Studies On Assimilation Of Exogenous Nitrogen And Production Of Arginine By Arbuscular Mycorrhizal Fungus

Arbuscular mycorrhizal (AM) fungus are the most common and important endogenous mycorrhizal fungus. AM fungus establish a mutualistic symbiosis with the roots of plants, supplying the host plants with nutrient substance from the soil while taking up fixed carbons as hexose from the apoplast of the host root cortex. The extraradical mycelium (ERM) of AM fungus were able to take up and assimilate various forms of nitrogen from the surroundings. During nitrogen uptake and assimilation, most of the nitrogen will be incorporated into arginine (Arg). Arg serves as important stored and transport carrier of nitrogen in the hyphae of AM fungus. This paper established the best C, N, P concentration in the pot culture, and studied the changes of production of Arg by AM fungus under different forms of exogenous nitrogen, strains and exogenous carbon conditions respectively.The growing and propagating of AM fungi can be affected by many factors, and the most important factor is the nutrient in the pot culture. AM fungus (Glomus intraradices) was inoculated to the host plant (Allium fistulosum) and grown in pot culture. Hoagland nutrient solution was modified and the concentration of C (glucose), N (NH4NO3), P (KH2PO4) was changed. The optimum concentration of C, N, P were determined in the pot culture by measuring the rate of root infection, spores amount and dry weight of plant. The results showed that both the rate of root infection and spores amount were highest when we supplied 0.5% glucose,2 mmol/L NH4NO3,0.05 mmol/L KH2PO4 to pot culture, the host plants were growing well under this condition.The ERM of AM fungus were able to take up and assimilate various forms of exogenous nitrogen from the surroundings, and the assimilation efficiency is different. AM fungus (Glomus intraradices) was inoculated to the host plant (Allium fistulosum) and grown in three-part pot culture system, with addition of 4mmol/L different forms of exogenous nitrogen (NH4Cl, NH4NO3, KNO3, urea, glycine (Gly), arginine (Arg) and glutamine (Gln)) into the mycelium compartment. The effects of different forms of nitrogen on production of Arg by AM fungus were examined by measuring the rate of root infection, spores amount, dry weight of ERM, Arg contents in ERM and mycorrhizal roots. The results showed that the growth condition of AM fungus and the capacity of production of Arg by AM fungus were different under the different forms of exogenous nitrogen. When NH4NO3, urea and Gin as exogenous nitrogen source, the Arg content in the ERM and the total nitrogen content in shoots were higher than those exposed to other exogenous nitrogen sources; When NH4NO3, urea, Arg and Gin as exogenous nitrogen sources, Arg contents in mycorrhizal roots were in higher levels.The capacity of assimilation of exogenous nitrogen by different strains of AM fungus were different. Different strains of AM fungus (Glomus intraradices, Glomus mosseae, Glomus etunicatum, Glomus aggregatum, Acaulospora mellea) were inoculated to the host plant (Allium fistulosum) and grown in three-part pot culture system separately, with addition of 4mmol/L exogenous nitrogen (NH4Cl) into the mycelium compartment. The differences of production of Arg by different strains of AM fungus were studied by measuring the rate of root infection, spores amount, dry weight of ERM, Arg contents in ERM and mycorrhizal roots, total nitrogen in plant. The results showed that the Arg contents in ERM and mycorrhizal root of different strains of AM fungus were different. The Arg contents of Glomus intraradices and Glomus aggregatum was higher than those in others strains. The uptake of nitrogen from the medium by plants is greatly improved by mutualistic associations with AM fungus.Nitrogen metabolism was bond up with carbon metabolism in AM fungus.. AM fungi (Glomus intraradices) was inoculated to the host plant (Sorghum bicolor L. Moench) and grown in three-part pot culture system,4mmol/L NH4NO3 was added into the mycelium compartment, and different forms of carbons were added into the root compartment. The Arg and total nitrogen contents were determinated and analysed in extraradical mycelium (ERM), mycorrhizal roots and shoots separately. The aim of this research is to study the effects of different forms of external carbons on the assimilation of nitrogen and production of Arg by AM fungus. The results showed that the content of Arg in ERM and mycorrhizal roots was much higher than that in shoots; The different forms of carbon increased the dry weight of ERM and root infection rate; But glucose reduced the Arg content in ERM, mycorrhizal roots and shoots; Sucrose and glycerol had no significant effect on the production of Arg; Both external Arg and glutamine (Gln) increased the Arg content in ERM significantly; The different forms of carbon had no significant effect on total nitrogen contents in mycorrhizal roots and shoots. However the external carbon could promote the growth of AM fungus.