Arbuscular mycorrhizal （AM） fungi are obligate symbionts that colonize the roots of more than 80% of land plants. Experi- ments on the relationship between the host plant and AM in soil or in sterile root-organ cult...Arbuscular mycorrhizal （AM） fungi are obligate symbionts that colonize the roots of more than 80% of land plants. Experi- ments on the relationship between the host plant and AM in soil or in sterile root-organ culture have provided clear evidence that the extraradical mycelia of AM fungi uptake various forms of nitrogen （N） and transport the assimilated N to the roots of the host plant. However, the uptake mechanisms of various forms of N and its translocation and transfer from the fungus to the host are virtually unknown. Therefore, there is a dearth of integrated models describing the movement of N through the AM fungal hyphae. Recent studies examined Ri T-DNA-transformed carrot roots colonized with AM fungi in ~SN tracer experi- ments. In these experiments, the activities of key enzymes were determined, and expressions of genes related to N assimilation and translocation pathways were quantified. This review summarizes and discusses the results of recent research on the forms of N uptake, transport, degradation, and transfer to the roots of the host plant and the underlying mechanisms, as well as re- search on the forms of N and carbon used by germinating spores and their effects on amino acid metabolism. Finally, a path- way model summarizing the entire mechanism of N metabolism in AM fungi is outlined.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 30970101)
文摘Arbuscular mycorrhizal （AM） fungi are obligate symbionts that colonize the roots of more than 80% of land plants. Experi- ments on the relationship between the host plant and AM in soil or in sterile root-organ culture have provided clear evidence that the extraradical mycelia of AM fungi uptake various forms of nitrogen （N） and transport the assimilated N to the roots of the host plant. However, the uptake mechanisms of various forms of N and its translocation and transfer from the fungus to the host are virtually unknown. Therefore, there is a dearth of integrated models describing the movement of N through the AM fungal hyphae. Recent studies examined Ri T-DNA-transformed carrot roots colonized with AM fungi in ~SN tracer experi- ments. In these experiments, the activities of key enzymes were determined, and expressions of genes related to N assimilation and translocation pathways were quantified. This review summarizes and discusses the results of recent research on the forms of N uptake, transport, degradation, and transfer to the roots of the host plant and the underlying mechanisms, as well as re- search on the forms of N and carbon used by germinating spores and their effects on amino acid metabolism. Finally, a path- way model summarizing the entire mechanism of N metabolism in AM fungi is outlined.
