Favourable and Unfavourable Effect of Homogeneous Static Magnetic Field on Germination of Zea mays L . ( Maize ) Seeds

The effect of homogeneous static magnetic stimulation on Zea mays L. (maize) seeds and its potential utility as a tool in biotechnological development for the improvement of maize seeds was studied. The values of magnetic flux density that influenced the biological development of some plant species of the Poaceae family were determined from a literature review. ICA V-305 variety corn seeds were exposed to seven values of magnetic flux density between 50.0 mT and 250.0 mT, with homogeneity of 98.4% and at (1.0, 3.0, 5.0 and 7.0) min exposure times. The mean germination time (MGT), index of germination speed (VGer) and germination rate (Gmax) were evaluated as responses. The magnetic flux density of 50.0 mT with a one-minute exposure time recorded the largest reduction (12.4%) in the MGT while the germination rate for the same treatment increased by 17.4% with respect to the control. No significant effects of the magnetic treatment were recorded for the á . The magnetic treatment of seeds with homogeneous static fields does not have as favourable a response as the treatments with fields with magnetic gradients, that is to say, using toroidal magnets.


Introduction
Advances in the knowledge of the evolution of living beings under the presence of the geomagnetic field has generated interest in the study of magnetosensitivity of various organisms.Regarding plants, Belyavskaya presents an interesting review on the effect of the geomagnetic field in the biochemistry, physiology and biology of plants (Belyavskaya, 2004).Although there is a large number of reports, mainly in the area of agriculture, which indicate that plant systems respond when treated with magnetic field (Galland & Pazur, 2005;Maffei, 2014;Pietruszewski & Martinez, 2015;Teixeira da Silva & Dobránszki, 2015;De Sousa et al., 2016), magnetic stimulation of plant systems can be considered as a technique still in the research stage.In this sense, works can be found with barley, wheat, and oats, among others, and for maize seeds, effects are reported which are presented in Table 1.Seeds have gone through magnetic fields with values from microtesla to hundreds of millitesla, although there are studies of the response to stimuli in units of tesla.For this purpose, passive magnetic sources (permanent magnets) or active sources have been used: Helmholtz coils, electromagnets and/or solenoids (Table 1), in which the values of B, selected by the experimenters, and the values that generated favourable responses (B fav ) in the study variables are also recorded.
The results reported raise several levels of discussion, of which two can be taken into consideration.The first level corresponds to the need to determine which of the physical factors are determinant in this technique and how they should be controlled during exposure.Taking into account what was stated before, it is established that the biological effect of magnetic fields is dependent on factors such as the polarity of the field and the value of B it generates (Van, Teixeira da Silva, Ham, & Tanaka, 2011).Nevertheless, it is notorious that in the methodology of exposure reports selected in Table 1, few of them presented the values of homogeneity or gradient of the magnetic field.
The second level is aimed at identifying and explaining the cause of the biological effects observed from the processes activated at the biophysical and biochemical level, since the interpretation of these affectations can be contributed to the understanding of the mechanisms that are unchained in the plant under the effect of the magnetic treatment.The literature reports influence on enzymatic activation, imbibition (Vashisth & Nagarajan, 2010;Shine, Guruprasad, & Anand, 2011), enhanced reactive oxygen species content (Shine et al., 2017), variations in ionic currents (Socorro & García, 2012), modifications in water adsorption processes (Torres, Socorro, & Hincapie, 2018) and changes in the cellular membrane characteristics and RNA quantification (Goodman, Greenebaum, & Marron, 1995).For all the above mentioned reasons, the effect of homogeneous and intense static magnetic flux density on the germination of maize seeds are studied in the present work, unifying criteria that have been proposed in Valberg (1995), Kaune (1995), and Lee (1996) reports, where studies regarding to the physical variables involved through characterization of the magnetic field sources used in the experiments are presented.

Plant Material
Commercial Maize seeds (Zea mays L. cv.ICAV305, Semillas del Pacífico, Cartago, Colombia), fit between 1.000 and 2.000 MASL were used.The seeds without visible damage and with uniform morphology were pre-selected prior to the magnetic treatment.The preselected seeds were first sieved by passing them through a (8.0 × 8.0) mm mesh sieve, and later sieved using a (6.0 × 6.0) mm mesh sieve to homogenize the sample size separating seeds into large, medium and small sizes in order to use the medium size seeds which have 0.3878±0.0002g average mass and 0.356±0.008cm 3 average volume.jas.ccsenet.

Magne
The

In order to according
Where, Ni

Data A
The choice completely (Bartlett).Pairwise c
It was not possible to establish significant differences for the germination rate, but it must be clear that the control seeds showed a germination rate of 91.0%, which was reached by the seeds that received the magnetic treatments.
In analysing these results, it is important to highlight two distinctive features: first, the number of treatments with unfavourable results (five) was higher for the variables V Ger and MGT, which presented statistical differences between significant and highly significant (Tables 3 and 4).The second shows that for exposure with homogeneous static magnetic field, low dose treatments improve germination and high dose treatments decrease germination in MGT and V Ger .Note.The table shows the average value and the standard deviation for each of the treatments.The asterisk indicates differences with the control: **** (P < 0.001) very strongly significant, *** (0.001 < P < 0.01) strongly significant, ** (0.01 < P < 0.05) significant and * (0.05 < P < 0.1) differences.
When analysing these results, the positive and negative behaviour suggests that the characteristics of the magnetic fields, such as homogeneity or gradients, are probably influencing alterations in metabolism and/or the transport of phytohormones involved in the germination process.This can be interpreted as if the effect of the homogeneous and intense static magnetic field has a low positive response on the germinative processes in maize seeds.
However, by reviewing each of the references presented in detail and identifying the magnetic source and the factors related to the characteristics of the magnetic field with which the exposure was conducted, it was found that for works mentioned in Table 1 sources that show magnetic fields with spatial characteristics and parameters different between them and different from those used in this experiment have been used.In addition, in the methodology of exposure few presented homogeneity values or gradients.
Therefore, in order to compare the results of this work with those mentioned above, not only the value of B should be taken into consideration.The first step is to identify the type of source, whether a passive (magnets) or active source (coils, electromagnet or solenoid) were used, and if magnets were used, identify if they were toroidal or cylindrical or square bar magnets.Given that it must be clear that there is always some degree of heterogeneity in the spatial distribution of the magnetic field, which, when categorized in percentage terms from highest to lowest, appears with higher percentage in toroidal magnets, followed by cylindrical rods, solenoids, electromagnets and in much lower percentage in Helmholtz coils.For example, when comparing the images presented in Figure 1b and Figure 4, it can be observed that there is a magnetic field with high homogeneity in the electromagnet, while in toroidal magnets magnetic gradient values are very high besides a variation in the polarity can be observed, which suggests very different experiments (Torres, Hincapie, & Gilart, 2018).But, in order to have a high homogeneity value in the electromagnet, the samples must be positioned in the central zone between the cores since, otherwise, this value decreases drastically.
If the magnetic source was active, it is necessary to determine whether it was fed by DC or AC, since the energy density of a magnetic field AC (ρ AC ) is twice that of DC (ρ DC )-Equations 3 and 4-as well as to consider the exposure doses (D) which result from operating the field energy density with exposure time (t exp )-Equation 5-as discussed in (Pietruszewski & Martinez, 2015).et al. (2017) and Kataria et al. (2015), with similar magnetic flux densities but with higher magnetic field doses than those presented in this work, obtaining similar results to those presented by Flórez et al. (2007), that used toroidal magnets locating the seeds in the walls of the orifice of the toroidal magnet where the values of B change in magnitude, and direction and with a very low homogeneity (Figure 4), the latter having a very good germinative process improvement. jas.ccsenet.

Conclusions
Results presented in this work suggest that the stimulation with homogeneous static magnetic field compromises biological structures and interferes in relevant processes during the germination of Zea mays seeds for the magnetic flux densities and exposure times.
The treatment responses may be affected by different parameters of the magnetic field such as the gradients or the homogeneity of the magnetic flux density produced by the generators.This phenomenon indicates that the treatment with static magnetic field is better when conducted with field gradients, different to the results obtained with homogeneous fields.
Further research with magnetic seed treatment is needed to consolidate a standard procedure that defines the stimulation criteria in such a way as to ensure that the doses involved in the biological processes of the stimulated seeds are secured and that the results are reproducible under established conditions.
In order for the magnetic seed treatment to be profiled as an alternative for their improvement at the agricultural level, a unified application methodology must be developed, which is the result of the verification of which field parameter affects each seed parameter in the seeds and that allows the verification of the results of the investigations in this field and therefore the experimental reproducibility.
Figure 1 Figure 2. Image comparing the results of this study with those of previous reports, care should be taken with the interpretation of the results with stimulation in AC and those of experiments that were done with toroidal magnets.Consequently, when comparing the favourable results of this work with other works, we started by discarding those who worked in AC only leaving reports such as:Isaac et al. (2011), with (2.0, 4.0 and 6.0) mT at 3.0 min andZepeda et al. (2011), 480 mT (5.0, 10.0 and 15.0) min, which had exposure with static magnetic field generated with solenoids indicating lower homogeneity values, and the results ofVashisth andNagarajan (2009) and (2009a), with treatments of 100 mT, two hour and 200 mT, one hour that used electromagnet, Shine

Figure
Figure 4. D

Table 1 .
Maize seeds magnetic treatment experiments characteristics.N.I, no information

Table 3 .
MGT of the magnetic treatments studied

Table 4 .
Speed of germination of the studied magnetic treatments TreatmentV Ger (sem/h) Treatment V Ger (sem/h) Treatment V Ger (sem/h) Treatment V Ger (sem/h)