Influence of the electromagnetic fields on some biological characteristics of Lepidium sativum L.
Life on earth has evolved in a sea of natural electromagnetic fields. Over the past century, this natural environment has sharply changed with introduction of a vast and growing spectrum of man-made electromagnetic fields .
Magnetic field can affect chemical bonds between adjacent atoms with consequent production of free radicals . Recent findings suggest that ELF-magnetic field can increase free radical life-span of cell [13,28]. A potential link between EMFs and its effects on living organisms is the fact that EMFs cause an oxidative stress that is, increase in the activity, concentration and lifetime of free radicals . Electromagnetic fields affect biological systems as the kind of abiotic stress .
In plants affected by stress, a response is induced by changes in the plant metabolism, growth and general development . Many studies have reported the effects of magnetic fields on variety of agriculturally important plants.
Alexander et al. found that seed germination of onion and rice is accelerated if exposed to a weak electromagnetic field for 12 h and further, the seedlings showed significantly increased fresh and dry weight.
Bitonti and collaborators showed that exposure of Zea mays seedlings to a continuous electromagnetic field (DC) for 30 h induced stimulation by about 30% in the rate of root elongation compared with the controls . Oxidative stress was induced when Duckweed (Lemna minor L.) exposed to EMFs for two hours
In meristematic cells in Allium ceppa which seeds were exposed to EMFs, mitotic index and mitotic aberration such as lagging chromosomes, vagarant, chromosome stickness and distributed anaphase was induced (Khalec et al., 2009). EMFs also alter gene expression, protein biosynthesis, enzyme activity and cell reproduction .
Lepidium sativum L. (Garden cress) is an annual herb, belonging to Brassicaceae family. It is a fast-growing, edible plant botanically related to watercress and mustard and sharing their peppery, tangy flavor and aroma. Seeds, leaves and roots are economically important. This important green vegetable consumed by human beings, most typically as a garnish or as a leaf vegetable .
This study considers the effects of EMFs as abiotic stress on the seed germination, seedling development, mitotic index, some physiological characters and leaf peroxidase activity as the antioxidant enzyme.
MATERIALS AND METHODS
Electromagnetic field exposure:
Exposure to EMFs was performed using a locally designed EMF generator. The electrical power was provided by a 220 V AC power supply (ED-345BM, China) with a variable voltage, current and fixed frequency (60 Hz). This system consisted of one handmade coil, cylindrical in form, made of polyethylene 12 cm in diameter and 50 cm in length. The coil was not shielded for electrical field and the seeds were exposed to both magnetic and electric fields generated by the coils.
Seeds preparation and treatment:
Lepidium sativum L. were supplied by Pakan bazr institute, which guarantees high seeds quality and homogeneity. The healthy uniform seeds were selected and divided in to wet and dry seeds groups. Three replicates were used in the experiment with 30 seeds in each treatment. In the case of wet treatment, the seeds were soaked in distilled water for 7 and 14 hours and then placed in the middle of a horizontally fixed coil. The wet and dry seeds were exposed to EMFs by a magnitude of 3.7 mT, for 30 and 60 min. On the first day of treatment the percentage of germination was measured (Seed germination was completed for all of the treatments in the first day). Fourteen-day-old plants were then used for measurement of growth parameters (leaf fresh weight, shoot and root length, number of lateral roots) and chlorophyll a, b, carotenoid leaf protein content and leaf peroxidase activity and three day old plants were used for measurement of mitotic index.
The 3 day old root meristem tissue samples from germinated seeds (using only roots reached about maximum 5 mm length) were used to prepare microscope slides. For preparation of all dividing stages, root tips were fixed in Camoy's fixative without pre-treatment. Preparation of slides from the fixed root tips was done following acetocarmine squash technique. The cell mitotic index were examined and counted microscopically on squashes. The mitotic index is able to give the percentage of dividing cells in every sample:
M. 1% = (total cells in division/ total cells analyzed) x 100
Determination of photosynthetic pigments:
Rate of photosynthetic pigments estimated according to the method of Lichtenthaler et al., . Fresh leaves (0.1 g) were homogenized in 80% acetone and centrifuged at 10,000xg for 10 min. The supernatant was subjected to spectrophotometeric analysis of 646, 663 and 470 nm respectively. Chlorophyll a, chlorophyll b, and carotenoid content was determined and expressed in mg/ g FW.
Chl. a, Chl. b and carotenoid contents were calculated using the following formulas:
Chl. a = (12.21 (A663) - 2.81 (A646)) x volume of supernatant (ml) / 1000x sample weight (g).
Chl. b = (20.13 (A646) - 5.03 (A663)) x volume of supernatant (ml) / 1000xsample weight (g).
Car. = [(1000A470 (1000A470 - 3.27[chl a] - 104[chl b])/227] x volume of supernatant (ml) / 1000 x sample weight (g).
Protein content assay:
Frozen leaves (0.5 g fresh weight) were homogenized in 5 ml Tris- Glycine buffer (pH 8.3). The homogenate was then centrifuged at 12000x g for 10 min. All operations were performed at 4 [degrees]C. Protein contents were determined by the method of Bradford (1976) using bovine serum albumin (BSA) as a standard .
The peroxidase activity was measured in a reaction mixture consisting of acetate buffer (0.2 mM, pH 4.8), hydrogen peroxide (0.1 mM), benzidine (0.04 M) and enzyme extract. Enzyme activity was measured by a spectrophotometer (Genway Genova) at 530 nm .
All of the experiments were carried out with at least three independent repetitions. Data were then evaluated with one-way analysis of variance combined with Tukey's multiple-comparison test (Sigma Stat, SPSS Science, Chicago, IL). The differences between each treatment in comparison with the others were considered significant at the P < 0.05 level figures. The results were expressed as mean values [+ or -]standard error.
Seed germination speed was significantly different among electromagnetic fields treatments. As a whole, electromagnetic treatments obviously increased germination in different electromagnetic exposure periods, but the differences were greatest when the seeds were soaked in water for 7 and 14 hours and exposed to electromagnetic field for 1 hour. At higher duration, germination was higher (Table 1).
Mitotic index, root length and number of lateral roots:
EMFs increased the mitotic index, root length and the number of lateral roots. The highest value of mitotic index belonged to dry and wet pretreated seeds with 60 minutes exposure time. The highest root length occurred in plants grown from 7 and 14 hour wet pretreated seeds with 3.8 mT for 60 minutes. EMFs exposure also caused significant differences in the mean of lateral roots. In this case the most number of lateral roots occurred in the wet and dry pretreated seeds with 60 minutes of EMFs exposure time in compared to control plants (Table 2).
The effect of EMFs on the shoot system growth was highly perceptible. EMFs increased the shoot length. There was significant difference for all treated samples compare to control plants. The wet and dry treated seeds with 60 minutes exposure time had longer shoot length compare to control group (Table 2).
Wet and dry weight:
Electromagnetic fields increased dry and wet weight of Lepidium sativum L.. The plants grown from 7 and 14 hours wet pretreated seeds with 60 minutes of EMFs exposure time showed the most level of the fresh and dry weight that had the significant difference compare to control, but there was no significant difference between control and dry treated seeds (Table 2).
The results of the present study indicated that there was no significant difference in chlorophyll a and chlorophyll b content in plants grown from wet and dry pretreated seeds in comparison with control plants, but this difference was significant in caretonoid concentration. Wet treated seeds had the most carotenoid concentration compare to the other groups and control (Table 3).
Electromagnetic fields increased protein content of Lepidium sativum L.. Results showed that protein content increased in the treated plants in comparison with the control group. Treated seeds with 1 hour exposure time at 3.8 mT had more protein content than those with 0.5 hour exposure time and control (Table 3).
Peroxidase activity increased in the treated plants in comparison with the control group. Maximum and minimum leaf peroxidase activities were observed in the control and 14 hours wet pretreated seeds with 1 hour exposure time, respectively (Table 3).
Results obtained for Lepidium sativum L. was according with other studies about the influence of magnetic field on several seed germination and plant growth which reveal that magnetic treatment produces: an improvement of percentage and rate of germination of exposed seeds. Florez et al. 2007 reported the positive effects of magnetic field treatments on germination rate and growth. The possible reason for intensification of germination may be increasing metabolism in irradiation seeds and increase in substance consumption and more water absorption under effect of EMFr .
The results showed that the effect of electromagnetic fields on Lepidium sativum L. growth in terms of root length, number of lateral roots and mitotic index was more than control. Wet condition with 1 hour exposure time increased growth and development of roots. Growth rate is regulated by the combined activity of two linked processes, expansion and cell production (Beemster Gerrit and Baskin Tobias, 1998). We found that magnetic fields caused significant increase in the cell division in root meristem cells. Therefore electromagnetic fields probably enhance the root length by stimulating the tip root cells division.
Leaf protein content was higher in EMFs pretreated plants. Magnetic application could induce the protein synthesis in plants and it might be the reason of more accumulation of protein in leaf which is consistent with the findings of this study. Other study has also reported higher protein content in magnetic field exposed Cucumis sativum seedlings .
Fresh and dry biomass weight of plants grown from exposed grains were increased significantly compare to the control plants, which may be due to higher rate of protein synthesis in pretreated plants. . indicated that electromagnetic fields increased enzymes activity and protein contents and led to enhance biomass of plants. Farzpour et al., also reported that electromagnetic fields caused significant increase in dry and wet weight of Valerian seedlings.
Our results demonstrated that electromagnetic fields increased carotenoid content and peroxidase activity especially in wet and dry pretreated seeds with 60 minutes electromagnetic exposure time. As the exposure time increased, the rate of carotenoid and peroxidase activity enhanced, but electromagnetic fields did not affect chlorophyll a and chlorophyll b content. Similar experiment was reported electromagnetic fields of low intensity (1 mT) caused significant increase in carotenoid content of Satureja bachtiarica L. .Recent findings suggest that magnetic field may extend the lifetime of the free radical and its potential of damage could be exaggerated
. Carotenoids constitute the first line of defense against [sup.1]O2 toxicity. They are able to quench this ROS and also directly quench triplet chlorophylls, the major source of [sup.1]O2 in plant leaves [8,12,27].Therefore increase in carotenoid content probably caused the stability of chlorophyll a and chlorophyll b content. Another main protective role against free radicals is increase of the activity of ROS scavenging enzymes, e.g., SOD, CAT, and PO . Scavenging of H2O2 is conducted by peroxidase and other H2O2-consuming enzymes. Therefore, a higher concentration of carotenoids and PO activity suggest the responses of EMFs pretreated seedlings to oxidative stress and free radicals to protect plants against ROSs (reactive oxygen species).
The exposure of low electromagnetic fields has elicited detectable responses on Lepidium sativum L. in their early ontogenetic stages: the significant stimulatory influence on plants growth was gained, the average of mitotic index, root and shoot length values, fresh and dry tissue mass, carotenoid and protein content and peroxidase activity, being enhanced for all exposure durations and as the exposure time increased the amount of these parameters enhanced in plants grown from dry and wet pretreated seeds. Electromagnetic fields also had the slight stimulatory influence (EMFs increased chlorophyll a and b) on the chlorophyll a and b that was not significant.
Received 14 Feb 2014
Received in revised form 24 February 2014
Accepted 29 March 2014
Available online 14 April 2014
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Elham Bagheri Abyaneh, Ahmad Majd, Sayeh Jafari, Golnaz Tajaddod, Fahimeh Salimpour
Department of Biology, Faculty of Biological Sciences, North-Tehran Branch, Islamic Azad University, Tehran, Iran.
Corresponding Author: Elham Bagheri Abyaneh, Department of Biology, Faculty of Biological Sciences, North-Tehran Branch, Islamic Azad University, Tehran, Iran.
Table 1: The effect of low frequency electromagnetic fields on seeds germination of Lepidium sativum L. Seed EMF exposure 18th hour 20th hour condition time Control -- 30 [+ or -] 36.67 [+ or -] 5.77 a 6.66a Dry 30 min 33 [+ or -] 53.33 [+ or -] 3.33 a 8.81 abd Dry 60 min 63.33 [+ or -] 80 [+ or -] 8.81 abc 10 bcde 7 h wet 30 min 40 [+ or -] 66.67 [+ or -] 5.77 ab 3.33 abcde 7 h wet 60 min 73.33 [+ or -] 90 [+ or -] 3.33 bc 5.77 cde 14 h wet 30 min 60 [+ or -] 73.33 [+ or -] 10 abc 8.81 de 14 h wet 60 min 76.67 [+ or -] 100 [+ or -] 8.81 c 0 e Seed EMF exposure 22nd hour condition time Control -- 70 [+ or -] 5.77 a Dry 30 min 76.67 [+ or -] 8.81 abc Dry 60 min 93.33 [+ or -] 6.66 abc 7 h wet 30 min 86.67 [+ or -] 8.81 abc 7 h wet 60 min 100 [+ or -] 0 bc 14 h wet 30 min 93.33 [+ or -] 3.33 abc 14 h wet 60 min 100 + 0 c Data are means [+ or -] SE, n - 3. Different letters refer to significant differences according to Tukey test (P < 0.05). Table 2: The effect of low frequency electromagnetic fields on seedlings growth, fresh and dry weight of Lepidium sativum L Seed EMF Mitotic Root Number of condition exposure index length lateral roots time (cm) control -- 2.36 [+ or -] 3.77 [+ or -] 4.60 [+ or -] 0.06 a 0.22 a 0.37 a Dry 30 min 2.54 [+ or -] 3.81 [+ or -] 4.97 [+ or -] 0.05 abce 0.41 ab 0.58 a Dry 60 min 2.7 [+ or -] 4.37 [+ or -] 8.23 [+ or -] 0.03 bcde 0.08 abc 0.44 bcd 7 h wet 30 min 2.61 [+ or -] 4.18 [+ or -] 6.23 [+ or -] 0.05 cde 0.11 abc 0.38 abcd 7 h wet 60 min 2.82 [+ or -] 4.91 [+ or -] 7.90 [+ or -] 0.03 de 0.27 bc 0.66 cd 14 h wet 30 min 2.72 [+ or -] 4.33 [+ or -] 6 [+ or -] 0.02 e 0.21 abc 0.24 abc 14 h wet 60 min 3.08 [+ or -] 5.2 [+ or -] 8.73 [+ or -] 0.04 f 0.13 c 0.80 d Seed EMF Shoot Fresh Dry weight condition exposure lenght (cm) weight (mg) (mg) time control -- 1.6 [+ or -] 85.91 [+ or -] 4.92 [+ or -] 0.02 a 7.745 a 0.62 a Dry 30 min 2.33 [+ or -] 92.20 [+ or -] 6.240 [+ or -] 0.17 bcdef 10.25 ac 0.2031 ad Dry 60 min 2.46 [+ or -] 101.1 [+ or -] 7.01 [+ or -] 0.14 cdef 8.163 abc 0.67 abd 7 h wet 30 min 2.26 [+ or -] 122.3 [+ or -] 12.92 [+ or -] 0.8 def 4.768 abc 2.92 bcde 7 h wet 60 min 2.62 [+ or -] 136.9 [+ or -] 13.65 [+ or -] 0.18 ef 4.729 bcd 1.27 cde 14 h wet 30 min 2.38 [+ or -] 127.8 [+ or -] 12.13 [+ or -] 0.1 f 8.852 cd 0.88 de 14 h wet 60 min 3.33 [+ or -] 169.5 [+ or -] 15.19 [+ or -] 0.03 g 7.075 d 0.77 e Data are means [+ or -] SE, n = 3. Different letters refer to significant differences according to Tukey test (P < 0.05). Table 3: The effect of electromagnetic fields on Chlorophyll a, Chlorophyll b, carotenoid, protein content and peroxidase activity of Lepidium sativum L. Seed EMF Chlorophyll a Chlorophyll b condition exposure (mg/g fW) (mg/g FW) time Control -- 0.48 [+ or -] 0.23 [+ or -] 0.02 a 0.01 a Dry 30 min 0.56 [+ or -] 0.31 [+ or -] 0.04 a 0.04 a Dry 60 min 0.58 [+ or -] 0.33 [+ or -] 0.01 a 0.02 a 7 h wet 30 min 0.6 [+ or -] 0.30 [+ or -] 0.02 a 0.02 a 7 h wet 60 min 0.64 [+ or -] 0.34 [+ or -] 0.008 a .007 a 14 h wet 30 min 0.61 [+ or -] 0.31 [+ or -] 08 a 0.03 a 14 h wet 60 min 0.62 [+ or -] 0.35 [+ or -] 0.01 a 0.02 a Seed EMF Carotenoid Protein condition exposure (mg/g FW) content time (mg/ g FW) Control -- 0.22 [+ or -] 1.87 [+ or -] 0.02 abcdef 0.3 a Dry 30 min 0.22 [+ or -] 2.27 [+ or -] 0.02 abcdef 0.09 a Dry 60 min 0.23 [+ or -] 2.56 [+ or -] 0.008 bcdef 0.27 ac 7 h wet 30 min 0.24 [+ or -] 2.12 [+ or -] 0.02 cdef 0.24 a 7 h wet 60 min 0.26 [+ or -] 3.98 [+ or -] 0.006 def 0.22 bcd 14 h wet 30 min 0.26 [+ or -] 3.71 [+ or -] 0.002 ef 0.36 cd 14 h wet 60 min 0.27 [+ or -] 4.87 [+ or -] 0.0099 f 0.22 d Seed EMF Peroxidase condition exposure activity time (OD /min. g FW) Control -- 1.5 [+ or -] 0.23 a Dry 30 min 2.9 [+ or -] 0.45 a Dry 60 min 5.78 [+ or -] 0.08 abc 7 h wet 30 min 5.5 [+ or -] 1.32 abc 7 h wet 60 min 10.17 [+ or -] 0.97 bcd 14 h wet 30 min 11.20 [+ or -] 0.91 cd 14 h wet 60 min 12.77 [+ or -] 2.54 d Data are means [+ or -] SE, n = 3. Different letters refer to significant differences according to Tukey test (P < 0.05).
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|Author:||Abyaneh, Elham Bagheri; Majd, Ahmad; Jafari, Sayeh; Tajaddod, Golnaz; Salimpour, Fahimeh|
|Publication:||Advances in Environmental Biology|
|Date:||Feb 14, 2014|
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