the control group. These effects vary depending on many factors e.g., the sort of magnetic field and the plant organs being exposed to the field.

Drought stress is one of the main stresses that inhibits the growth of plants due to mainly disturbance of the balance between production of reactive oxygen species and antioxidant defense and thereby causing oxidative stress. Evaluation of medicinal plants tolerance to drought stress in order to plant them in dry region is very important. In this research, oxidative parameters of drought stress induced by different concentration of polyethylene glycol solutions in Nigella plant were investigated. To control experimental conditions including the inhibitory effects of the other factors such as soil nutrition the hydroponic medium was used. In this study, drought stress significantly increased the H2O2 content, lipid peroxidation and lipoxygenase activity which were showed the oxidative stress induced by drought in Nigella plants. Study of the defense mechanisms, through the measurement of the antioxidant enzymes activities indicated that drought stress increased the activity of ascorbate peroxidase, catalase and guaiacol peroxidase. However in this research, we observed that the increment in drought level had no significant effects on catalase and guaiacol peroxidase activity. It seemed that in this investigation the increment of proline might be related to both osmotic and antioxidant characteristic of this compound. Increase of lipid peroxidation and H2O2 content in drought stress showed that the scavenging and quenching of ROS were out of the plant ability and the induction of plant defense mechanism against oxidative damages was not effective.

Drought stress is considered as a limiting factor for plant productions; therefore, many compounds have been applied to minimize the harmful effects of stress. In this study, the effect of paclobutrazol, a triazole growth regulator, on morphological and biochemical parameters of Brassica napus L. under in vitro drought stress was investigated. First, the seeds of B. napus L. were sterilized and then were cultured in MS medium supplemented with mannitol at percentages of 0, 4 and 8)various levels of drought) and 0, 10 and 20 ppm paclobutrazol. Also, B. napus stem explants were cultured in MS medium containing rooting and callogenesis hormones with mannitol (0, 4, 8%) and paclobutrazol (0, 10 ppm). After 4 weeks, results showed stem and root length, stem and root dry weight, chlorophyll a, total chlorophyll, carotenoids, rooting and callogenesis percentage and callus fresh weights significantly decreased but lipid peroxidation, reducing sugar and proline increased in seedlings which were under drought stress. Decreased peroxidation of lipids and increased the root length, stem and root weight, reducing sugars, proline, photosynthetic pigments and protein of the seedlings which were treated with both paclobutrazol and drought stress were also observed, which was probably the indication of reduction of the damage caused by stress in these seedlings. Therefore paclobutrazol especially in concentrations of 10 ppm was more effective in relieving stress damages caused by drought stress in B. napus L.

Plant growth promoting rhizobacteria are beneficial bacteria that increase growth of plants and induce resistance to various stresses. SO2 air pollution is one of these stresses that is known as a strong damaging air pollutants. Persian clover is one of legume family plants that consider as a forage crop and can form symbiosis with Rhizobium bacteria. In this study, the effects of Rhizobium (native and standard strains) on amounts of photosynthetic pigments and phosphorus and potassium elements of Persian clover under different concentrations of SO2 (0, 0.5, 1, 1.5 and 2ppm) were evaluated. The results showed that inoculation has beneficial effects on the amounts of photosynthetic pigments and phosphorus and potassium content in compared with non-inoculated plants. High concentrations of SO2 (1, 1.5 or 2ppm) caused a significant decline in the amounts of photosynthetic pigments and phosphorus and potassium elements of clover plant in compared to the control plants, however low concentration of SO2 (0.5ppm) had positive effects on measured parameters. Inoculation of Persian clover with two strains of Rhizobium decreased negative effects of high concentrations of SO2 on the amounts of photosynthetic pigments and phosphorus and potassium elements. The highest values of these parameters were measured in combination of the local strain plus 0.5ppm of SO2. It was suggested that Rhizobium could increase plant resistance and tolerance against abiotic stresses such as air pollution.

Salinity is an environmental stress and is the main limiting factor in the efficiency of agriculture products in the world. Salsola arbuscula is a halophyte plant and resistant to high salinity, therefore, this investigation was aimed to study the tolerance mechanisms to salt stress with the changes in growth parameters and microscopic study of callus. To achieve our purpose, firstly, seeds were cultured in the MS medium and after 2months; callus was produced from root explants in the different media. Calli were then transferred to the previous culture medium with different concentrations of NaCl salt (0, 100, 200, 300, 400 mM) and after one month, fresh and dry weight, relative growth rate (RGR), relative water content (RWC), sensitivity index (SI) and cell dimensions were measured. Results showed that the best medium to induce callus production were medium of MS with 2,4D (1mg/L) + Kin(1mg/L). With increasing of NaCl concentration, callus color changed and necrosis occurred higher and faster. Also with increasing NaCl concentration fresh and dry weight, relative growth rate, relative water content and sensitivity index were decreased and fresh weight decreased more than dry weight. length, width, and area of the cells decreased as the stress was increased. Salt effect on cells length was higher than width by decreasing of the size and the growth of the cells.

Serpentine soils have some unusual properties such as low Ca and high Mg concentrations and also some of the heavy metals which are the inducers of high plant endemism. One of the possible causes of endemism could be Ca sensitivity and high Mg requirement. Since Mg and Ca interact in uptake and transport by plants, the effect of Mg in Ca sensitivity was studied in Alyssum inflatum which is a serpentine endemic from western Iran and its Ca sensitivity has proved. The seeds were harvested from thier natural habitats and the plants were cultivated in greenhouse using of a solution culture on chemically inert substrate of Perlite. A modified one forth strength Hoagland solution was used and different concentrations of Ca and Mg were achieved. To determine the viability of plants, the appearance of plants including wilting and drying of the shoot, and root cell death were determined using of Evan’s blue staining. The results showed that the plants were sensitive to high concentrations of both of cations of Ca and Mg. Effect of Ca/Mg ratios on survival of plants was important provided that the absolute concentrations of the elements were low. The results suggested that one of the endemism reasons on serpentine soils was Ca sensitivity while high Mg concentrations did not decrease the sensitivity.

In order to evaluate some biochemical responses of bread wheat (Shiraz cultivar) and durum wheat (Yavarous cultivar) to late season water stress and different auxin and cytokinin levels, a field experiment was carried out in research farm of the collage of Agriculture, Shiraz University during 2010-2011 growing season using a split split factorial as randomized complete block design with three replications. Irrigation regime (normal and cutting off water at anthesis), wheat cultivars (Shiraz and Yavarous) and factorial combination of auxin (0, 20 and 40 mg/L) and cytokinin (0, 50 and 70 Mm) levels were considered as main, sub and sub sub plats, respectively. The results showed that flag leaf proline and catalase content were increased linearly upon cutting off irrigation at anthesis; while, proline and catalase content did not show any significant changes after anthesis under normal irrigation conditions. Moreover, proline content in Yavarous cultivar was found to be significantly greater than Shiraz cultivar. Among cytokinin concentrations, the highest catalase activity was obtained from control treatment. As cytokinin concentrations were increased, catalase activity was decreased under well watered conditions. Peroxidase activity was increased under irrigation cut off conditions, and was enhanced with time lapse from anthesis. Chlorophyll a, b, carotenoid and total of foliage leaf were greater under cut off irrigation conditions. Deep understanding of biochemical responses of wheat cultivars to late season drought stress and its interaction with plant growth regulator needs further complimentary research.