## 3 Results
### PAW Modulates the Root Hair Density through Root Developmental Genes
\begin{table}
\begin{tabular}{l c c c c c c} \hline  & **DW** & **PAW5** & **PAW7** & **PAW12** & **PAW19** & **PAW40** \\ \hline Cotyledon size in the & & & & & & \\ leaf length direction & 0.60 \(\pm\) 0.03 & 0.77 \(\pm\) 0.09 *** & 0.81 \(\pm\) 0.09 *** & 0.84 \(\pm\) 0.09 *** & 0.88 \(\pm\) 0.10 *** & 0.96 \(\pm\) 0.14 *** \\ (mm) & (n = 30) & (n = 21) & (n = 25) & (n = 30) & (n = 15) & (n = 23) \\ Cotyledon size in the & 0.46 \(\pm\) 0.03 & 0.62 \(\pm\) 0.07 *** & 0.64 \(\pm\) 0.06 *** & 0.67 \(\pm\) 0.07 *** & 0.63 \(\pm\) 0.05 *** & 0.76 \(\pm\) 0.08 *** \\ leaf width direction & (n = 30) & (n = 21) & (n = 25) & (n = 30) & (n = 25) & (n = 23) \\ Palisade cell number & 48.20 \(\pm\) 6.83 & 43.20 \(\pm\) 8.19 ** & 45.40 \(\pm\) 5.59 ns & 47.40 \(\pm\) 5.85 ** & 48.40 \(\pm\) 5.59 ** & 40.40 \(\pm\) 5.51 ** \\  & (n = 5) & (n = 5) & (n = 5) & (n = 5) & (n = 5) & (n = 5) \\ Palisade cell size (μm) & 15.47 \(\pm\) 1.50 & 24.63 \(\pm\) 2.34 *** & 25.07 \(\pm\) 2.39 ** & 25.59 \(\pm\) 2.00 *** & 31.35 \(\pm\) 3.93 *** & 42.88 \(\pm\) 3.36 *** \\  & (N = 300) & (N = 300) & (N = 300) & (N = 300) & (N = 300) & (N = 300) \\ \hline \end{tabular} For the cotyledon size and palisade cell number, “n” indicates the number of individual plants, and for the palisade cell size, “N” indicates the individual palisade cells measured from a total of 5 individual samples. Single cotyledons were measured from each biological sample. The palisade cell number was counted from the cotyledon length direction. Results 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 3: Cotyledon size and palisade cell size and number of _Arabidopsis_ grown in the DW and PAW treatment condition at 10 days after planting. Because the differences in the root hair phenotype between the DW and PAW treatment conditions were significant at 5 days after planting (Table 4), a confocal microscope was used for imaging the root epidermal cell shape at 7 days after planting. To visualize the cell type in the root, we used three different treatment conditions, DW, PAW5, and PAW19. The roots of the _Arabidopsis WER:GFP_/_cob19_-1 line were grown for 7 days. Figure 5 shows the tagged _WER_ promoter with _GFP_, which resulted in the appearance of fluorescence in all the epidermal layers of the root cells. Quantification of the root hair numbers showed an increment in all the PAW treatment conditions compared to the DW treatment condition. In contrast, the root hair length was decreased in the PAW treatment condition compared to the DW treatment condition (Table 5, Supplementary Figure S2). Interestingly, the length of the root epidermal cells was elongated with a similar pattern to the root length phenotype after the PAW treatment, which is consistent with the root enhancement in the PAW5 and PAW7 and the reduction in the PAW19 treatment condition compared to the DW treatment condition. It is believed that there will be a specific mechanism regulating the number of root hairs and length of the root hair in the PAW condition during the plant development process. Moreover, the results indicate that PAW5 is the optimized condition for plant growth and development. To further understand the mechanism of PAW affecting the root development in _Arabidopsis_, we confirmed the expression of several marker genes related to root hair initiation and elongation. Previously, it was shown that the nitrate concentration could induce the expression of _COBL9_ which activates root hair initiation and elongation [34], _NT_COB9_ was upregulated by PAW treatment in tobacco [25]. As expected, the expression of _COBL9_ was significantly increased in the PAW5 treatment condition compared to the DW treatment condition. In contrast, the expression was suppressed in the PAW19 treatment condition. _AUXIN1_ (_AUX1_) and _LIKE-AUXIN_ (_LAX3_) are the key auxin influx carriers and are multi-membrane transmembrane proteins that transfer the auxin involved in