###### Abstract  
To enhance plant pant endothelin (CPT) production _in vitro_, 5-month-old _Ophiorrhiza rideyama_ Craib plant cultures were treated with solutions of methyl jasmonate (MeJA) dissolved in ethanol, which were applied to the surface of the solid culture medium. It was demonstrated that the maximum CPT content in the tissue-cultured plants was achieved after 12 h elicitation with 50 uM MeJA. The mean CPT contents in roots and stems were 50.8 and 67.0 ug/g DW, respectively, which were approximately 1.8- and 2.6-fold higher, respectively, than those of the control. However, MeJA elicitation showed no significant effect on CPT accumulation in _O. rideyama_ leaves. Moreover, it was found that direct electric current (DC) stimulation also significantly increased CPT accumulation in _O. rideyama_. The treatment with DC at 20 mA for 3 min of stimulation enhanced 3-fold the CPT content in roots, stems, and leaves to 41.9, 36.0 and 19.6 ug/g DW, respectively, which were approximately 1.5-, 1.7- and 1.4-fold higher, respectively, as compared to those of the control. The results demonstrate that preharvest treatment by MeJA elicitation and electrical stimulation can be beneficial for secondary metabolite production of CPT in tissue-culture plants of _O. rideyama_. captothecin; _Ophiorrhiza rideyama; in vitro_ plants; elicitation; methyl jasmonate; electrical stimulation 26 March 2021 11 May 2021 1  
culture technology, is a promising alternative strategy [11]. The production of secondary metabolites by genetically engineered plant cell culture has become an important topic because of a shortage of natural resources and subsequent environmental concerns [1]. Recently, tissue-culture CPT-producing _Ophiorrhiza_ (Rubiaceae) species have attracted attention as alternative sources for CPT production [12]. Camptothecin is synthesized by a number of _Ophiorrhiza_ species, e.g., _O. liukiuensis_ and _O. kuroiwai_[4], _O. prostrata_[13], _O. alata_[10], _O. pumila_[14], and _O. mungos_[5]. One approach to promote plant tissue metabolism is by using elicitors [15]. The treatment of plant cells with biotic elicitors, such as bacterial and fungal cell walls, yeast extract and microbial homogenate, or abiotic elicitors, such as jasmonic acid and methyl jasmonate (MeJA), is a useful strategy to enhance production in cell/organ cultures of secondary metabolites, such as terpenoids, flavonoids, phenolic, alkaloids, and phytoalgebras [16; 17; 18]. Methyl jasmonate and its derivatives are important signal transduction molecules widely used as elicitor compounds for induction of secondary metabolites in many plant species and in plant cell and callus cultures [19; 20]. Enhanced accumulation of secondary metabolites in _in vitro_ culture systems using MeJA has been frequently reported. Methyl jasmonate acts as a signal transducer to promote _in vitro_ production of CPT from multiple shoots of _O. mungos_ var. _angustifolia_ in liquid culture medium [21]. The _in vitro_ production of the secondary metabolite plumbagin in roots and shoots of _Drosera burmanii_ in half-strength Murashige and Skoog (1/2 MS) liquid medium was enhanced after elicitation for 6 d with 50 uM MeJA [22]. In addition, preharvest MeJA application to 2-year-old raspberry and blackcurrant plants as a foliar spray significantly increased the synthesis of flavonoids, particularly, ellagic acid, quercetin and myricetin [23]. Accumulation of secondary plant compounds can also be induced by physiology--electrical stimulation. Electrical stimulation has shown to have effects on living cells, including plant cells. Pulsed electric field treatment is a promising tool to induce various biological effects for cellular compound stimulation [24]. However, research on the effects of electricity on plant response is quite limited. Electric current is a flow of electric charge carried by moving electrons through conductors or semiconductors or by ion in an electrolyte, which is measured in ampere (A) [25].