RESUMO
Endophytic fungi can promote host plant growth, enhance antioxidant defense enzyme activity, and induce the biosynthesis and accumulation of secondarymetabolites. Therefore, using endophytic fungi to improve the quality and yield of medicinal plants or important crops is an effective means of regulation. Colletotrichum sp. AP12 has been reported to produce andrographolide compounds (ADCs). This study aimed to investigate the effects of AP12 and its elicitors on the growth, defense enzyme activity, accumulation, and transcription levels of key genes in Andrographis paniculata (Burm. f.) Nees (A. paniculata). Using fermentation method to prepare AP12 into the inactivated fermentation solution (IFS), fermentation solution (FS), inactivated mycelium solution (IMS), and mycelium solution (MS), and the results showed that all four fungal elicitor components (ECs) could promote A. paniculata growth, enhance antioxidant defense enzymes, and increase ADC content and yield, especially the IMS group that had the highest leaf area, whole plant dry weight, superoxide dismutase (SOD), catalase (CAT) enzyme activities, total lactone contents, and yields, which were 2.37-, 1.60-, 2.20-, 3.27-, 1.59-, and 2.65-fold of the control, respectively. The 14-deoxyandrographolide (NAD) in the host irrigated with MS was 3.35-fold that of the control. In addition, AP12-infected A. paniculata sterile seedlings could significantly increase ADC content and expression levels of key enzyme genes, especially on day 12, when the total lactone content of the host reached 88.881± 5.793 mg/g DW, while on day 6, CPS gene expression level reached 10.79-fold that of the control, in turn promoting the biosynthesis and accumulation of andrographolide. In conclusion, the endophytic fungus AP12 is beneficial to the growth and secondary metabolism of A. paniculata, which is helpful for the cultivation and application of the biological bacterial fertilizer in A. paniculata, providing a theoretical and research basis for the use of endophytic fungi as a microbial resource to improve the quality and yield of medicinal plants.
RESUMO
Endophytic fungi of medicinal plants are abundant, and their metabolites often have antioxidant, antibacterial, and antitumor effects and can produce secondary metabolites identical or similar to those of their hosts, which can mitigate the problem of insufficient supply of medicinal plants. In this study, we screened endophytic fungi for strains that produce the same diterpene lactones as Andrographis paniculata based on their biological activity. Firstly, the dominant group of endophytic fungi of Andrographis paniculata was screened and pathogenicity was studied using Koch's rule. Secondly, DPPH, ABTS, OH, PTIO radical scavenging, and FRAP assays were used to detect the antioxidant activity of the extracellular extracts of the strains, and total phenol and total flavonoid contents of the strains with high antioxidant capacity were determined. S. aureus, B. subtilis, E. coli, and P. aeruginosa were used to determine the antibacterial activity of the mycelial extracts of the strains. Finally, the secondary metabolites of the mycelial extracts of the strains were examined by high-performance liquid chromatography. The results showed that 32 strains of Andrographis paniculata were relatively isolated > 70% and non-pathogenic. Extracellular extracts of strains AP-1 and AP-4 showed vigorous antioxidant activity, and AP-4, AP-12, AP-47, and AP-48 showed antibacterial activity against four strains of bacteria. The HPLC results indicated that the mycelial extracts of AP-4 and AP-12 contained diterpene lactones. The two endophytic fungi were recognized as Colletotrichum sp. The study successfully obtained diterpene lactones from the endophytic fungus of Andrographis paniculata and confirmed the feasibility of using endophytic fungal strains to produce active substances consistent with the host. It was also useful for exploring endophytic fungi and medicinal plants. The relationship provides theoretical guidance.