Increase of secondary metabolites in sweet basil (Ocimum basilicum L.) leaves by exposure to N₂O₅ with plasma technology

Exposure to N₂O₅ generated by plasma technology activates immunity in Arabidopsis through tryptophan metabolites. However, little is known about the effects of N₂O₅ exposure on other plant species. Sweet basil synthesizes many valuable secondary metabolites in its leaves. Therefore, metabolomic analyses were performed at three different exposure levels [9.7 (Ex1), 19.4 (Ex2) and 29.1 (Ex3) μmol] to assess the effects of N₂O₅ on basil leaves. As a result, cinnamaldehyde and phenolic acids increased with increasing doses. Certain flavonoids, columbianetin, and caryophyllene oxide increased with lower Ex1 exposure, cineole and methyl eugenol increased with moderate Ex2 exposure and l-glutathione GSH also increased with higher Ex3 exposure. Furthermore, gene expression analysis by quantitative RT-PCR showed that certain genes involved in the syntheses of secondary metabolites and jasmonic acid were significantly up-regulated early after N₂O₅ exposure. These results suggest that N₂O₅ exposure increases several valuable secondary metabolites in sweet basil leaves via plant defense responses in a controllable system.