INTRODUCTION:

Life originated underwater. Therefore, early organisms have evolved adaptive strategies for the aquatic environment. Reproduction in them occurs by spores. However, with the shrinking of oceans, organisms moved out of the water. Hence, they needed a tough structure to protect the nascent embryo. Spore had poor resistance against terrestrial environmental conditions and less nutrient tissues. They could not cope up with the high temperature because of which most of the spores desiccated and died. Therefore, plants came up with “Seed”. Seeds are more resistant and contain more nutrition for the developing embryo as compared to spores.

A seed is an embryonic plant encased in a defensive external covering. It develops at the end of sexual reproduction in Gymnosperms and Angiosperms. Fundamentally, each seed contains an embryonic plant, endosperm to nourish the embryo, and an outer seed coat to protect the embryo from unfavourable environmental conditions. Based on a number of cotyledons, Hutchinson (1884-1972) classified phylum Angiospermae into two subphylum Monocotyledones and Dicotyledones (Singh, 2016). Under favourable conditions of light, temperature, water and oxygen seed germinate to give rise to a plant. These factors act as a stimulus for a seed to germinate. However, after a definite period these factors also do not induce germination. That period is ‘Period of Viability’ for a seed. Based on the seeds viability for germination under storage condition they are classified into three categories i.e. orthodox, intermediate and recalcitrant (Kew, 2017). Recalcitrant seeds remain viable only for a short duration. Therefore, these seeds cannot be stored for a longer period. Intermediate seeds have a moderate period of rest. Orthodox seeds have a long period of rest. These seeds germinate under favourable conditions only, after spending some time in rest. This ‘period of rest’ may vary from days, months to years. This phenomenon exhibited by seed is termed “seed dormancy”.

The primary cause behind dormancy is impermeable seed coat. Seed coat prevents the entry of water, oxygen, temperature and light inside seed. Other than this, immature embryo, after ripening and germination inhibitors too cause seed dormancy (Bewley et al., 2012). In natural conditions, this helps seeds to surpass the unfavourable condition and maintain its viability for a longer period. Which is good thing if we want to store a plant in the form of its seeds but it becomes a problem at the time of propagation because one have to wait until the period of dormancy ends.

So, seed dormancy, which seems to an advantage for the plant has turned to be a problem for humans. As farmers, we want seeds to germinate as soon as possible so that we can get early crops. To get a better understanding of seed dormancy Marianna G. Nikolaev classified seed dormancy into two categories based on morphological and physiological properties of the seed (Nikolaev, 1967). Later on, C. Baskin and J. Baskin have proposed a broad classification system (

Table 1) which includes five classes of seed dormancy (Baskin and Baskin, 2004).

Table 1 Seed Dormancy Classification System (Baskin and Baskin, 2004)

S. No.	Class	Level
1.	A : Physiological dormancy (PD)	Deep
		Intermediate
		Non-deep
2.	B : Morphological dormancy (MD)
3.	C : Morphophysiological dormancy (MPD)	Non-deep simple
		Intermediate simple
		Deep simple
		Deep simple epicotyl
		Deep simple double
		Non-deep complex
		Intermediate complex
		Deep complex
4.	D : Physical dormancy (PY)
5.	E : Combinational dormancy (PY + PD)

Traditionally, methods like chilling, dry storage/elevated temperature, light, leaching, scarification, exposure to chemicals, exposure to fluctuating condition are being used to break dormancy, either individually or in combination of two or more methods (Bradbeer, 1988). All these methods have limitations and percentage of germination is not satisfactory. Recent researches show electromagnetic field radiation (EMFr) affects plants, specifically seeds. Therefore, it could be a novel tool for breaking seed dormancy in orthodox seeds and promoting seed dormancy in recalcitrant seeds.

A Brief Review of the Work Already Done in The Field:

EMFr is a non-ionizing and non-thermal radiation. It is classified as Extremely Low Frequency (ELF) (30-300 Hz), Voice Frequency (VF) (300-3000 Hz), Very Low Frequency (VLF) (3-30 KHz), Medium Frequency (MF) (0.3-3 MHz), High Frequency (HF) (3-30 MHz), Very High Frequency (VHF) (3-300 MHz), Ultra High Frequency (UHF) (300-3000 MHz), Super High Frequency (SHF) (3-30 GHz), Extremely High Frequency (EHF) (30-300 GHz) (Bianchi and Meloni, 2007) (Figure 1). SHF and EHF are microwaves. While transmission EMF is not restricted to their target only, but causes vibration in the medium all along the whole path of transmission. This generates a type of radiation, which is electromagnetic field radiation (EMFr). The major sources of EMFr on outdoors are mobile phone base transceiver stations (BTS), TV Towers (TT), Radio Towers (RT), and high voltage electrical transmission lines (HVETL) (Siegrist et al., 2005). EMFr although a non-ionizing radiation, so it can not cause physical disruption upon impact with matter, but may, in some situations, cause some types of biological effects (Pietruszewski et al., 2007).

Figure 1 Different Electromagnetic Frequencies Range (in Hz)

Plants have various light absorbing molecules that empower them to react to changing light in the environment. Light signals consequently control many procedures, for example, pigment synthesis, seed germination, and stem elongation, leaf and flower development. As light is also a form of EMFr (in THz range). Therefore, plants are always under the exposure of EMFr.

Plants serve as a better model organism than an animal because of their immobility, their sensitivity to even minute changes in their environment and their lack of a psychological stress response. Along with this, plants have more surface/Volume ratio (SVR) as compared to animals. This confirms that plants have a high proportion of cells which directly interact with the EMF (Vian et al., 2007). Even though they have evolved their own way of circumventing and mitigating the harmful effects of radiation. However, with the increasing anthropogenic intervention, the surrounding is changing at a very fast pace and evolution does not happen with that pace. As EMFr can penetrate through the cell wall, so it can cause effects not only at molecular and cellular level but also even at genetic level. This reflects in the growth, development, physiology and biochemical process in a plant's body and more on its life expectancy and productivity. Plants are the only producers on Earth hence, it becomes essential for us to study the effect of growing EMFr on them, specifically on seeds as life of a plant starts with a seed.

SEEDS:

Four studies in seven plant species have been cited which are inconclusive. They have used EMF ranging from MHz to GHz range for a duration of 10 min. to 2h. Firstly, Parsi (2007) in his Ph.D. work while working on soybean concluded that with the increase in the number of seeds per batch, the percent increase in germination decreased irrespective of duration of exposure (Parsi, 2007). Secondly, Tkalec et al (2009) observed no significant differences in the germination rate in Allium cepa L. (Tkalec et al., 2009). Thirdly, Radzevicinus et al (2013) after a three yearlong study on Daucus sativus, Lycopersicon esculentum and Raphanus sativus observed inconsistent behaviour in germination rate, germination energy, hypocotyl height and hypocotyl thickness (Radzevičius et al., 2013). Lastly, Ungureanu (2009) observed no direct correlation between the intensity of induction and the effects caused by the different magnetic induction in Hippophae rhamnoides L. seed germination (Ungureanu et al., 2009).

A few studies have also been cited showing negative effects of EMF on seed germination. The exposure duration ranging from seconds to days under Hz, MHz to GHz of EMFr. The effect of low frequency EMF have significantly reduced seed germination as evident by decrease in water absorption rate in Mung beans (Huang and Wang, 2008), decrease in germination percentage in Plantago media L. (Shashurin et al., 2014) and decrease in hydration and dry mass loss in winter wheat (Sukiasyan et al., 2012). Similarly, high frequency EMF have also reduced seed germination. Assimilating area was reduced in case of Daucus sativus and Raphanus Sativus (Radzevičius et al., 2013). 2.5 GHz have proved lethal to the seeds of Cucumis myriocarpus (Brodie et al., 2012). Mean germination time of Oryza sativa L. decreased with the increase in exposure time (Talei et al., 2013). Glycine max exposed to 900 MHz for 4 h to higher amplitude (41V/m) GSM radiation resulted in diminished outgrowth of the epicotyl. The exposure to lower amplitude (5.7 V/m) GSM radiation did not influence outgrowth of epicotyl, hypocotyls, or roots. The exposure to higher amplitude continuous wave (CW) radiation resulted in reduced outgrowth of the roots whereas lower CW exposure resulted in a reduced outgrowth of the hypocotyl. The growth of epicotyl and hypocotyl was found to be reduced 2 days after 5 days of extremely low level radiation (GSM 900 MHz, 0.56 V/m) exposure to the seedlings (Halgamuge et al., 2015).

Interestingly, in sixteen species under ten studies indicated positive effects of EMF on seed germination after giving exposure to EMF ranging from Hz, MHz and GHz to a duration from minutes to weeks. Five out of ten studies supports positive effect of ELF on seed germination. The water uptake rate in Mung beans seeds under 20 and 60 Hz exposure is higher than the control beans (Huang and Wang, 2008). Twenty days under 10 Hz for 5 h per day accelerated the rate of germination and enhanced the Glycine max L. seed viability (Radhakrishnan and Ranjitha Kumari, 2012). Urtica dioica L. observed highest rate of dry seed germination percentage after 5 min and 10 min exposure to 1.6 mT of field. For 20 minutes, a field of 1.6 mT had lower germination percentage than a field of 0.8 mT. 0.8 mT for 5 min caused most of the germination in wet seeds. The samples treated in the field of 0.8mT for 20 min had the least germination percentage (Rostami Zadeh et al., 2014). Similarly, 16Hz of EMF for 2 h increases the ground germination rate by 17.6% on average in sugar beet (Rochalska, 2008). Significant increase in germination percentage, emergence index, emergence percentage is also observed in Allium cepa L. exposed to 60 Hz for 15 and 20 min (De Souza et al., 2014). Exposing the Oryza sativa L. seeds to microwave frequency for ten hours improved the germination rate. 10 h microwave frequency was the most effective exposure time to germinate the seeds, so that 66.7% of the seeds germinated after 2 days, and this percentage increased up to 100% after 3 days. The other exposure times of microwave frequency demonstrated varying effects as reflected by germination percentage values ranging from 93 to 98% (Talei et al., 2013). In a field study on Zea mays L. grains cultivated 6 m away from the cellular phone station, recorded a higher germination percentage after 4 and 6 days (50 and 80%, respectively) from sowing than that of the control (30 and 60%, respectively) and that of the grains at other distances. While after 8 days from sowing the germination recorded 100% for all distances (Khalafallah and Sallam, 2009). Glycine max seedlings exposed for 5 days to an extremely low level of radiation (GSM 900 MHz, 0.56 V/m) and outgrowth studied 2 days later. The outgrowth of roots was promoted (Halgamuge et al., 2015). In an indigenous broad study considering four plant species, viz. Triticum aestivum, Cicer arietinum, Vigna radiate and Vigna Aconitifolia under microwave frequency showed up to 60% improvement in germination. Seed germination seems to improve even at lower frequencies also (Ragha et al., 2011). Another broad study endorsing the positive effect of microwave frequency includes three plant species. In Daucus sativus hypocotyl thickness tripled with better germination energy, in Lycopersicon esculentum assimilating area significantly increased and in Raphanus sativus germination rate, germination energy, hypocotyl thickness showed significant enhancement (Radzevičius et al., 2013).

Although evidences are available, which support negative effects of EMFr on seed germination inconclusive and positive effects of EMFr encourage us to explore more.

RESULT:

Sixteen papers from 14 countries have been compiled. The majority of the work is from Australia, India, Taiwan and Croatia. Taking into account the number of publication in the past 10 years, there is a slow progress in this field. More than 70% researchers cited deals either with Extremely Low Frequency (ELF) or with Ultra High Frequency (UHF). Rest others focused on Very High Frequency (VHF) or Super High Frequency (SHF). In terms of plant material, 17 plant species from 11 families have been investigated, out of which three top species are Daucus sativus, Glycine max and Raphanus sativus (Figure 2). Out of 11 families, only Poaceae and Amaryllidaceae are from subphylum Monocotyledones. Hippophae rhamnoides L. is the only shrub studied rest all are herbs. Except Beta vulgaris all seeds have germination percentage more than 75%. Primarily seeds having physical and physiological dormancy are vastly studied. All seeds studied are orthodox. Conclusion of three papers are inconclusive, seven negative and ten studies suggest positive effect.

Figure 2 Frequently used plant material

CONCLUSION:

Plants constitute an outstanding model to study such interactions since their architecture (high surface area to volume ratio) optimizes their interaction with the environment. Nonionizing electromagnetic fields radiation (EMFr) that are increasingly present in the environment constitute a genuine environmental stimulus able to evoke specific responses in plants which is very much similar with those observed after a stressful treatment. Hence, Balmori (2010) considered nonionizing EMFr is being a new ‘‘poison’’ with a slow effect on nature (Balmori, 2010). However, according to Vian (2016) it is too early to say that. He described EMFr as a non-injurious, genuine environmental factor that readily evokes changes in plant metabolism (Vian et al., 2016). If we can establish the positive effect of EMFr on plants than we may consider the use of plants or other vegetation to ameliorate the effects of high-voltage parallel lines adjacent to human activity. Specifically, recommended growing plants in public places, around residential blocks, and on the roof of the residential building.

The overall summary of the papers reviewed so far neither approve nor disapprove the harmful effects of EMFr on plants. In fact, inconclusive studies along with positive studies encourages for additional investigations. Verschaeve (2014) suggested that future studies in this field should be as rigorous as possible, detailing a complete description of correct experimental conditions and dosimetry (Verschaeve, 2014). As some studies suggested an improvement in seed germination after EMFr exposure, it can be exploited in agriculture as well as in horticulture. We can use EMFr on recalcitrant seeds also to improve their storage behaviour.

REFERENCES:

1. Balmori, A. (2010). The incidence of electromagnetic pollution on wild mammals: A new “poison” with a slow effect on nature? The Environmentalist, 30(1), 90-97. doi: 10.1007/s10669-009-9248-y

2. BBaskin, J. M., and Baskin, C. C. (2004). A classification system for seed dormancy. Seed Science Research, 14(01), 1-16.

3. Bewley, J. D., Bradford, K., Hilhorst, H., and nonogaki, h. (2012). Seeds: Physiology of Development, Germination and Dormancy, 3rd Edition: Springer New York.

4. Bianchi, C., and Meloni, A. (2007). Natural and man-made terrestrial electromagnetic noise: an outlook. Annals of Geophysics, 50(3), 435-445.

5. Bradbeer, J. (1988). Seed dormancy and germination.

6. Brodie, G., Ryan, C., and Lancaster, C. (2012). The Effect of Microwave Radiation on Prickly Paddy Melon (Cucumis myriocarpus). International Journal of Agronomy, 10. doi: 10.1155/2012/287608

7. De Souza, A., García, D., Sueiro, L., and Gilart, F. (2014). Improvement of the seed germination, growth and yield of onion plants by extremely low frequency non-uniform magnetic fields. Scientia Horticulturae, 176, 63-69.

8. Halgamuge, M. N., Yak, S. K., and Eberhardt, J. L. (2015). Reduced growth of soybean seedlings after exposure to weak microwave radiation from GSM 900 mobile phone and base station. Bioelectromagnetics, 36(2), 87-95. doi: 10.1002/BEM.21890

9. Huang, H.-H., and Wang, S.-R. (2008). The effects of inverter magnetic fields on early seed germination of mung beans. Bioelectromagnetics, 29, 649-657.

10. Kew, R. B. G. (2017). Seed Information Database (SID). Version 7.1. http://data.kew.org/sid/

11. Khalafallah, A., and Sallam, S. M. (2009). Response of maize seedlings to microwaves at 945 MHz. Romanian J. Biophys, 19(1), 49-62.

12. Nikolaev, M. G. (1967). Physiology of deep dormancy: Наука [Ленинградское отд-ние].

13. Parsi, N. (2007). Electromagnetic effects on soybeans. (Master of Science), University of Missouri, Columbia.

14. Pietruszewski, S., Muszynski, S., and Dziwulska, A. (2007). Electromagnetic fields and electromagnetic radiation as non-invasive external stimulants for seeds (selected methods and responses). International Agrophysics, 21(1), 95-100.

15. Radhakrishnan, R., and Ranjitha Kumari, D. B. (2012). Pulsed magnetic field: a contemporary approach offers to enhance plant growth and yield of soybean. Plant Physiology and Biochemistry, 51, 139-144. doi: 10.1016/j.plaphy.2011.10.017

16. Radzevičius, A., Sakalauskienė, S., Dagys, M., Simniškis, R., Karklelienė, R., Bobinas, Č., and Duchovskis, P. (2013). The effect of strong microwave electric field radiation on:(1) vegetable seed germination and seedling growth rate. Zemdirbyste-Agri, 100, 179-184.

17. Ragha, L., Mishra, S., Ramachandran, V., and Bhatia, M. S. (2011). Effects of low-power microwave fields on seed germination and growth rate. Journal of Electromagnetic Analysis and Applications, 165-171.

18. Rochalska, M. (2008). The influence of low frequency magnetic field upon cultivable plant physiology. Nukleonika, 53, 17-20.

19. Shashurin, M. M., Prokopiev, I. A., Shein, A. A., Filippova, G. V., and Zhuravskaya, A. N. (2014). Physiological responses of Plantago media to electromagnetic field of power-line frequency (50 Hz). Russian Journal of Plant Physiology, 61(4), 484-488. doi: 10.1134/S1021443714040177

20. Siegrist, M., Earle, T. C., Gutscher, H., and Keller, C. (2005). Perception of mobile phone and base station risks. Risk Analysis, 25(5), 1253-1264.

21. Singh, G. (2016). Plant Systematics, 3/ed.: An Integrated Approach: CRC Press.

22. Sukiasyan, A., Mikaelyan, Y., and Ayrapetyan, S. (2012). Comparative study of non-ionizing and ionizing radiation effect on hydration of winter wheat seeds in metabolic active and inactive states. The Environmentalist, 32(2), 188-192. doi: 10.1007/s10669-012-9392-7

23. Talei, D., Valdiani, A., Maziah, M., and Mohsenkhah, M. (2013). Germination response of MR 219 rice variety to different exposure times and periods of 2450 MHz microwave frequency. The Scientific World Journal, 2013, 408026-408026. doi: 10.1155/2013/408026

24. Tkalec, M., Malarić, K., Pavlica, M., Pevalek-Kozlina, B., and Vidaković-Cifrek, Ž. (2009). Effects of radiofrequency electromagnetic fields on seed germination and root meristematic cells of Allium cepa L. Mutation Research-genetic Toxicology and Environmental Mutagenesis, 672(2), 76-81. doi: 10.1016/j.mrgentox.2008.09.022

25. Ungureanu, E., Maniu, C. L., Vântu, s., and Cretescu, I. (2009). Consideration on the peroxidase activity during Hippophae rhamnoides seeds germination exposed to radiofrequency electromagnetic field influence. Analele Stiintifice ale Universitatii "Alexandru Ioan Cuza" din Iasi Sec. II a. Genetica si Biologie Moleculara, 10(2), 29-34.

26. Verschaeve. (2014). Environmental Impact of Radiofrequency Fields from Mobile Phone Base Stations. Critical Reviews in Environmental Science and Technology, 44(12), 1313-1369. doi: 10.1080/10643389.2013.781935

27. Vian, A., Davies, E., Gendraud, M., and Bonnet, P. (2016). Plant Responses to High Frequency Electromagnetic Fields. Biomed Res Int, 2016, 13. doi: 10.1155/2016/1830262

28. Vgian, A., Faure, C., Girard, S., Davies, E., Hallé, F., Bonnet, P., Paladian, F. (2007). Plants Respond to GSM-Like Radiation. Plant Signaling and Behavior, 2(6), 522-524.

Received on 20.12.2022 Modified on 24.01.2023

Res. J. Pharmacognosy and Phytochem. 2023; 15(1):82-86.

DOI: 10.52711/0975-4385.2023.00012