The Preliminary Research On Nitrate Metabolic Of Ericoid Mycorrhizae Fungus

Ericoid mycorrhizas (ERM) is a symbiotic structure between the root of several Ericaceae plants and specific soil fungi. Inoculation tests showed that mycorrhizal symbiosis can greatly promote the uptake and utilization of nitrogen by the host plants. As to Ericaceae plants, the acceleration effect is particularly notable in the nitrate condition. Therefore, further researches on ERM mycorrhizal fungi in different nitrogen forms and promotion mechanisms of mycorrhizal fungi are of great theoretical significance and applied value. The main conclusions are as follows:(1) This paper measured the mass growth、nitrogen content、activities of nitrate reductase. Results showed that ERM fungi can use various nitrogen forms, the growth of ERM fungi in nitrate and ammonium are better than that in organic nitrogen condition, Three strains have a good use of the nitrate nitrogen, and the ability of strain19is the best. The nitrate reductase activities of19in organic and nitrate nitrogen are better.(2) A subtractive cDNA library was developed to study genes associated with the nitrate-induced genes by suppression subtractive hybridization, a total of about1500subtractive positive clones of fragments are obtained. We randomly pick a300clone for sequencing, eventually won223single sequences. The sequence length is located between181bp-1007bp, and the average length is509bp. Similarity search by BLAST indicates that function known sequences are41.26%of all genes, Genes of function known primarily involves material synthesis and metabolism, energy metabolism, membrane transfer, signal transduction, transcription regulation, biological resistence and so on.(3) we detected the expression of nitrate transport and metabolic gene under different nitrogen conditions by RT PCR technology, and the results showed that the nitrate transport and metabolic gene of ERM fungi could belong to the high affinity family of nitrate transport and metabolic. And the expression of above mentioned genes can be induced by nitrate and low nitrogen conditions, be suspressed by high concentrations of ammonium.(4) When mycelia were shifted to the different time to nitrate conditions, the expression models of nitrate transporter and nitrite reductase are the same, and the expression pattern of nitrate reductase is different with them. The expression pattern of the three genes are different from the ectomycorrhizal fungi, so we speculated that they have the different model of nitrate metabolism.In conclution, ERM fungus has the strong ability to utilize nitrate is due to the related nitrate metabolism gene of ERM fungus. And the nitrate metabolism genes can be inducible expression by nitrate and low nitrogen conditions, then to generated the corresponding nitrate metabolic enzyme, with a series of enzymatic reaction, completing the nitrate absorption and utilization of ERM fungus.