## 3 Materials and Methods
### Identification of ROS and RNS Generated in the Applied APPJ Source  
Considering the close interactions between APPJ and the seeds artificially inoculated with plant pathogenic bacteria, the antimicrobial effect should be driven directly by reactive species of a short lifespan and showing a high oxidative capability.  
In order to identify the ROS and RNS produced during APPJ operation, OES was used. This instrumental technique allowed us to characterize the gaseous phase of APPJ. For OES measurements, a high-resolution Shamrock SR500 spectrograph (ANDOR, Abingdon, UK) was implemented. The OES spectrograph was equipped with a CCD camera (Newton DU-920P-OE, Andor, UK) cooled to \(-65\)\({}^{\circ}\)C, and two gratings: 1800 and 1200 grooves per mm, for the spectral regions of 200-400 nm and 400-900 nm, respectively. The CCD detector operated in FVB (full vertical binning) mode with an integration time of 0.1 s. For processing and acquisition of the APPJ spectra, the Solis S software v 4.32(ANDOR, UK) was used. The emission from the APPJ tip was imaged onto the spectrograph's entrance slit (10 um) using a UV achromatic lens (f = 60). The APPJ spectra in the 400-900 nm range were measured with an additional cut-off (<380 nm) WG5 filter (Zeiss, Jena, Germany).  
To determine which specific ROS and RNS are mainly generated for the studied APPJ system, experiments involving the degradation of MB and 4-NP were performed. In terms of the first assay, 0.01 g L\({}^{-1}\) MB solution (Avantor Performance Materials, Gliwice, Poland) was prepared according to good laboratory practice. Then, the resultant solution was transferred to the 24-well test microplate. The degradation experiments were performed in three repetitions under optimal APPJ conditions, maintaining a distance of 2 cm from the liquid surface, while the treatment time was 2 min. After APPJ treatment, the MB solution was transferred into quartz cuvette and the absorbance value was measured at 664 nm using a Specord 210 Plus UV/Vis spectrophotometer (Analytik, Jena, Germany). The effectiveness of APPJ application was presented as the degradation percentage referring to the absorbance values of the not-treated MB solution. The experiment was conducted with three technical replicates.  
In the second experiment, a 1 mM solution of 4-NP (Avantor Performance Materials, Poland) was prepared. A total of 2.00 mL of the obtained solution was transferred to the 24-well test microplate. The degradation process involving the APPJ source was evaluated in the same manner as for the MB degradation. The post-treatment 4-NP solution was transferred into a quartz cuvette, and a spectral scan from 200 to 600 nm with ascan speed of 50 nm/s and step 0.5 nm was acquired using a Specord 210 Plus UV/Vis spectrophotometer. The maximum absorbance determined from the spectral scan at 318 nm was used to determine the degradation efficiency of 4-NP, and the results were presented as degradation percentage referenced to the absorbance values for the not-treated 4-NP solution. In all experiments, deionized water was used throughout. The experiment was conducted with three technical replicates.