| Nematode predate on many crops worldwide, and have caused the greatest economic losses every year. Nematode-trapping fungi are natural enemies of nematodes and are considered as ideal agents for controlling parasitic nematodes of plants and animals. Among them, Arthrobotrys oligospora is one of the most common and well-studied nematode-trapping fungi that can form adhesive network traps and be found in diverse soil environments. Many inducers such as living nematode, some small peptides and amino acids, plant pheromones abscisic acid, nematodes quorum sensing molecule glycosides, soil bacteria and nitrate have reported to affect trap formation in Arthrobotrys oligospora. Ammonia secreted by living nematode have hypothesized to involved in trap formation in Arthrobotrys oligospora. Urea metabolite ammonia functions as signal molecule to induce trap formation in Arthrobotrys oligospora. In fact, many fungi can produce ammonia and it has ability to alkalinize the extracellular milieu. The roles suggested for ammonia produced by fungi was that it could affect fungal morphogenesis and pathogenicity. Four key genes pacC, areA,amet and mep, and amino acid metabolic pathway are associated with ammonia metabolism. However, there is no report about the role of ammonia and ambient pH in A. oligospora trap formation by other inducers.In this study, trap formation in A. oligospora induced by nematode extract, amino acids, nitrate or bacteria was analyzed by Nessler’s reagent and ammonium test kit. The role of ammonia and ambient pH was also studied. The conclusions are shown in following:1. Among the inducers, ammonia secretion was only associated with trap formation in A. oligosporaby nematode extracts and ammonia concentration presented a trend of increase after a reduction.2. Trap formation in A. oligospora by different concentration ammonia was studied.The results showed that A. oligospora formed traps by ammoniaat concentration of 0.1 mM, and maximumnumber of traps were formed at optimal concentration of 0.2 mM. Then number of traps reduced With the increase of ammonia concentrationand trap formation was repressed at concentration of 10 mM. It indicated that trap formation in A. oligospora could be induced at concentration of ammonia secreted during trap formation in A. oligospora induced by nematode extract.3. Ambient pH was measured with a micro-combination pH electrode and bromocresol purple, and found that pH in medium increased after a reduction during trap formation in A. oligosporainduced by nematode extract. The change of pH intternal hyphae was suty by fluorescent dye BCECF-AM and found that the pH of the internal hyphae reduced after a rise during trap formation in A. oligospora induced by nematode extract.4. Four genes pacC、mep、amet and areA inA. oligospora mycelia were analyzed using real-time qPCR, and the results suggested that the expression level of amet gene during trap formation in A. oligospora induced by nematode extract was higher than that in control. Based on the above results, We hypothesized that increase of ammonia concentration during trap formation in A. oligosporainduced by nematode extract was related to up-regulated expression of amet gene.5. Number of traps in A. oligospora induced by nematode extract was related to medium initial pH and buffer capacity of the medium.6. Ammonia concentration during trap formation indued by nematode extract in different initial pH was quantified and the results showed that the concentration of ammonia produced in A. oligospora induced by nematode extract was related to medium initial pH.Highlights of this research:1. Arthrobotrys oligospora can secrete ammonia and increase medium pH during trap formationindued by nematode extract.2. The medium initial pH affect trap formation in A. oligospora by nematode extract. Ammonia accumulation and trap formation in A. oligospora by nematode extract were related to medium initial pH... |
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