## 4 Discussion  
We investigated the effect of plasma-activated water (PAW) on the early growth and development of _Arabidopsis_ in this study. The physicochemical properties of the plasma-activated water were detected according to the plasma exposure time, and the effect of the altered physicochemical properties of the PAW on plant growth was examined in _Arabidopsis_. The morphological differences in the roots and vegetative tissues, differences at the cellular level, and molecular biological differences were investigated. In addition, possible molecular mechanisms underlying the effect of the PAW treatment on  
Figure 6: PAW treatment induces gene expression of root hair initiation and elongation genes in _Arabidopsis_. Student’s _t_-test compared with D.W. \(p<0.05\) *, \(p<0.01\) **, \(p<0.001\) ***. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **DW** & **PAW5** & **PAW19** \\ \hline Root hair number & 15.14 \(\pm\) 2.47 & 24.57 \(\pm\) 3.10 *** & 26.85 \(\pm\) 5.33 *** \\  & (n = 7) & (n = 7) & (n = 7) \\ Root hair length (\(\mu\)m) & 162.92 \(\pm\) 29.10 & 77.40 \(\pm\) 7.21 *** & 54.33 \(\pm\) 7.83 *** \\  & (N = 50) & (N = 50) & (N = 50) \\ Root epidermal cell (\(\mu\)m) & 133.01 \(\pm\) 12.67 & 141.33 \(\pm\) 11.45 *** & 110.46 \(\pm\) 9.38 *** \\  & (N = 50) & (N = 50) & (N = 50) \\ \hline \hline \end{tabular} For the root hair number, “n” indicates the number of individual plants; for the root hair length from the root epidermal cells, “N” indicates the individual root hairs measured from a total of 7 samples. The GFP signals for root hair under, root hair length and root epidermal cell were measured under a Nikon-A1 confocal microscope at 488 nm with a eyepiece lens (10\(\times\)), objective lens (20\(\times\)). The results in the Table are the mean \(\pm\) SD (Student’s _t_-test compared with DW \(p>0.05\) ns, \(p<0.05\) *, \(p<0.01\) **, \(p<0.001\) ***).  
\end{table} 
Table 5: Root hair number and length of _A. thaliana_ L. (_WER:GFP/cbl9-1_) grown for 7 days after planting. plant growth were explored in _Arabidopsis_ based on the phenotype. We found that PAW facilitated the growth of the _Arabidopsis_ by modulating developmental genes at an early developmental stage. In recent years, plasma devices have emerged as an eco-friendly alternative method to improve plant growth and development. The application of plasma-related treatments in plants has been studied for improving seed germination, plant growth, plant height and yield in crops. The differences in plant phenotypes are caused by the difference in physical and chemical properties with increased biochemical components, altered seed coat morphology, biochemical activities, and altered gene expression [5; 6; 7; 8; 18]. The degree of difference in a plasma-induced plant phenotype is due to a variety and range of RONS (reactive oxygen and nitrogen species) generated by plasma with different feeder gases or just air [39]. Low pressure dielectric barrier discharge generates Ar/O\({}_{2}\), and plants treated with Ar/O2 produce increased H\({}_{2}\)O\({}_{2}\) in the roots and shoots of wheat [40]. Cylinder double dielectric barrier discharge (DBD) reactors generate nitrate (NO\({}_{3}\)\({}^{-}\)) and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) that positively regulate growth and germination in seeds [18; 19]. Even in _Arabidopsis_ as a model plant, PAW generated by air dielectric barrier discharge activates growth and development such as the leaf area, the number of flowering plants and the leaf number over a long-term observation period, and this phenomenon is also partly explained by the elevated hydrogen peroxide and nitrate [7]. In this study, the plasma generated by the SDBD device was confirmed to have a nitrogen molecule spectrum in the region of 290-400 nm (Figure 1). Nitrogen ions are mainly produced due to the plasma effect and react with H\({}_{2}\)O. When they ionize into NO\({}_{2}\)- and NO\({}_{3}\)\({}^{-}\), the pH decreases, and the conductivity increases.