Study On The Interaction Mechanism Between Endophytic Fungi And Its Host Plants In

Atractylodes lancea is a Chinese traditional medicinal plant widely distributed in China. Its volatile oil shows a wide range of antifungal activities, and is used as a main medicinal ingredient. However, the natural resources of A. lancea have been sharply decreased due to a variety of predatory exploitation. Currently, most herbs traded on the market are artificially cultivated. A key question is that how the quality of the herbs can be ensured or even improved when they are cultivated away from their native environment. In order to utilize the endophyte resources and improve the quality of the cultivated herbs, various methods, including microbiology and biotechnology of plant, were used to investigate interactions between endophytic fungi and their host plantlets.First of all, in order to investigate the inhibitory effect of host plants secondary metabolite on the growth of endophytic and exogenous fungi, the volatile oil from medicinal plant A. lancea was extracted with organic solvent extraction method, and its antimicrobial activity against three species of endophytic and seven species of exogenous fungi was determined by paper disc assay and spread-plate. The volatile oil had inhibitory effects on the growth of test endophytic fungi. It had strong antimicrobial effect against Rhodotorual glutinis and Saprolegnia ferax, but weak effect against Rhizopus sp. and Absidia sp.. It suppressed the sporulation of Trichoderma viride and Aspergillus niger, but no effects on the growth of Phytophthora. Under the stress of high concentrations of volatile oil, the hyphal branches of test endophytic fungi were increased, the distance between branches became shorter and the growth of aerial hyphae was inhibited. The test endophytic fungi had remarkable ability to metabolize and transform the volatile oil, and decrease the contents of its main ingredients. All the results showed that the volatile oil extracted from A. lancea had inhibitory effect on the growth of endophytic fungi, and the fungi could adapt to the volatile oil via metabolizing and decomposing it.After that, to effectively utilize endophytic fungus and its elicitor resources, the effects of endophytic fungus Gilmaniella sp. (AL12) and its elicitor on the defense and metabolic responses of host plants Atractylodes lancea were investigated. The results showed that the promotion effect of the fungus to the growth of host plantlets was much better than its elicitor. The fungus could establish stable symbiotic relationship with the host. Both fungus and elicitor enhanced defense-related enzymes activities. In fungus-inoculated groups, phenylalnine ammonialyase (PAL) and polyphenoloxidase (PPO) activities increased slowly, and reached the maximum level during the later stage, whereas peroxidase (POD) activity peaked in the first few days. Additionally, the activities of chitinase andβ-1,3-glucanases were significantly higher than those of the control. In elicitor-treated groups, however, most of the enzymes were activated during the early stage, and their highest levels were generally lower than those of the fungus-inoculated groups. Compared with the elicitor, fungal infection could improve the photosynthetic rate of the host, and increase carbohydrate levels as well as chlorophyll contents in host leaves. The total content of the four main components of volatile oil was also increased in elicitor-treated groups, but there was no particular pattern in the increase. Meanwhile, in the fungus-inoculated groups, the content of atractylone significantly increased with time, while the content ofβ-eudesmol decreased. These results indicated that fungal eliciror could substantially improve the total content of volatile oil, while the fungus could more effectively enhance the quality of the herbal medicines.Inoculation with endophytic fungus AL12 induced multiple responses in host plantlets of A. lancea, including the burst of NO, SA, H2O2, and the accumulation of volatile oil. In order to investigate the pathways that the three signal molecules affect the volatile oil production, the plantlets were treated with NO specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxi-de potassium salt (cPTIO), SA synthesis inhibitor trans-cinnamic acid (trans-CA), membrane NADPH oxidase inhibitor diphenylene iodonium (DPI) and catalase (CAT). The results showed pretreatment of plantlets with cPTIO, DPI/CAT and trans-CA inhibited the burst of signal molecules and volatile oil accumulation induced by the fungus. Exogenous NO donor SNP could promote SA and H2O2 production as well as volatile oil accumulation. Combined application of trans-CA and DPI/CAT could inhibit the promotion effects of exogenous NO. Exogenous SA and H2O2 had no effects on NO production, but they could reverse the total inhibitory effects of cPTIO, CAT/DPI and trans-CA toward volatile oil accumulation. Exogenous H2O2 had promotion effect on SA production, yet CAT/DPI could not significantly prevent SA synthesis. These data indicated NO mediates violate oil accumulation induced by the fungus through SA and H2O2 dependent pathways. H2O2 can regulate SA production, but does not act as upstream signal molecule.