Salinity is a major abiotic factor affecting plant growth and secondary metabolism. However, no information is available about its effects on Schizonepeta tenuifolia Briq., a traditional Chinese herb. Here, we investigated the changes of plant growth, antioxidant capacity, glandular trichome density, and volatile exudates of S. tenuifolia exposed to salt stress (0, 25, 50, 75, 100 mM NaCl). Results showed that its dry biomass was reduced by salt treatments except 25 mM NaCl. Contents of antioxidants, including phenolics and flavonoids, increased at low (25 mM) or moderate (50 mM) levels, but declined at severe (75 and 100 mM) levels. On leaf surfaces, big peltate and small capitate glandular trichomes (GTs) were found. Salt treatments, especially at moderate and severe concentrations, enhanced the density of total GTs on both leaf sides. The most abundant compound in GT volatile exudates was pulegone. Under salinity, relative contents of this component and other monoterpenes decreased significantly; biosynthesis and accumulation of esters were enhanced, particularly sulfurous acid,2-ethylhexyl hexyl ester, which became the second major compound as salinity increased. In conclusion, salt stress significantly influenced the growth and secondary metabolism of S. tenuifolia, enabling us to study the changes of its pharmacological activities.

Schizonepeta tenuifolia is a medicinal plant whose bioactive monoterpenoids, such as pulegone, are biosynthesized and stored in peltate glandular trichomes. Although jasmonate signaling is known to promote trichome development and terpenoid accumulation, the underlying transcriptional regulators in S. tenuifolia remain unknown. Here, we identified two jasmonate-responsive MYC2-type transcription factors, StMYC2a and StMYC2b, which are predominantly expressed in leaves and localized to the nucleus. Overexpression of StMYC2a and StMYC2b in S. tenuifolia increased the peltate glandular trichome density and monoterpenoid content. Conversely, transgenically silenced StMYC2a and StMYC2b lines had attenuated peltate glandular trichome development and reduced monoterpenoid accumulation. We further demonstrated that StMYC2a and StMYC2b directly activate two key monoterpenoid biosynthetic genes, StL3OH and StPR, by binding to G-box motifs in their promoters. Protein interaction analysis reveals that only StMYC2b physically interacts with the repressor StJAZ2, which suppresses StMYC2b-mediated transactivation, but this repression was alleviated upon stimulation with methyl jasmonate. The results revealed that the StJAZ2-StMYC2b-StL3OH/StPR functional module regulates jasmonic acid signaling-mediated glandular trichome development and monoterpenoid synthesis in S. tenuifolia. The enrichment of the transcriptional regulatory network for monoterpenoid synthesis provides a new theoretical basis for producing S. tenuifolia with high medicinal value.

Tissue culture seedlings of Bletilla striata were treated with MeJA, SA and two kinds of endophytic fungi in order to study the effects of those treatments on the physiology and total phenols content. The method of tissue culture was used to culture seeds into seedlings, and then different treatments were applied on them to observe and measure the changes of physiology and total phenols content. We find that the growth of seedlings treated with SA was poor, which treated with 40 μmol•L⁻¹ MeJA, 50 mL•L⁻¹ Hypocrea koningii and 10 mL•L⁻¹ Trichoderma koningiopsis showed better. The activity of SOD, POD and CAT was at a high level under SA treatment of each concentration. The activity of SOD and POD increased as the rise of MeJA concentration, while CAT was highest at 80 μmol•L⁻¹. The activity of SOD and POD increased with the increasing of the concentration of H. koningii treatment, while CAT reached the highest at 1 mL•L⁻¹. The activity of SOD, POD and CAT increased first and then declined with the concentration of T. koningiopsis increasing, and the highest activity was at 10 mL•L⁻¹. The contents of MDA, soluble protein and proline were increased more or less under the four treatments. The content of polysaccharide was at a high level under 60 μmol•L⁻¹ of MeJA. The total phenols content was at a high level under 40 μmol•L⁻¹ of MeJA, 60 μmol•L⁻¹ of SA, 1 mL•L⁻¹ of H. koningii and 10 mL•L⁻¹ of T. koningiopsis. The results indicated that the addition of exogenous MeJA, SA and endophytic fungi under certain concentrations could improve the resistance of B. striata and increase the content of total phenols at some degree and the trearment of MeJA, H. koningii and T. koningiopsis could promote the growth of seedlings under certain concentrations.