## 2 Effect of Plasma on Seed Germination
[17] compared different plasma sources for buckwheat seed germination and found that a GlidArc plasma source with an air feeder gas induced improved germination compared to downstream microwave plasma, planar rotating electrode plasma, and surface dielectric barrier discharge plasma. Other studies have reported variations in seed germination efficiency among plant species when treated with the same plasma source (Tables 1 and 2) [9; 13; 14; 16; 46; 50; 56; 57; 65]. Most studies identified an optimal treatment time for the best germination efficiency for each plant species and plasma source. Effects of the feeding gases on the plasma-mediated seed germination have also been reported. [PERSON] et al. [32] found that mung bean seed germination was most efficient with microplasma generated in an aqueous solution using oxygen as the feeding gas, as opposed to helium, nitrogen, and air. [PERSON] et al. [35] reported germination increases of 24, 28, and 35.5% for DBD plasma-treated wheat seeds with air, nitrogen, and argon feeding gases, respectively. Most studies have been under laboratory conditions, but field-based investigations have also been reported [14; 44]. [PERSON] et al. [14] observed a 10-20% increase in the field germination capacity of soy, honey clover, and catgut seeds with microwave plasma treatment, whereas [PERSON] et al. [44] did not observe any changes in the germination percentage. The mechanisms of enhanced seed germination by plasma have been thoroughly investigated. The most frequently reported factors are changes in the physical and chemical properties of the seed coat or surface. Physical and chemical changes to the seed surface can result in elevated hydrophilicity and water permeability that enhances water imbibition, which is required for seed germination. Increased hydrophilicity and water permeability of the seed surface after plasma treatment has been frequently observed [16; 68; 69]. Chemical changes and leaching of the seed surface membrane have also been analyzed in many studies [14; 18; 34; 42; 68]. Cold atmospheric pressure plasma decreases the water contact angle from 115\({}^{\circ}\) to 0\({}^{\circ}\) and modulates the hydrophilicity of the seed surface, which increases the uptake of water and initiates subsequent biochemical processes [16]. Similarly, [PERSON] et al. [18] reported that cold plasma treatment decreases the contact angle of soybean seeds from 70.14\({}^{\circ}\) to 20.94\({}^{\circ}\). There is abundant data to support the plasma-induced changes in the physicochemical properties of the seed surface and the increases in water absorption. However, enhanced seed germination was also observed without increased hydrophilicity of the seed surface [34]. The surface of quinoa seeds treated with RF plasma was chemically modified, but the hydrophilicity of the seed surface did not change. Nitrogen oxide (NO\({}_{\rm X}\)-) and potassium (K\({}^{+}\)) ions accumulated on the seed surface via chemical alterations from the plasma treatment and penetrated the seeds after water addition, providing nutrients for seed germination. Another possible mechanism for plasma-induced enhanced seed germination is that the biochemical and molecular processes inside the seed are activated by plasma generated reactive oxygen and nitrogen species (RONS). Plasma generates a diverse range of RONS, depending on the feeder gas. These RONS can act as signaling molecules and initiate a germination cascade [70]. Reactive oxygen species (ROS) facilitate the oxidation of the aleurone layer and the mobilization food reserves during seed germination. [PERSON] et al. [71] showed that RF cold plasma (at low pressure) treatment (7 min) increased the GA (gibberellic acid) content of sunflower seeds and increased the germination rate by 10-24%. Increased GA promotes the activity of \(\alpha\)-amylase, which degradescomplex starches to metabolize sugar to initiate the germination process [71].