## 2 Results and Discussion
### Impact of the Optimized APPJ Treatment on Seed Germination and Early Plant Growth
Despite focusing on seed germination, we also examined early plant growth, which was determined based on the length of the sprouts formed from the APPJ-exposed seeds in relation to the corresponding controls. In the case of _Cucumis sativus_, _Pisum sativum_, and _Vigna radiata_ seedlings, no statistically significant differences were noted between the mean length of the APPJ-treated groups and the corresponding controls; therefore, no impact of the CAPP exposure on early plant growth was concluded regarding the above-listed three plant species (Figure 4). The sole noted statistically significant positive effect in this experiment concerned promotion of the early growth of _Zea mays_ sprouts by 20.96% due to APPJ treatment (Figure 4). In the current research, the effective eradication of phytopathogens from the seed surface, in addition to the non-harmful effect of the application of APPJ on the seed germination and the development of the examined plant species, confirmed the potential of CAPP-based technology as a tool for agricultural purposes. As already mentioned, there is a constant need for eco-friendly, innovative solutions to improve the quality of the crops and quantity of the generated yield. In the future, CAPP, due to its pro-ecological nature, ease of operation, and cost-effectiveness, may be widely used by seed producers or growers, but before a comprehensive assessment of the benefits and risks of standalone processes  
Figure 4: The effect of the CAPP treatment on the mean seedling length of the examined plant species. The exposure of the seeds to the APPJ lasted for 2 min. Bars correspond to means \(\pm\) standard errors. The asterisk marks a statistically significant difference between the untreated control and the treated sample (Welch’s test at \(p<0.05\)). involving an APPJ unit or integration of this methodology into the processing chain is highly needed [31]. The Reactive Nitrogen and Oxygen Species Produced During APPJ Exposure Conducted Under the Optimal Working Conditions  
The emission spectrum of the APPJ system is presented in Figure 5. As can be observed from Figure 5A, in the UV region (200-400 nm), the OH (A-X) and N\({}_{2}\) (C-B) emission bands were excited. The main bands of OH (A-X) were noted at 282.9 nm (1-0 transition) and at 308.9 nm (0-0 transition). The UV spectrum of APPJ was also dominated by numerous N\({}_{2}\) (C-B) bands with the band head at 315.9 nm (1-0), 337.1 nm (0-0), 353.7 nm (1-2), 357.7 nm (1-2), 375.5 nm (1-2), 375.5 nm (1-3) and 380.5 nm (0-2). Additionally, a strong N\({}_{2}\)\({}^{+}\) (B-X) band at 391.4 nm (0-0) was noticed. In the UV-NIR region (400-900 nm) (Figure 5B), the He atomic lines (He I) were noted at 587.5 nm, 667.8 nm, 706.5 nm, and 728.1 nm. Additionally, the atomic lines of H at 486.1 nm and 656.2 nm and the atomic lines of O (O I) at 777.2 nm, 772.4, and 844.6 nm were also revealed. The above-described outcomes pointed to the formation of the following ROS and RNS, i.e., OH, N\({}_{2}\), N\({}_{2}\)\({}^{+}\), O, as well as H, and He, by the examined APPJ system. Subsequently, colorimetric assays based either on degradation of methylene blue (MB) or 4-nitrophenol (4-NP) were conducted to obtain a better insight into specific ROS produced by the implemented APPJ source, working under the defined optimal conditions. It should be stressed that the degradation process of MB is mainly driven by ROS such as O\({}_{3}\), \({}^{1}\)O\({}_{2}\), \({}^{\bullet}\)OH, \({}^{\bullet}\)HO\({}_{2}\), and \({}^{\bullet}\)O\({}_{2}\)\({}^{-}\) produced during APPJ operation [59; 60]. As can be seen in Figure 6, the degradation of MB reached 42% \(\pm\) 3.62% within 2 min of the APPJ treatment. It suggests significant CAPP-mediated production of radicals, along with O\({}_{3}\) and O, as revealed by the MB degradation process. According to the literature [61], the oxidative potential of ROS responsible for MB degradation should be sufficient for the herein observed bactericidal effect.