# A Coaxial Dielectric Barrier Discharge Reactor for Treatment of Winter Wheat Seeds
## 3 Results and Discussion
### Effects on Seed Germination of Wheat Treated with Argon and Helium Plasmas  
Germination tests were performed with control groups (untreated seeds and seeds subjected to gas only) and plasma-treated seeds for different exposure times (Figure 7). Plant seed germination showed a typical course of germination speed: a lag phase within 24 h (time of imbibition and activation of metabolisms and physiological processes) followed by a log phase where germination speed rises (measured macroscopically by the appearance of the radiole), and finally, a slowdown of germination speed by reaching a plateau and the maximum value of germination. Figure 7 presents the germination analyzed for several time intervals for seeds treated with (a) argon and (b) helium. At given germination conditions, untreated wheat started germinating after around 15 h and reached 100% germination after 48 h. No statistical difference (two-way ANOVA) was observed between the control groups within the observation time (15-48 h), indicating that neither the gas nor the shaking movement stimulates germination. It is clear that plasma treatment with argon and helium using the shaking reactor did not harm the seeds even after 30 min of plasma treatment (6 times 5 min of direct exposure), where 100% germination was still achieved. For both gases, an acceleration of germination can be observed already for short treatment times. In case of the argon discharge, germination acceleration is further enhanced with an increase of exposition time, in which an increase from 11% for 3 min plasma treatment to  
Figure 6: Water contact angle of wheat seeds treated for different treatment times from 1 to 30 min using an argon (black curve) and helium (red curve) discharge. Gas control values for both gases are in the same range as the control points: argon control is 107\({}^{\circ}\)\(\pm\) 12\({}^{\circ}\) and helium control is 111\({}^{\circ}\)\(\pm\) 9\({}^{\circ}\). Curves were fitted with a logistic function. around 40% for 30 min plasma treatment of germinated wheat seeds was obtained in the first 15 h. Interestingly, for most of the plasma treatments, seed germination was already in the log-phase for the 15 h observation time and started the saturation course at 24 h for all plasma-treated seeds. Moreover, within the log-phase of germination, an enhancement of germination was observed with longer plasma treatment time (e.g., 3 min \(<\) 5 min \(<\) 15 min \(<\) 30 min). The cumulative germination values for all plasma-treated seeds were statistically significant (two-way ANOVA, _p_\(<\) 0.001-0.05, n = 4) compared to both control groups from 15 to 24 h of observation time, except for 3 min plasma treatment at 15 h of observation time. On the other hand, with the helium plasma treatment, the acceleration of germination was less pronounced compared to the argon case. Thus, only 3.5% enhancement for 3 min helium plasma-treated seeds to 6.5% enhancement for 30 min of helium plasma treatment was observed. Moreover, for the helium discharge case, the germination of wheat seeds was less enhanced with longer exposure times from 3 to 30 min; thus, the seeds were not significantly different from each other during the observation times of germination. Statistically significant differences (two-way ANOVA, _p_\(\leq\) 0.02, n = 4) between helium-treated seeds for all exposure times and control groups were only observed at 24 h germination time. A decrease of germination speed started beyond 27 h during germination. In comparison to the WCA measurements (Figure 6), similar trends were detected for seeds treated with argon and helium plasma. Those results could indicate that the further enhanced wettability of argon-treated wheat seeds for longer exposure times might be related to the improvement in water uptake and thus early germination. Moreover, the better performance of the argon treatment might be related to the higher intensities of excited oxygen species detected in the OES spectrum (Figure 4a).