153
Static, Low-Frequency, and Pulsed Magnetic Fields
Application of ELF-EMF alone or with vitamin E increased both SOD isoenzymes and
GPx activities compared with the control group. The results suggested that ELF-EMF
alters antioxidative activities of vitamin E in AT478 tumor cells.
Kaszuba-Zwoinska et al. (2010) investigated whether a PEMF can affect proliferation
and death of cancer cells. The U937 human lymphoid cell line was exposed to a PEMF
(50 Hz, 45 mT three times for 3 hours per each stimulation with 24-hour intervals)
during 4 days of cultivation. The PEMF potentiated density-induced death, both apoptosis and necrosis. Puromycin, a telomerase inhibitor, was used as a cell death inducer
at a concentration of 100 μg/mL. By contrast, combined interference of three doses of
puromycin and three times of PEMF stimulation resulted in a reduction of apoptosis
by 24.7% and necrosis by 13% compared with the same doses of puromycin alone. The
PEMF protects U937 cells against puromycin-induced cell death. The PEMF effects on
the human lymphoid cell line depend on cell density. Increased cell density induced cell
death and, in contrast, prevented cell death induced by puromycin.
3.4 Response of Plants and Microorganisms
to Magnetic Fields
These topics are promising research areas for applications to crop science, biotechnology, control of microbial growth and so forth. Recent studies on the effects of magnetic
fields on plant growth response are reviewed in Section 3.4.1. Recently proposed mechanisms of magnetotaxis are described in Section 3.4.2. Recent results of antibacterial
effects by magnetic fields are addressed in Section 3.4.3.
3.4.1 Plant Growth, Response, and Magnetotropism
Several magnetic treatments have been reported for improving germination parameters and biomass accumulation in various plants. The effects are assumed to be due
to increased photosynthetic efficiency (Shine, Guruprasad, and Anand 2011), enhanced
activities of hydrolyzing enzymes (Vashisth and Nagarajan 2010), reduced oxidative
stress (Hajnorouzi et al. 2011), and increased osmotic pressure (Cakmak, Dumlupinar,
and Erdal, 2010).
Vashisth and Nagarajan (2008) examined the effect of an SMF (≤250 mT) on the seeds
of chickpea (Cicer arietinum). Results showed that the SMF enhanced seed performance
significantly in terms of laboratory germination, speed of germination, seedling length,
and seedling dry weight compared with the unexposed control. However, the response
varied with field strength and duration of exposure without showing any particular
trend. Among the various combinations of field strengths and durations of exposure,
50 mT for 2 hours, 100 mT for 1 hour, and 150 mT for 2 hours gave the best results.
Exposure of seeds to these three SMFs improved seed coat membrane integrity as it
reduced the electrical conductivity of seed leachate. In soil, seeds exposed to these three
treatments produced significantly increased seedling dry weights of 1-month-old plants.
The root characteristics of the plants showed dramatic increase in root length, root surface area, and root volume. Such improved functional root parameters suggested that
Static, Low-Frequency, and Pulsed Magnetic Fields
Application of ELF-EMF alone or with vitamin E increased both SOD isoenzymes and
GPx activities compared with the control group. The results suggested that ELF-EMF
alters antioxidative activities of vitamin E in AT478 tumor cells.
Kaszuba-Zwoinska et al. (2010) investigated whether a PEMF can affect proliferation
and death of cancer cells. The U937 human lymphoid cell line was exposed to a PEMF
(50 Hz, 45 mT three times for 3 hours per each stimulation with 24-hour intervals)
during 4 days of cultivation. The PEMF potentiated density-induced death, both apoptosis and necrosis. Puromycin, a telomerase inhibitor, was used as a cell death inducer
at a concentration of 100 μg/mL. By contrast, combined interference of three doses of
puromycin and three times of PEMF stimulation resulted in a reduction of apoptosis
by 24.7% and necrosis by 13% compared with the same doses of puromycin alone. The
PEMF protects U937 cells against puromycin-induced cell death. The PEMF effects on
the human lymphoid cell line depend on cell density. Increased cell density induced cell
death and, in contrast, prevented cell death induced by puromycin.
3.4 Response of Plants and Microorganisms
to Magnetic Fields
These topics are promising research areas for applications to crop science, biotechnology, control of microbial growth and so forth. Recent studies on the effects of magnetic
fields on plant growth response are reviewed in Section 3.4.1. Recently proposed mechanisms of magnetotaxis are described in Section 3.4.2. Recent results of antibacterial
effects by magnetic fields are addressed in Section 3.4.3.
3.4.1 Plant Growth, Response, and Magnetotropism
Several magnetic treatments have been reported for improving germination parameters and biomass accumulation in various plants. The effects are assumed to be due
to increased photosynthetic efficiency (Shine, Guruprasad, and Anand 2011), enhanced
activities of hydrolyzing enzymes (Vashisth and Nagarajan 2010), reduced oxidative
stress (Hajnorouzi et al. 2011), and increased osmotic pressure (Cakmak, Dumlupinar,
and Erdal, 2010).
Vashisth and Nagarajan (2008) examined the effect of an SMF (≤250 mT) on the seeds
of chickpea (Cicer arietinum). Results showed that the SMF enhanced seed performance
significantly in terms of laboratory germination, speed of germination, seedling length,
and seedling dry weight compared with the unexposed control. However, the response
varied with field strength and duration of exposure without showing any particular
trend. Among the various combinations of field strengths and durations of exposure,
50 mT for 2 hours, 100 mT for 1 hour, and 150 mT for 2 hours gave the best results.
Exposure of seeds to these three SMFs improved seed coat membrane integrity as it
reduced the electrical conductivity of seed leachate. In soil, seeds exposed to these three
treatments produced significantly increased seedling dry weights of 1-month-old plants.
The root characteristics of the plants showed dramatic increase in root length, root surface area, and root volume. Such improved functional root parameters suggested that