Influence of microwave frequency electromagnetic radiation on terpene emission and content in aromatic plants

Abstract

Influence of environmental stress factors on both crop and wild plants of nutritional value is an important research topic. The past research has focused on rising temperatures, drought, soil salinity and toxicity, but the potential effects of increased environmental contamination by human-generated electromagnetic radiation on plants have little been studied. Here we studied the influence of microwave irradiation at bands corresponding to wireless router (WLAN) and mobile devices (GSM) on leaf anatomy, essential oil content and volatile emissions in Petroselinum crispum, Apium graveolens and Anethum graveolens. Microwave irradiation resulted in thinner cell walls, smaller chloroplasts and mitochondria, and enhanced emissions of volatile compounds, in particular, monoterpenes and green leaf volatiles (GLV). These effects were stronger for WLAN-frequency microwaves. Essential oil content was enhanced by GSM-frequency microwaves, but the effect of WLAN-frequency microwaves was inhibitory. There was a direct relationship between microwave-induced structural and chemical modifications of the three plant species studied. These data collectively demonstrate that human-generated microwave pollution can potentially constitute a stress to the plants.

Keywords: Abiotic stress; Aromatic plants; Essential oils; Microwave; Volatile organic compounds.

Fig. 1

TEM images of cell walls in leaves of microwave-irradiated and control parsley: a) Control; b) GSM irradiated; c) WLAN iradiated.

Fig. 2

Changes in net assimilation rate (a) and stomatal conductance to water vapour (b) in 3 aromatic plants in response to microwave stress. The data are expressed per unit projected leaf area. Each data point is the mean (± SE) of 8 independent replicate experiments with a different plant. * and ^# demonstrates statistically significant differences between the microwave irradiated plants and control plants and between WLAN and GSM irradiated plants respectively (P < 0.05).

Fig. 3

Changes in terpene content (mg g⁻¹ FW) in Petroselinum crispum (a), Anethum graveolens subsp. hortorum (b) and Apium graveolens (c) foliage in response to microwave irradiations at bands corresponding to wireless router (WLAN) and mobile devices (GSM). Each data point is the mean (± SE) of three independent replicate experiments with a different plant. * and ^# demonstrates statistically significant differences between the microwave irradiated plants and control plants and between WLAN and GSM irradiated plants respectively (P < 0.05).

Fig. 4

Alteration of the emission of volatile organic compounds (nmol m⁻² s⁻¹) from foliage of Petroselinum crispum (a), Anethum graveolens subsp. hortorum (b) and Apium graveolens (c) in response to microwave irradiations at bands corresponding to wireless router (WLAN) and mobile devices (GSM) (presentation of statistical differences as shown in Fig. 2). Each number corresponds to a particular volatile compound as follows: 1. 1-hexanol; 2. (Z)-3-hexen-1-ol; 3. (E)-2-hexenal; 4. α-pinene; 5. camphene; 6. β-myrcene; 7. β-pinene; 8. α-phellandrene; 9. Δ-3-carene; 10. D-limonene; 11. para-cymene; 12. β-phellandrene; 13. (E)-β-ocimene; 14. 1,8-cineol; 15. iso-bornyl acetate; 16. longicyclene; 17. caryophyllene oxide; 18. α-selinene; 19. (Z)-β-farnesene; 20. α-caryophyllene; 21. geranylacetone. * and ^# demonstrates statistically significant differences between the microwave irradiated plants and control plants and between WLAN and GSM irradiated plants respectively (P < 0.05).