## 3 Results
### Effect of Electrical Stimulation on CPT Accumulation in O. ridleyana  
#### 3.3.1 Roots  
The present study indicated an influence of DC intensity on CPT accumulation in plant cultures of _O. ridleyana_. Roots of 5-month-old tissue culture plants of _O. ridleyana_ had higher CPT contents compared with stems and leaves. Average CPT concentrations in different parts of _O. ridleyana_ treated with DC current at 10-40 mA are shown in Table 4. The DC stimulation resulted in significant increases in CPT content in all parts of the tissue culture plants (Table 4 and Figures 7-9). The highest CPT content in roots at 41.9 ug/g DW was obtained from the stimulation by the DC current at 20 mA, followed by the stimulation at 30 mA, 40 mA and 10 mA, respectively.  
Figure 6: Effects of MeJA elicitation on CPT concentration in leaves by elicitation with ethanol and MeJA (20, 50 and 100 uM) for 12 h (\(\square\)) and 24 h (\(\blacksquare\)) before harvesting. The values are expressed as mean \(\pm\) SD (\(n\) = 3).  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{3}{c}{**CPT Content (\(\mu\)g/g DW)**} & \multicolumn{3}{c}{**CPT Content \({}^{\text{b}}\) (\(\mu\)g/ Culture Bottle)**} \\ \cline{2-7}  & **Root** & **Stem** & **Leaf** & **Root** & **Stem** & **Leaf** & **Total** \\ \hline Control & 27.3 \(\pm\) 1.3 & 21.3 \(\pm\) 3.0 & 13.8 \(\pm\) 2.7 & 1.5 & 1.4 & 2.6 & 5.5 \\ DC 10 mA & 33.5 \(\pm\) 3.8  & 36.0 \(\pm\) 2.7  & 2.3 & 2.4 & 3.8 & 8.4 \\ DC 30 mA & 36.4 \(\pm\) 4.8  & 16.7 \(\pm\) 3.0 & 2.0 & 2.1 & 3.2 & 7.3 \\ DC 40 mA & 34.7 \(\pm\) 3.3 [FOOTNOTE:]Footnote : calculation by using the average dry weight in Table 1.[ENDFOOTNOTE] & 26.1 \(\pm\) 1.8 & 16.0 \(\pm\) 3.4 & 1.9 & 1.8 & 3.1 & 6.7 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Average CPT concentrations in different parts of 5-month-old tissue culture plants of \(O\). _ridleyana_ treated with DC current at 10–40 mA and the estimated CPT content per 30 mL culture bottle.  
Figure 8: Effects of DC intensities (10, 20, 30 and 40 mA) on CPT accumulation in \(O\). _ridleyana_ stems. The values are expressed as mean \(\pm\) SD (\(n=3\)); a: significant at \(p<\) 0.05 vs. control.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multirow{2}{*}{**Incubation Time (h)**} & \multicolumn{3}{c}{**CPT \({}^{\text{a}}\) Content (\(\mu\)g/ Culture Bottle)**} \\ \cline{3-6}  & & **Root** & **Stem** & **Leaf** & **Total** \\ \hline Control & - & 1.5 & 1.7 & 2.4 & 5.7 \\ \hline Ethanol & 12 & 1.7 & 1.6 & 2.4 & 5.8 \\  & 24 & 1.4 & 1.4 & 2.6 & 5.4 \\ \hline MeJA 20 \(\mu\)M & 12 & 1.9 & 1.7 & 2.7 & 6.3 \\  & 24 & 1.9 & 1.9 & 2.7 & 6.5 \\ \hline MeJA 50 \(\mu\)M & 12 & 2.8 & 4.5 & 3.0 & 10.3 \\  & 24 & 1.8 & 3.3 & 2.7 & 7.8 \\ \hline MeJA 100 \(\mu\)M & 12 & 1.7 & 1.7 & 2.3 & 5.7 \\  & 24 & 1.9 & 1.6 & 2.2 & 5.7 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The estimated CPT content per 30 mL culture bottle of 5-month-old tissue culture plants of \(O\). _ridgeana_ treated with MeJA in ethanol (0–100 \(\mu\)M) compared to the control.  
Figure 7: Effects of DC intensities (10, 20, 30 and 40 mA) on CPT accumulation in \(O\). _ridleyana_ roots. The values are expressed as mean \(\pm\) SD (\(n=3\)); a: significant at \(p<\) 0.05 vs. control.  
TheHPLC chromatograms obtained from \(O\). _ridleyana_ roots of those treated with DC 20 mA showed a much larger peak area than those of the untreated controls (Supplementary Materials). It was also demonstrated that CPT concentrations in roots of all treated plants by DC stimulation were significantly higher in comparison to that of the untreated plant, which contained CPT at 27.3 \(\mu\)g/g DW.