## 3 Results and Discussion
### Effects of Rice Stem Cell Extracts against Oxidative Damage on HFB
In addition, the micro DBD plasma electrode used in this study is characterized by a relatively weak energy intensity. The discharge energy value according to the nitrogen supply gas was 1.55 W per second. Therefore, the energy values according to the plasma treatment time were 93 (1 min), 279 (3 min), and 465 (5 min) W. Therefore, the threshold value that can activate cells is 300 W, and at energy intensities higher than that, it would have been in the range of energy that could cause damage rather than activation of the cells. Various studies have suggested that ROS play critical roles in cell differentiation [36]. We suggest that plasma-generated RONS could enhance the antioxidant activity of RSCE, which is involved in inducing the differentiation of HFB cells. Reactive species are well-known signaling molecules [37; 38; 39]. ROS and RNS produced by the plasma can be key factors in the expression of genes involved in plant cell proliferation. In our study, RNS generated from plasma were just the possible triggers for increasing the proliferation rates of rice callus cell. The beneficial effect of plasma-treated RSCE on oxidative damage may be due to the induction of the ability of fibroblasts to inhibit ROS. [PERSON] et al. [40] demonstrated that low concentrations (10-6 to 10-8 M) of H\({}_{2}\)O\({}_{2}\) and t-butyl hydroperoxide could stimulate growth in both primary fibroblast cultures and transformed baby hamster kidney fibroblasts (BHK-21). _Centella_ extract from the callus culture induced the expression of CAT exposed to H\({}_{2}\)O\({}_{2}\). It has been clearly shown that _Centella_ extract can prevent H\({}_{2}\)O\({}_{2}\) cytotoxicity by enhancing the ability of fibroblasts to scavenge harmful ROS [41]. To support this fact, the mRNA expression levels for catalase (CAT), a major antioxidant enzyme, were compared. Our qRT-PCR results showed that plasma-treated RSCE had excellent efficacy on the induction of antioxidants in fibroblasts (Figure 6). Plasma-treated RSCE improved the CAT expression level in cells damaged by oxidative stress after t-BHP treatment with a significant four times greater difference. This was improved by a factor of two compared  
Figure 5: Cell viability of HFB according to the plasma treatment time. All measurements were made in 3 or more than 3 replicates. * \(p<0.05\). with RSCE without plasma treatment. These qRT-PCR data suggested that the upregulation of cellular antioxidant enzymes is a major factor for the protective effect of RSCE, in which the antioxidant activity was enhanced by plasma treatment. Taken together, these results clearly demonstrated that the increased antioxidant capacity of plasma-treated RSCE could prevent oxidative stress by enhancing the ability of HFB to scavenge harmful ROS. It is considered that the relatively low energy and RONS generated from the plasma were at an appropriate level for activating RSCE rather than damaging it. Plasma treatment was able to enhance the antioxidant ability of RSCE and lowered the intracellular ROS level of HFB damaged by oxidative stress. The mRNA expression levels for catalase (CAT), a major antioxidant enzyme, were compared, and 1 mM of tert-butyl hydroperoxide (t-BHP) was used to artificially induce oxidative stress. Plasma-treated RSCE improved the CAT expression level in cells damaged by oxidative stress after t-BHP treatment, with a significant difference (* \(p<0.05\); ** \(p<0.01\)). 3\({}^{\prime}\) RSCE, extract of rice stem cells treated with plasma for 3 min. 0\({}^{\prime}\) RSCE, extract of rice stem cells without plasma treatment. In order to observe the t-BHP-induced cytotoxicity-prevention activity of plasma-treated RSCE, HFB cells were pretreated with RSCE (3\({}^{\prime}\) RSCE vs. 0\({}^{\prime}\) RSCE) at a concentration of 0.1 mg/mL and plasma-treated for 24 h before t-BHP treatment.