To investigate the effects of extremely low frequency magnetic fields on the photosynthetic activity of in vitro (micropropagation) coffee seedlings.
Coffee is an important commercial product. Micrpropagation presents an in vitro culture system to generate high quality coffee seedlings. After a six weeks establishment phase in a culture medium, the plants reach a multiplication phase usually having three pairs of leaves and a primary root at the end. Afterwards, in the acclimatization phase, plants are transferred to a pot with soil.
Seedlings were exposed or sham exposed either during establishment, multiplication, or acclimatization for 3 minutes. For each experimental group (exposure and sham exposure, respectively), 50 samples were used per replicate for all phases.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
60 Hz
Exposure duration:
3 minutes
|
|
| Frequency | 60 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 3 minutes |
| Exposure source | |
|---|---|
| Setup | electromagnet was formed by two parallel coils (dimensions 50 x 38 x 4 cm); coils were connected in series and coupled to a signal generator of sinusoidal waveform |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 2 mT | - | measured | - | ± 0.01 mT |
In exposed seedlings, the photosynthesis rate was significantly decreased during the establishment phase in comparison to the sham exposed seedlings, while during multiplication and acclimatization phase the photosynthesis rate was significantly increased. The transpiration was significantly decreased during all three phases in exposed seedlings when compared to the sham exposed ones, while the concentration of chlorophyll a and b was significantly increased. Additionally, the gene expression of the ribulose 1,5-bisphosphate carboxylase/oxygenase small subunit was increased in the exposed samples during the acclimatization phase compared to the sham exposure.
Scanning electron microscopy revealed significantly higher stomata ornamentation and thicker cuticulas during the establishment and multiplication phase in the exposed seedlings in comparison to the sham exposed seedlings as well as most condensed leaf parenchyma with abundant amyloplasts and xylem tubes with thicker walls. In the acclimatization phase the leaves of exposed seedlings showed an increased cuticular wax content and the xylem vessel thickness was significantly higher than in sham exposed plants.
The results indicate that extremely low frequency magnetic fields may improve the coffee seedling's quality by influencing the photosynthetic activity of the seedlings during the multiplication and acclimatization phase and increasing their vigor.
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