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Influence of the electromagnetic fields on some biological characteristics of Lepidium sativum L.

INTRODUCTION

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 [1].

Magnetic field can affect chemical bonds between adjacent atoms with consequent production of free radicals [17]. 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 [21]. Electromagnetic fields affect biological systems as the kind of abiotic stress [7].

In plants affected by stress, a response is induced by changes in the plant metabolism, growth and general development [15]. Many studies have reported the effects of magnetic fields on variety of agriculturally important plants.

Alexander et al.[2] 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 [4]. 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 [16].

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 [24].

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.

Mitosis 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., [14]. 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 [5].

Peroxidase activity:

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 [11].

Statistical analysis:

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.

Results

Seeds germination:

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).

Shoot length:

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).

Photosynthetic pigments:

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).

Protein content:

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:

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).

Discussion:

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 [22].

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 [19].

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. [10]. 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. [20].Recent findings suggest that magnetic field may extend the lifetime of the free radical and its potential of damage could be exaggerated

[6]. 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 [23]. 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).

Conclusion:

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.

ARTICLE INFO

Article history:

Received 14 Feb 2014

Received in revised form 24 February 2014

Accepted 29 March 2014

Available online 14 April 2014

REFERENCES

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[18] Radhakrishnan, R. and B.D.R. Kumari, 2012. Pulsed Magnetic Field: A Contemporary Approach Offers to Enhance Plant Growth and Yield of Soybean. Plant Physiology and Biochemistry, 51: 139-144.

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[22] Shabrangi, A. and A. Majd, 2009. Comparing Effects of Electromagnetic Fields (60 Hz) on Seed Germination and Seedling Development in Monocotyledon and Dicotyledons. Progress in Electromagnet. Res. Symp. Proceed, 18-21.

[23] Sreenivasulu, N., B. Grimm, U. Wobus and W. Weschke, 2000. Differential Response of Antioxidant Compounds to Salinity Stress in Salt Tolerant and Salt-sensitive Seedlings of Foxtail millet (Setaria italica), Physiol. Plant, 109: 435-442.

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[25] Malaric, M.K. and B. Pevalek-Kozlina, 2007. Exposure to Radiofrequency Radiation Induces Oxidative Stress in Duckweed Lemna minor L.. Sci Total Environ., 388(1-3): 78-89.

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[28] Yokus, B., D.U. Cakir, M.Z. Akdag, C. Sert and N. Mete, 2005. Oxidative DNA Damage in Rats Exposed to Extremely Low Frequency Electromagnetic Fields. Free Radic Res., 39: 317-323.

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.

E-mail: e.bagherii@yahoo.com
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
Article Type:Report
Geographic Code:7IRAN
Date:Feb 14, 2014
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