## 2 Materials and Methods
### Seed Treatment with CP, Vacuum, and EMF  
In order to determine the optimal duration for seed treatments, pilot experiments were performed to test the effect on germination by using irradiation with cold plasma (CP) for 2, 5, and 7 min, or treatment with radio frequency (RF) EMF for 5, 10, and 15 min. The optimal duration of treatments for seed germination in vitro were 5 min for CP treatment and 15 min for EMF. These durations of treatments were used in the study.  
A schematic diagram of the experimental setup for seed treatments with RF EMFs and CP with a device for optical emission spectroscopy (OES) analysis of the plasma species and measurement of the discharge characteristics is presented in Figure 1.  
Seed treatment with radiofrequency (RF) EMF was carried out by placing the dielectric container with seeds in the three-turn, water-cooled coil of the RF generator operating at 5.28 MHz. The characteristics of the EMF strength components in the axial zone of the coil were as described previously [24]. The amplitude values of the magnetic and electric components were 835 A/m (\(B\approx 1\) mT) and 17.96 kV/m, respectively. The treatment was performed in ambient air at atmospheric pressure and room temperature for 15 min (this treatment is abbreviated as EMF15).  
Low-pressure, capacitively coupled plasma was produced at a frequency of 5.28 MHz in a planar geometry reactor, consisting of two water-cooled copper electrodes (120 mm diameter) placed at a distance of 20 mm from each other in a stainless steel hermetic chamber. The RF voltage was applied to the upper electrode by the commutator (Figure 1). An open, sterile Petri dish with evenly dispersed seeds was placed on a grounded electrode. Seed treatment with CP was performed in open air at a pressure of 200 Pa, and the average value of the input power was 8.4 W (measured as described in [25]). The plasma parameters were as follows. The effective electron temperature T\({}_{\mathrm{e}}\approx 2.3\) eV, and the electron density n\({}_{\mathrm{e}}\approx 5\times 10^{8}\) cm\({}^{-3}\). Before igniting the discharge, the air was pumped from the chamber for about 7 min to reach the working pressure (such seed treatment with a vacuum was used as an additional control for CP treatment). The CP treatment lasted 5 min (this treatment is further abbreviated as CP5).  
Optical emission spectroscopy (OES) analysis was used to identify the active species produced in the plasma. Spectra were recorded in a range from 220 to 950 nm by a spectrometer equipped with a CCD (charge coupled device) area image sensor S10141 (Hamamatsu Photonics Norden AB, Sweden). During plasma treatment, molecular bands of nitrogen (second positive system) dominated in the OES spectra (Figure 2), and weak bands of N\({}_{2}\)\({}^{+}\) (first negative system) were observed. In the wavelength range of 220-320 nm, a number of oxygen-containing reactive species were recorded, such as nitric oxide and hydroxyl bands. However, the intensity of these molecular bands was relatively low.  
All experiments were performed in three replicates. The control, vacuum-, CP-, and EMF-treated seeds were stored at room temperature (19-22 \({}^{\circ}\)C) until germination tests.  
Figure 1: Schematic diagram of the experimental setup. 1 = RF generator, 2 = inductor, 3 = dielectric container with seeds, 4 = screen, 5 = commutator, 6 = vacuum chamber, 7 = powered electrode, 8 = lower electrode, 9 = Petri dish with seeds, 10 = measuring capacitor, 11 = window, 12 = oscilloscope, 13 = voltage probe, 14 = lens, 15 = spectrometer, and 16 = computer.