Causal theory on acceleration of seed germination in the vicinity of high voltage direct current transmission line

https://doi.org/10.1016/j.jtbi.2021.110899Get rights and content

Highlights

  • Seed germination is known to be influenced by electric/magnetic field.

  • The paper provides a theoretical framework for the same.

  • This allows a causal explanation for the effect of HVDC lines.

  • The current variation due to effect of electrical loading has been discussed too.

  • Thus, this work opens new avenues of research in this field.

Abstract

Seed germination is the primary stage of growth in a seed. A wealth of experiments exist in literature to support the existence of correlation between seed germination to the electric and magnetic fields. This becomes more important as researchers have suggested to develop technologies to build ecologically clean and environment-friendly solutions to agricultural practices. Although the literature supports the existence of seed germination acceleration, the lack of a definite causal theory has been observed by numerous researchers over decades. After considering all the existing experimental data, we have formulated a causal theory to explain the factors influencing seed germination around high voltage DC transmission lines. This work opens new avenues of research in this field.

Introduction

Seed germination, by definition, is the sequence of events that commences with water intake and ends with the emergence of the embryonic axis. The visible sign of germination is penetration of seed structure by the radicle surrounding the embryo. Even under optimum conditions, all seeds do not germinate, so successful germination is a major seed quality indicator to get a healthy plant. Food security is currently an alarming issue around the world which becomes especially important in places with unfavorable environment or during times of pandemic (Takaki et al., 2019). By adopting new technologies, germination rate can be improved. This leads to reduced duration of seeding-to-germination and subsequently an overall enhancement of agricultural yield (Shashikanthalu et al., 2020).

Most current methods for increasing yield include the use of chemicals, but substituting them with appropriate physical treatments, viz., magnetic field, gamma irradiation, electric field, laser irradiation, sound, healing energy, light and heat, is a fascinating prospect (Govindaraj et al., 2017). Rifna et al. (2019) reviewed the effects of ultrasound, high pressure processing, magnetic field, microwave radiation, pulsed electric field, ultraviolet, electrolyzed oxidizing water, plasma activated water, and non-thermal plasma on germination and growth of different seed varieties. Both enhancement and inhibition can be observed such as with cyclohexane plasma (Dhayal et al., 2006). The seed germination, seedling growth, presence of antioxidant enzymes, lipid peroxidation levels and osmotic adjustment are generally improved (Ling et al., 2015).

To improve the crop quality, processing of seeds can be done using electric field treatment before planting, which is an ecologically clean method than using chemicals. Exposure to high-intensity electric field is found to be effective than chemical agents (Pozeliene, 2001). The magnetic and electric fields may give a viable non-chemical option in agriculture while also protecting the environment and ensuring the safety of the applicator. For reforestation in mountain areas, tree seeds are treated with electric field and then planted by airplane-sowing (Gui et al., 2013). Increasing the growth of medicinal plants like bitter gourd (Momordica charantia) by treating it with electric/magnetic fields can benefit in curing diabetes and other diseases (Mahajan and Pandey, 2015). Balouchi and Sanavy (2009) reported that during the treatment, seed lots of annual medics (usually found contaminated by dodder) with electromagnetic fields has resulted in total germination and emergence of medics whereas germination of dodder was decreased. In arid areas, even spring season is unfavorable for seed germination. Thus, the development of electrical technologies become a simple, reliable, economical and environmental friendly solution. Such analysis on the influence of electric and magnetic field is also necessary for far ahead objectives like plantation on Moon and Mars (Karoliussen et al., 2013). Following is a brief discussion on the treatments used in literature.

Pulsed electric field treatment on Iranian alfalfa seeds showed increased germination rate (Rezaei-Zarchi et al., 2012), increased phenolic compound in buckwheat seed (Nam et al., 2018), enhanced germination rate in barley seeds after treating with 180 pulses in 60 s (Chen et al., 2019), and improved germination efficiency and bioactivity profile of chick pea, broad beans, lentils (Vasilean et al., 2018). Magnetic field treatment of sunflower seeds showed increased germination rate by 5–11% compared to control (Vashisth and Nagarajan, 2010), improved germination characteristics in radish seeds after treating with 0.02 T for 720 s (Konefał-Janocha et al., 2018), and increased germination by 14% compared to control after treating with 0.005 T for 360 s (Izmailov et al., 2018). Efficiency of treatments is known to be dependent on the kind of electrode configuration used, such as the most common plate-to-plate (Ohshima et al., 1997, Isobe et al., 1999), needle-to-plate (Ohshima et al., 1997, Sato et al., 2001), ring-to-cylinder (Ishida et al., 2003), or spiral winding (Ohshima et al., 1997, Ishida et al., 2004). The concentrated area of the field is shown to be strongly influenced by electrode shape (Sato et al., 2001). Researchers keep on experimenting and develop more sophisticated treatment systems, for instance, Kitajima et al. (2007) reported a textile electrode (combination of polyester fibre and 0.2 mm diameter tungsten wires).

Ultrasound treatment on green pea seeds showed that germination percentage of nontreated seeds ranging between 81.39% and 85.01% while germination percentage of decontaminated seeds ranged between 76.64% and 98.18% (Chiu and Sung, 2013), sunflower seeds showed germination rate 95% compared to 68% in control (Machikowa et al., 2013), and improved germination rate in red rice and brown rice after exposure to 25 kHz for 5 min (Ding et al., 2018). Microwave radiation treatment on potatoes resulted in more actively sprouted eyes (Jakubowski, 2016), good germination and vigor index in barley seeds after exposure to microwave power of 400 W for 20 s (Cretescu et al., 2013), enhanced growth index after exposure of 9.3 GHz on tomato seeds (Kumari et al., 2018), positive impact on garden cress after exposure to 2.4 GHz for 5–15 s (Tomasz, 2018), and microwave treated water improved growth rate of corn and pepper seedling compared to tap water (Alattar et al., 2018). Non-thermal plasma treatment of rapeseed seed increased germination by 7.7% (Puligundla et al., 2017), germination percentage of rice seeds increased from 90% to 98% (Khamsen et al., 2016), germination in soybean increased from 68% to around 100% (Ling et al., 2014), increased water uptake and 5% increased germination rate in mulungu seeds (Junior et al., 2016), cold plasma (80 W/cm3) inhibited native pathogens with enhanced growth in maize seed (Zahoranová et al., 2018), and increased water absorption along with enhanced germination in spinach (Ji et al., 2018).

Embryonic cells in seeds have cell walls which to some extent protect cells from abiotic stresses and that the seed surface coat also acts as a protective barrier. Li et al. (2017) studied the morphology of wheat seed coat. The altered morphology depends on the treatment used and initial seed coat morphology. A close inspection of seat coat also reveals surface hydrophilization. Researchers have observed the etching effect on the seed coat using methods like scanning electron microscopy (Meng et al., 2017, Rahman et al., 2018, Stolárik et al., 2015, Bafoil et al., 2019, Park et al., 2018, Guo et al., 2017, Adhikari et al., 2020). Gómez-Ramírez et al. (2017) examined the surface of quinoa seeds with X-ray photoelectron spectroscopy and revealed that exposure of seeds induced an increase in the oxygen and nitrogen content of the seed surface at the expense of carbon. After exposure of the seeds to water, the potassium and nitrogen species diffused into the interior of the seed which in turn promotes seed germination in a similar way the exposure to nitrate-rich water influences seed metabolism and water uptake (Gómez-Ramírez et al., 2017, Starič et al., 2020). It is understood that the wetting properties of organic surfaces are correlated with the amount of oxygen-containing functional groups at the sample surface (Occhiello et al., 1991, France and Short, 1998). The change in water contact angle is attributed to chemical occurrences on the seed surface during treatment which turn the normally hydrophobic seed coat to a hydrophilic one (Ji et al., 2018). Numerous experiments showed a decrease in the water contact angle of the seed surface (Kurek et al., 2019, Los et al., 2018, Zahoranová et al., 2018). This lead to modification in the wetting properties of the surfaces of seeds as examined by Bormashenko et al. (2012). Thus, improvement in germination properties like water uptake, seed reserve utilisation, soluble protein and sugar content can be observed (Randeniya and de Groot, 2015).

Most of the literature available so far consists of experiments followed by statistical study of germination percentage, velocity coefficient, response time, probit analysis, curve-fitting of cumulative germination, logistic regression, proportional hazards regression and accelerated failure time analysis. Scott et al. (1984) summarized such methods and examined their strengths and weaknesses. Experimentation and subsequent statistical analysis of variance or regression methods are appropriate when germination of all viable seeds is observed, but they are not suitable if some viable seeds fail to germinate. Such missing (censored) data complicates statistical analysis and subsequent interpretation, therefore, encouraging careful designing of germination tests. Seed germination analytics should not only involve individual qualitative responses, but also population responses distributed over time.

In recent decades, electric and magnetic fields have gained considerable importance since experimentation and observations support the fact that these fields cause physiological and biochemical changes in seeds (Gemc et al., 2013). Like every living being, plants too are constantly surrounded by electromagnetic fields (from electrical machinery, transmission lines, electrical wiring, etc.) which is the focus of this work. To investigate the effect of high electric field, tomato seeds were placed in 50 Hz electric field (10 to 30 kV/cm) which showed improvement in germination (Patwardhan and Gandhare, 2013). Iwata et al. (2011) exposed thale cress to 60 Hz AC electric field of 2.5 kV/m which accelerated seed germination, but this was not significant enough in comparison to DC field. Gandhare and Patwardhan (2014) treated tomato seeds with three different approaches: electrostatic field, microwave and corona discharge. They found that application of electrostatic field was simple and powerful at the optimal dosage of 20 kV/cm (for 20 s). The positive influence of DC electric field was also demonstrated by improvement in the seed germination rate and seedling stem length of Raphanus sativus longipinnatus (Okumura et al., 2010, Okumura et al., 2012) and Arabidopsis thaliana (Okumura et al., 2014). Due to promising results with DC field, the focus of this paper will be to investigate the causal explanation of influence(s) of high voltage direct current (HVDC) on the seeds near a transmission line.

In order to increase the accessibility of electricity to everyone, several transmission poles have been erected and power lines being rapidly setup. Most of these pass through farms, thus, researchers are curious about their influences. Soja et al. (2003) experimented with wheat and corn under the influence of electric and magnetic field strengths from 0.2 to 4 kV/m and 0.4 to 4.5 μT respectively at four distances (40 m, 14 m, 8 m, and 2 m) from a 380 kV transmission line. They reported that wheat grain yields were 7% higher in the plots with the lowest field exposure, but no significant yield difference for corn yields was seen. The proximity effects of high voltage electric power transmission lines on the growth of plants Leyland Cypress and Japanese Privet were examined in a private nursery located in Sakarya, Turkey (Demir, 2010). At north Jeddah city, Alaish and Al-Zahrani (2014) conducted a field study to evaluate the changes in wild plants around electricity towers where plant morphology, physiological activity and metabolic parameters were observed. A recent survey by Barman and Bhattacharya (2015) on the impact of high voltage transmission lines explored the growth characteristics of Brassica juncea and Saccharum officinarum under field conditions of 132 kV and 400 kV power lines at Kamalpur and near Plassey monument respectively, both located in West Bengal, India.

However, the combined discussion of above along with the concentric magnetic field produced by the current carrying powerlines mostly seems to be ignored in the literature, which needs due attention. The effect of magnetism on plant development is very well captured by several experiments (Payez et al., 2013). Germination acceleration in wheat and bean seeds have been observed under various magnetic fields and osmotic pressures (Pietruszewski and Kania, 2010). The impact of magnetic field, magnetically treated water and a combination of both on the seed germination in sunflower plants has been studied by Matwijczuk et al. (2012). Negative impact was found in the case of magnetically treated water, short duration of magnetism activity, and connection with low-flow times. Anand et al. (2012) exposed the maize grains to 200 mT and 100 mT for 1-2 h to find improvement in all growth parameters. A similar hike was observed in the germination of cucumber seeds (Bhardwaj et al., 2012). Strikingly, germination and growth increased positively for bean and wheat seed in presence of static magnetic field, along with increasing osmotic pressure or salt stress compared to their respective controls (Cakmak et al., 2010).

Studies conducted to analyze the influence of magnetic fields in laboratory experiments are considered as base for the direction towards our research problem. Despite the consistent observation that electric/magnetic fields influence the growth of seedlings, it is not appropriate to simply extrapolate the established understanding to all settings. This poses the requirement of a fundamental theory because the effects observed in a particular scenario alter with several factors at play. For instance, seeds underneath powerlines are constantly exposed, whereas the literature mostly considers finite exposure times of few minutes to few hours (Hulevskyi et al., 2019). The lack of proper understanding of the underlying biophysical mechanism has been emphasized repeatedly over years (Costanzo, 2008, Payez et al., 2013, Su et al., 2015, Dannehl, 2018).

Hence, the problem instigated our curiosity and is considered in this paper. This work, thus, conducts a thorough investigation of the causal influences to develop a theory to quantify the effect of electric and magnetic fields emanated by the HVDC transmission line on the seeds in its proximity.

Section snippets

Identification of factors and development of theory

In a germinating seed, the rate of CO2 production has a polarity-dependent electrostatic influence (Sidaway, 1966). In the early growth stages of seed, nitric oxide (NO) and the oxidization-reduction potential inside the seed cells are more positively involved by applying electric field (Su et al., 2015). Ozone generation by partial discharges between seed seems to be a main sterilizing agent, while the activation of OH radicals under the action of the high-intensity electric field explains the

Salient discussion and deliberation over effect of loading

It is clear from the equations that different seeds will respond differently due to different dielectric constant (κ). Moreover, this response is further affected due to change in κ because of changing composition of the seed with water intake and other processes. This creates a cyclic relationship between electric and magnetic influences. In addition to direct promotional effects, let us look at the other aspects as well. During experimentation, Moon and Chung (2000) observed an inhibitory

Conclusion and future scope

While there is ample evidence that electric and magnetic fields affect seed germination, researchers have constantly highlighted the absence of a theoretical paradigm that could explain experimental results. The seeds in the proximity of transmission lines are under direct exposure of electric/magnetic fields emanated by it. This makes us curious to investigate the underlying interplay of involved factors. The exact relations for the effect of electric and magnetic fields are derived in terms

CRediT authorship contribution statement

Abhimanyu Kumar: Conceptualization, Formal analysis, Investigation, Writing - original draft, Visualization. Om Prakash Pandey: Resources, Writing - review & editing, Visualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors thank the anonymous reviewers for their constructive comments and suggesting necessary corrections which allowed improvement of this manuscript.

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