Methyl jasmonate elicitation increases vitexin production in protocorm-like body-derived cultures of Grammatophyllum speciosum Blume

Grammatophyllum speciosum Blume (Orchidaceae) is a giant orchid that accumulates phenolic glucosides and C-glycosylflavones, including the bioactive flavone vitexin. Vitexin is a pharmaceutically and cosmetically valuable compound obtained mainly from aerial tissues of wild-harvested plants, motivating controlled in vitro production. Methyl jasmonate (MeJA) is a widely used elicitor of phenylpropanoid and flavonoid biosynthesis; however, its effects on vitexin accumulation in protocorm-like bodies (PLBs) of G. speciosum in liquid culture systems have not yet been investigated. This study aimed to establish a PLB-derived liquid culture of G. speciosum and to evaluate the effects of MeJA (0, 50, 75, and 100 µM) on culture growth, phenolic and flavonoid accumulation, vitexin production, phenylalanine ammonia-lyase (PAL) activity, antioxidant capacity, and enzyme inhibitory activities. The cultures showed a sigmoidal growth profile with the highest dry growth index (DGI, 0.72 ± 0.09) on Day 32. MeJA elicitation for 12 days reduced biomass in a concentration-dependent manner (DGI 0.066 ± 0.007 to 0.050 ± 0.001 at Day 12 versus 0.089 ± 0.002 in untreated cultures), whereas the PLB clusters remained morphologically intact. Treatment with 75 µM MeJA gave the highest total phenolic (14.267 ± 0.273 mg GAE/g CDW) and total flavonoid (27.093 ± 0.504 mg QE/g CDW) contents. Vitexin was quantified by HPLC-DAD and its identity confirmed by LC-ESI-QTOF-MS; cultures treated with 75 µM MeJA contained 420.05 ± 9.96 µg vitexin/g culture dry weight, approximately twofold higher than untreated controls (208.33 ± 2.69 µg/g CDW). PAL activity was rapidly and transiently induced, peaking 12 h after 75 µM MeJA treatment. The same treatment also produced the highest DPPH (5.30 ± 0.20 mg TE/g CDW) and ABTS (10.64 ± 0.25 mg TE/g CDW) radical-scavenging and copper-chelating (6.54 ± 0.29 mg EDTA/g CDW) activities, and the strongest inhibition of collagenase (55.62 ± 0.34%), elastase (42.40 ± 0.63%), and tyrosinase (36.01 ± 1.71%). These results indicate that MeJA is associated with activation of the phenylpropanoid pathway and enhanced vitexin, phenolic, and flavonoid accumulation in G. speciosum . Overall, MeJA-elicited PLB-derived liquid cultures represent a controlled in vitro system for producing vitexin-containing extracts with antioxidant and enzyme-inhibitory activities.