Detection of NO₃^- introduced in plasma-irradiated dry lettuce seeds using liquid chromatography-electrospray...

Discharge plasma irradiates seeds with reactive oxygen and nitrogen species (RONS). However, RONS introduced in seeds by plasma irradiation have not been successfully detected thus far. This study provides experimental evidence that nitrate ion NO₃^- is introduced in lettuce seeds as RONS upon irradiation with atmospheric-pressure air dielectric barrier discharge plasma. Plasma irradiation for 5 min promotes seed germination. The components of the plasma-irradiated seeds were examined using electrospray ionization quantum mass spectrometry (ESI QMS), which revealed that the plasma irradiation introduced an ion with a mass of 62 m/z in detectable amounts. This ion was identified as NO₃^- by liquid chromatography (LC), multiple wavelength detector (MWD), and LC-ESI QMS. A one-dimensional simulation at electron temperature T_e = 1 eV, electron density N_e = 10¹³/m³, and gas temperature T_g = 300 K indicated the introduction of NO₃^-, involving nitric oxide NO. NO₃^- is one of the most important ions that trigger signal transduction for germination when introduced in seeds. The scanning electron microscopy (SEM) images revealed that there was no change on the surface of the seeds after plasma irradiation. Plasma irradiation is an effective method of introducing NO₃^- in seeds in a dry process without causing damage.