Modern scientific and technological research results show that various life activities in the biological world are accompanied by electromagnetic phenomena. At present, bio-magnetic technology has attracted more and more attention and research interest from professionals and has been widely used in the fields of medicine, agriculture, horticulture, environmental protection and bioengineering (Özdinç and Yalçin, 2018). In medical science, magnetism has long been popularised to the stage of specific applications and has become an important medical detection method. In agricultural and horticultural areas, magnetic field (MF) effects on crops are being extensively explored.
Seeds/plants chemical treatments, including fertilisers, pesticides and fungicides, bio-stimulants, and so on, are widely used in agricultural and horticultural production. They effectively ensure the crop emergence rate, uniformity of emergence, plant growth rate in the following development stages and crop yield. However, chemical treatment has been controversial from the perspective of environment protection and food safety. More and more chemical reagents are deprecated or prohibited from being used. Under the general trend of environment-friendly agricultural and horticultural production, as an alternative to chemical treatment, physical treatments, such as MF, electric fields, microwave, and lasers, have attracted more and more attention (Aladjadjiyan, 2007; Chen et al., 2016).
Applying magnetic physical treatment in agricultural and horticultural production has always been a keenly observed method by agricultural and horticultural researchers. The use of artificial MF to treat cultivated crop seeds/plants improves their agronomical characteristics, promotes seed germination and vigour, increases yield, improves crop quality and enhances stress tolerance (Shine et al., 2011; Bhardwaj et al., 2012; Da Silva and Dobránszki, 2016; Kataria et al., 2017; Bahadir et al., 2018; Hozayn et al., 2018; Krawiec et al., 2018; Radhakrishnan, 2018; Anand et al., 2019; Baghel et al., 2019; Hozayn et al., 2019; Kataria et al., 2019; Liu et al., 2019; Menegatti et al., 2019; Alvarez et al., 2020; Kataria et al., 2020; Souza-Torres et al., 2020; Adetunji et al., 2021; Bukhari et al., 2021; Harb et al., 2021; Samarrai et al., 2022). This technology has the advantages of less physiological damage, low cost and easy operation and application. Moreover, it produces no pollution and has a high input–output ratio (Michalak et al., 2019; Nyakane et al., 2019; Abdel Latef et al., 2020; Johnson and Puthur, 2021; Pagano et al., 2023).
Although the main focus of MF application research is in the area of crop commercial trait improvement, still in recent years, more and more researchers have turned their attention to the application of MF treatment in the field of plant stress tolerance improvement. Both magnetopriming and magnetised water (MW) irrigation can enhance the tolerance and vitality of cultivated plants under various environmental stresses (Baghel et al., 2019; Hasan et al., 2020; Hozayn et al., 2021; Kataria et al., 2022, 2023). It ensures not only the ability of plants to survive under adverse stress conditions, but also the accumulation of heavy metals by plants grown in heavy metal soil; thus, it improves the ability of plants to help in soil restoration (Tang et al., 2022; Prajapati and Patel, 2023). MF treatment research in this direction provides great potential for the use of plants for heavy metal soil remediation.
At present, there are many reports in the area of magnetic effects on plants. The research not only involves the positive effects after treatment, but also provides some discussion about its mechanisms. However, there are also reports on some cases when application of MF on seeds was not successful or repeatable. For some crops, only in certain range(s) of the MF intensity and exposure time have caused the positive effects (Araújo et al., 2016; Farooq et al., 2019; Rifina et al., 2019; Sarraf et al., 2020;), while the other ranges have given weakened or even negative effects (Abdani Nasiri et al., 2018; Nair et al., 2018; Florez et al., 2019; Khaledi et al., 2019; Massah et al., 2019; Migahid et al., 2019; Júnior et al., 2020; Afzal et al., 2021). Due to the complexity of the interaction between the used MF and plants, the research of the mechanism is still in the exploration stage and needs further study (Radhakrishnan, 2019). Therefore, an in-depth study of the macroscopic regularity and mechanism of the regulation of plant physiological activities by magnetic treatment is still an area that needs to be vigorously developed. Meanwhile, the progress in MF treatment research will help reduce the use of traditional chemical reagents in agricultural and horticultural activity. Thus, the method has broad prospects in the development of environment-friendly agricultural and horticultural production and providing food-safety assurance.
The main aim of this review was to firstly highlight research findings with relevance to seeds or/and plants growing under the influence of a constant or alternating MF and MW and the impact on seed germination, plant growth, yield and their quality in horticultural and agricultural crops, enzyme activity, stress tolerance, and genome stability. Secondly, it was done to elucidate the molecular mechanism regarding the MF interaction based on the existing published results.
As magnetism becomes more and more widely used in agriculture and horticulture, we believe that it becomes necessary to summarise the latest and most-important scientific research results in the related fields and the results of further in-depth research on its mechanism. This could serve as a guide to relevant scientists and will attract more agricultural researchers to pay attention to this field of plant science. By studying selected papers in English and Chinese, we aimed to gain an understanding of past research results and come out with conclusions and recommendations for both the future MF experiments and its applications.
The English literature cited in this paper was mainly obtained through Google Scholar, whereas the Chinese ones came from the collection of the China National Knowledge Infrastructure (CNKI) platform. The searched keywords were ‘effect of MF and MW on plants’, ‘effect of MF on seeds’ and ‘application of MF and MW in agriculture and horticulture’. The present paper consists of five chapters discussing the points of concern for researchers in related fields. These are: ‘Materials and methods of the use of MF treatment’, ‘Plant parameters enhanced by MF’, ‘Molecular mechanisms understanding the response to MF treatments’, ‘Difficultly in application’ and ‘Conclusions and recommendations’. Afterwards, based on the experimental subjects, methods and results collected from the literature, several sub-chapters were further sub-divided into some chapters. For example, in the chapter ‘Plant parameters enhanced by MF’, five sub-chapters were sub-divided, with a focus on explaining the impact of MF on various aspects of plant’s development. They included ‘Increase of seed germination and seeding growth’, ‘Increase of crop yield and quality’, ‘Enhancement of enzyme activity’, ‘Increase of the tolerance to environmental stress’ and ‘Impact on genomic stability’. In each chapter or sub-chapter, representative experimental results, from the collected papers, were elaborated in detail. Their aim was to provide more specific information for researchers in related fields and to provide an experimental results data foundation for future research and application. The present paper integrated information related to MF with a large amount of data by using a table. Photographs were also used to make the relevant descriptions more concrete and easier for readers to understand. All this allowed us to make final conclusions and recommendations.
The MF processing technical parameters, for different methods of using, mainly include: MF intensity, exposure time, frequency of change (for alternating MF), and the number of cutting magnetic lines (for MW). So far, the MF treatment of cultivated crops can be roughly divided into three categories: The first method is to treat seeds/plants directly with MF, depending on the experimental design, the processing time ranges from tens of minutes to several days (Hołubowicz et al., 2014; Hozayn et al., 2018; Baghel et al., 2019; Farooq et al., 2019; Jin et al., 2019; Menegatti et al., 2019; Radhakrishnan, 2019; Xia et al., 2020; Bukhari et al., 2021; Himoud et al., 2022). The types of MF that can be used include static MF or varying MF. Static MF is mostly provided by permanent magnets made of alloys such as iron, cobalt and nickel, and it obtains a wide magnetic induction. The varying MF can be obtained according to the MF principle – the alternating current passes through the coil to generate an alternating MF, and the pulsating current passes through coil to generate a pulsating MF. Other types of varying MF are rotating MF, translational MF and gradient MF. Figure 1 shows examples of two devices used in agricultural and horticultural research to generate MF: the Viofor machine which has been patented and previously used in human magnetotherapy (Figure 1, above) and magnets plates (Figure 1, below). The second method is to treat seeds/plants indirectly with MF. In this method, the seeds/plants are not directly treated with the MF generated by a machine or a magnet, but through a medium that is magnetised by MF. The most common way to do so is to treat seeds/plants by MW. MW can be obtained by cutting magnetic lines by water flowing through static MF at a constant flow rate. According to the number of times the water flows through the whole static MF, the treated water can be divided into primary MW, secondary MW and multiple MW. MW can also be obtained by statically placing water directly in MF. The placing time ranges from tens of minutes to tens of hours. Then, the obtained MW is used for seed soaking or plant irrigation (Chibowski and Szcześ, 2018; Abobatta, 2019; Cui et al., 2020; Elhindi et al., 2020; Hasan et al., 2020; Samarah et al., 2021; Kishore et al., 2022; Mohamed et al., 2022). When MW is used for seed soaking, it all depends on the species: their soaking time in MW ranges from several hours to tens of hours. When MW is used for plant irrigation, the treatment covers the whole plant-growing period. An example of an experimental design to study the effects of MW irrigation on plants is shown in Figure 2. However, an already-reported result must be taken into consideration wherein MW would not retain its magnetism after leaving the magnetic source (Zamora et al., 2008). The third method is composite processing. This kind of comprehensive treatment includes: multiple MF/MW processing, composite treatment with both static and alternating MF and composite treatment with both MF and MW (Sarraf et al. 2020).
The research materials include all seeds, seedlings or plants of agricultural, horticultural and other cultivated plants, for example, maize (
According to current reports, the effects of MF treatment on plants are mainly reflected in the following aspects.
Using MF treatment to improve seed germination is still the main direction of current seed MF treatment research. The mechanism of MF treatment to promote seed germination is related to enhancing enzyme activity in seeds, breaking seed dormancy, accelerating seed water absorption, stimulating protein synthesis in seeds and increasing their respiration rate. (Araújo et al., 2016; Radhakrishnan, 2019; Sarraf et al., 2020). A large number of conducted experiments has proven that MF treatment can effectively increase germination parameters of various plants. Positive effects of MF on agricultural and horticultural crops have been reported, for example, on maize (
In the experiment of MF effects on sunflower (
In the area of artificial cultivation of wild medicinal plants, large-scale cultivation is often impossible due to the low seed germination rate. However, it was reported in recent years that the seed germination of
To achieve the improvement of crop yield and quality through MF treatment, two common methods have been reported to be used: direct MF treatment on seeds/ plants or through MW. These two ways can effectively increase crop germination rate (Baghel et al., 2019; Selim et al., 2022), promote root formation (Ehtaiwesh et al., 2019; Joshi-Paneri et al., 2023), result in seedling robustness (Baghel et al., 2019), increase leaf area (Baghel et al., 2019; Ehtaiwesh et al., 2019; Selim, 2019; Hozayn et al., 2021; Himoud et al., 2022) and enhance stress tolerance (Nyakane et al., 2019; Radhakrishnan, 2019; Sarraf et al., 2020). These are important reasons for increasing yield and quality by MF treatment. Moreover, MW treatment/irrigation can accelerate the substance exchange and nutrient absorption between the root surface and the surrounding soil (Samarrai et al., 2022), improve soil quality (Cui et al., 2020) and change the community structure of the organisms (Cui et al., 2020), enhance water quality and reduce its salinity impact (Elhindi et al., 2020; Hassen et al., 2020; Samarrai et al., 2022). This way, they achieve the purpose of improving yield or quality. The relevant reports are mainly concentrated on maize (
In the experiment on mung bean (
MF treatment can lead to the directional alignment of intracellular carbohydrates, lipids, proteins and other polar molecules and metal ions. It has made the conformation change of the enzymes which contain metal ions of Mg, Zn, Mn, Fe, thereby changed the enzymes’ activity (Liu et al., 2003; Han et al., 2008). The study on plants’ enzyme activities changed by MF treatment were mainly focused on peroxidase (POD) (Bao and Yun, 2010; Anand et al., 2019; Kataria et al., 2019; Abdel Latef et al., 2020), catalase (CAT) (Anand et al., 2019; Abdel Latef et al., 2020; Harb et al., 2021) and superoxide dismutase (SOD) (Anand et al., 2019; Kataria et al., 2019; Abdel Latef et al., 2020; Harb et al., 2021). Part of the study was also directed to polyphenol oxidase (PPO) (Abdel Latef et al., 2020), nitrate reductase (NR) (Radhakrishnan, 2019; Kataria et al., 2022, 2023), malate dehydrogenase (MDH) (Júnior et al., 2020), ascorbic acid peroxidase (APX) (Nyakane et al., 2019; Abdel Latef et al., 2020; Harb et al., 2021), glutathione reductase (GR) (Araújo et al., 2016) and other enzymes, and have shown positive feedback.
Plant enzyme activity directly affects various physiological indicators of plants (Nyakane et al., 2019; Radhakrishnan, 2019; Sarraf et al., 2020; Kataria et al., 2022). Therefore, studies on the effects of MF on enzyme activity are usually incorporated in such works. One of the possible mechanisms to get better traits through seeds/plants MF treatment is enzyme activities changes led by MF. They are presented in the next chapter.
Environmental stress increases the production of reactive oxygen species (ROS) in plants, which then leads to their peroxidative damage. Moreover, oxidative damage initiated by ROS is also the main reason leading to the plant’s ageing (Muller et al., 2007; Van Raamsdonk and Hekimi, 2009). POD, CAT and SOD, the main enzymes related to the elimination of ROS in plants, eliminate excessive ROS caused by stress and maintain ROS balance in plants, thereby protecting them from peroxidative damage (Anand et al., 2019; Kataria et al., 2019; Abdel Latef et al., 2020; Harb et al., 2021). MF treatment enhances the plants’ ability to eliminate ROS by increasing the activity of the above-mentioned enzymes, thereby enhancing plant stress tolerance and anti-ageing capabilities (Liu et al., 2003; Han et al., 2008; Nyakane et al., 2019; Radhakrishnan, 2019; Sarraf et al., 2020).
The MF effect on plant tolerance to heavy metal stress can be used in the area of contaminated soil restoration (Prajapati and Patel, 2023). Dissolved organic matter (DOM) in the
The coordination of SOD, POD and CAT can keep free radicals in cells at a relatively low level and enhance the anti-ageing ability of seeds. As the seed ageing time goes by, the activity of above three enzymes in seeds gradually decreases. For the seeds treated with MF, the decreasing trend of these enzymes’ activity was significantly alleviated. There are reports that the anti-ageing ability of pepper (
The impact of magnetic treatments on genome stability was investigated by Hozayn et al. (2015) in onion seeds exposed to MF in a static magnetic device. The mitotic index of meristematic cells increased in response to all the tested conditions. However, a concomitant increase in the frequency of chromosomal aberrations, although not lethal, was also observed (Hozayn et al., 2015). Similar results were reported by Aksoy et al. (2010) in wheat (
A deep understanding of the cellular and molecular pathways triggered upon exposure to MF, responsible for the observed biological reactions, is required to provide improved rationale bases for the design of tailored seed invigoration treatments. The current state of the art highlights multiple pathways and targets, disclosed mainly by studies on animal and human systems (Xu et al., 2021).
An intriguing aspect is related to MF perception that has been suggested to occur according to the ‘radical pair mechanism’ (Hammad et al., 2020). Cryptochromes, highly conserved blue light-absorbing flavoproteins acting as photoreceptors during plant development, have been associated to MF perception in plants, flies, and humans. In the presence of MF, cryptochrome modulates ROS levels and, consequently, the cellular redox reactions. This process, conserved in both plants and animals, affects gene expression (Parmagnani et al., 2022a, 2022b).
In the attempt to explain the impact of MF on biological processes, Binhi and Prato (2017) developed the ‘molecular gyroscope mechanism’ based on the rotation of large fragments of macromolecules or amino acid residues with distributed electric charges in response to MF. The biological effect is related to the reaction yield, the number of gyroscopes that enter this reaction, or those that are in a state of equilibrium. The theoretical model elaborated by Vaezzadeh et al. (2006) is based on the oscillation of ferritin under the influence of MF. A common feature of these models is the hypothesis that the MF energy is absorbed by the cells, affecting the mobility and uptake of ions with important roles in cellular homeostasis.
Information about MF mechanism in plants is still scanty, and the published reports generally focus on the plant response rather than on seed germination. In a recent review, Salentnik et al. (2022) described the effects of MF on plant gene expression, underlining the potential of the technique for applications in the agri-food sector. The few reports, so far contributing to expand the knowledge in plant field, use the model system
Parmagnani et al. (2022b) explored the transcriptomics and metabolomics of ROS production in roots and shoots of
The complexity of the molecular networks underlying the response of plant cells to MF has been so far partially disclosed. The mechanisms of plant perception and signalling and related molecular players still need to be defined as well as the downstream targets (effectors) that contribute to the physiological responses (growth, antioxidant protection). Efforts should be expanded to gain insights into the way the seed pre-germinative metabolism reacts at the molecular level to MF treatments. In this way, it will be possible to design more rationale and controlled MF-based protocols for agri-food applications.
It is important to note that a large number of research results showed that different optimal MF intensities and exposure time for different cultivated crops, cultivars and target traits were found. The excessive intensity and exposure time will lead to weakened positive effects, and even in some crops – to negative effects (Table 1). As in the table below, listed crops, including agricultural, horticultural and herbal plants, all showed positive effects in certain range(s) of the MF intensity and exposure time, while there did exist the adverse dose, which led to negative effects (Table 1). After studying the table, one should be aware that in the past, many researchers who had tried and failed to use MF or MW in their experiments with plants had never reported it. Some of these old experiments could be repeated today when our technical equipment is much better than before. Moreover, many of such reports were published in other-than English languages and, therefore, could have been missed by ones who only follow papers published in English. Another serious difficulty that came from this review is lack of one main way of using MF in practical agriculture and horticulture as it had affected various organs of plants. Therefore, for some species, cultivars and target traits, only by a large number of screening experiments to determine the best treatment conditions, can MF treatment achieve the purpose of effectively improving the target traits of plants.
A summary of positive and negative doses of MF treatment on selected cultivated crops
Crop (genus/cultivar) | Method | Selected parameters | Positive dose | Negative dose | Reference |
---|---|---|---|---|---|
Lentil ( |
Seed MF treatment | Seedling growth, lipid peroxidation and antioxidant enzymes activity | 20 mT, 20 min.; 20 mT, 25 min. | 50 mT, 30 min. | Harb et al. (2021) |
Sunflower ( |
Seed MF treatment | Final emergence rate and mean germination time | 50 mT, 45 min. | 80 mT, 30 min.; 100 mT, 15 min. | Bukhari et al. (2021) |
Seed MF treatment | Seed germination | 125 mT, 24 h; 125 mT, 48 h | 125 mT, 72 h | Bahadir et al. (2018) | |
Soybean ( |
Seed MF treatment | Percentage and speed of germination | 200 mT, 60 min. | 250 mT, 90 min.; 300 mT, 90 min. | Shine et al. (2011) |
Medicinal sage ( |
Seed MF treatment | Radicle length | 15 mT, 5 min. | 3 mT, 5 min.; 30 mT, 5 min. | Abdani Nasiri et al. (2018) |
Radicle dry weight | 15 mT, 5 min.; 30 mT, 5 min. | 3 mT, 5 min. | |||
Sunflower ( |
Seed MF treatment | 1000-achene weight (yield of the plants grown from MF treated seeds) | 100 mT, 10 min. | 150 mT, 10 min. | Afzal et al. (2021) |
Wheat ( |
Seed MW treatment (distilled water) | Seed germination | 400 mT, 30 min.; 600 mT, 30 min. (MF treatment on water sample) | 500 mT, 30 min. (MF treatment on water sample) | Massah et al. (2019) |
Shoot length, root length and seedling vigour index | 400 mT, 30 min.; 500 mT, 30 min. (MF treatment on water sample) | 600 mT, 30 min. (MF treatment on water sample) | |||
Mung bean ( |
Seed MF treatment | Protein contents in sprouts | 10 Hz, 1500 nT ± 250 nT; 100 Hz, 1500 nT ± 250 nT (all for 5 hr o day-1 for 15 days) | 50 Hz, 1500 nT ± 250 nT (5 hr o day-1 for 15 days) | Nair et al. (2018) |
Coffee ( |
Seed MF treatment | enzyme activity - EST | 28 mT, 6 days | 10 mT, 6 days | Júnior et al. (2020) |
Alfalfa ( |
Seed MF treatment | Growth parameters, protein contents and enzymes activity | 0.75 mT, 30 min o day-1, for 4 days | 1.5 mT, 30 min o day-1, for 4 days | Khaledi et al. (2019) |
Ryegrass ( |
Seed MF treatment | Seed germination capacity | 1000 Gs, 30 min.; 1500 Gs, 30 min.; 2000 Gs, 30 min. | 2500 Gs, 30 min. | Wang et al. (2010) |
Head cabbage ( |
Seed MF treatment | Seed germination | 1000–3500 Gs, 1–6 min. | Over 3500 Gs, over 6 min. | Cui et al. (2014) |
Cauliflower ( |
Seed MF treatment | enzyme activity - POD | 3000 Gs, 8 hr | 3500 Gs, 8 hr; 3500 Gs, 12 hr | Bao and Yun (2010) |
Cucumber ( |
Seed MF treatment | Seed germination capacity | 0.5 T (5, 10 min.); 1.0 T (5, 10 min.); 1.5 T (5, 10 min.) | 2.0 T (5, 10 min.) | Yu and Zhang (2010) |
EST, esterase; MF, magnetic field; MW, magnetised water; POD, peroxidase.
In recent years, the application of magnetism in agriculture and horticulture has been paid more and more attention to, especially in the field of MF treatment on both seed germination and the physiology of seedlings. In the application research of MF effects on seeds, for certain species and cultivars, only after a large number of screening tests to determine optimal dosage, can we achieve positive effects and income improvement. This is the main challenge we currently face for the commercial MF application in plants.
In the current application research of MF effects, much of the work, so far, has focused on how to improve economic traits and increase economic output. At the same time, more and more researchers have moved their attention to using seed MF treatment or MW irrigation to improve the plant stress tolerance under salt or heavy metal stresses, in order to achieve the purpose of soil restoration by plant heavy metal accumulation. At present, there have been many reports that MF treatment can successfully improve plant tolerance to various environmental stresses. They have all proved the potential of MF application in this area and provide new environmentally friendly ideas for soil restoration and environment protection. In addition, there are also reports on MF effect on seed anti-ageing ability, which imply that the magnetic treatment may also have a technical potential applied to seed storage.
On one hand, the future research direction is still to study in-depth the mechanism of MF effects on seed germination and cultivated crops growth promotion. It would help us to understand or even effectively predict the possible improvement of the crops’ parameters enhanced by the treatment. On the other hand, further research and development on the use of MF to improve plant stress tolerance are needed to achieve the application in soil remediation and environment protection on a large scale. Through these two aspects of further study and development can we make MF treatment more effective and targeted in agricultural and horticultural production and environment restoration.