## 4 Discussion
This could be explained by the different types of equipment used (the capacitively coupled low-pressure CP device in this study and the atmospheric DBD plasma device in [13]), as well as the parameters used for seed treatment (e.g., treatment dose) or the dependence of the effects on plant cultivars. All mentioned factors could cause different treatment outcomes (as shown in [14, 15]). Sexual dimorphism was observed in the response of hemp to CP5 treatment, as the same treatment increased the height and weight of the male plants (Figure 5). A strongly positive effect from the EMF15 treatment on hemp germination and growth was observed. An increase in the germination yield in vitro (by >30%) was followed a substantial increase in the growth of the above-ground part in both female and male plants, as well as the increased number of female infloresances (by 70%) (Figure 5). Thus, the obtained results indicate that seed treatment via EMFs could be used to increase the bioproduction of industrial hemp. The antioxidant activity of the leaves was negatively affected by EMFs (but to a lesser extent when compared with CP5), and the observed decrease in the amount of CBDA and CBD was not statistically significant. It remains to be established if such changes can affect the defense mechanisms of plants. Taking into account a strong positive effect on the leaf biomass and the number of infloresances, it might be concluded that the yield of CBD and CBDA produced per plant in the EMF15 group could be accordingly higher when compared with the control. Seed treatment with a vacuum did not induce changes in seed germination and plant morphometric parameters (Table 1 and Figure 5). However, biochemical analysis revealed a follow-up response of plants to vacuum treatment. Radical scavenging activity in the leaves was reduced, whereas the amount of CBDA was increased and the amount of CBD decreased in the female infloresances. Such a finding provides an interesting example of a hidden plant response to stress experienced by the seeds, and this has to be studied in more detail in the context of possible applications of seed treatment with a vacuum to increase the amount of biosynthesized CBD in industrial hemp. Thus, our results show that short (5-15 min) seed exposure to three different physical stressors (CP, a vacuum, and EMFs) resulted in stressor-specific effects on seed germination, plant growth, and secondary metabolism. In comparison with the vacuum or EMFs, low-pressure CP is a more complex stressor consisting of multiple components, such as low pressure, UV radiation, electrical discharge, electromagnetic field, and reactive plasma particles [40]. The performed OES analysis showed that nitric oxide NO- and hydroxyl radical OH- (Figure 2) were the dominating forms of reactive particles produced by the equipment used for hemp seed treatment with CP in this study. These two highly reactive species are also known as universal regulators of signaling processes in plants [41; 42] and, together with numerous other ROS (reactive oxygen species) species, may contribute to the stimulation or inhibition of seed germination [43]. However, most studies have attempted to explain the interaction between plasma particles and seeds by the processes that occur on the seed surface or the treated seed coat. The simplest and most popular explanation is that seed germination is stimulated by etching or chemical modifications of the seed coat, followed by an increase in seed hydrophilicity (wettability) and the facilitated penetration of water in a dry seed after imbibition [44; 45; 46]. However, other reports do not support this explanation, since germination can be stimulated by CP in the absence of surface etching [24; 47]. Moreover, supra-optimal CP doses inhibit seed germination, despite the increased wettability [48]. Numerous reports have been published recently showing that the effects of physical stressors on seed germination are far more complex and involve multiple responses to internal seed processes.