Poster: Plant-symbiont interactions

Abs # 581: The forms of nitrogen taken up and transported to the Ri T-DNA carrot root by the extraradical hyphae of AM fungi

Presenter:	Jin, Hairu /, hjin@arserrc.gov
Authors	Jin, Hairu / (A)   Philip, Ppfeffer E (A)   Yair, Shachar-Hill / (B)   David, Douds D (A)   Peter, Lammers / (C)
Affiliations:	(A): United States Department of Agriculture, Eastern Regional Research Center (B): Michigan State University, Plant Biology Department (C): New Mexico State University, Department of Chemistry and Biochemistry

The forms of nitrogen taken up and transported by the extraradical hyphae of arbuscular mycorrhizal fungi in symbiosis with Ri T-DNA roots were studied. The AM fungus Glomus intraradices was grown in monoxenic culture with Ri T-DNA transformed roots in two compartment Petri dishes. Uptake from a mixture of 20 different amino acids,or tri-alanine, or bovine albumin was determined by monitoring depletion of amino acids or total N from the medium. [15N]-NH₄Cl, [15N]arginine or [U-13C6]arginine was introduced to the root-free compartment. Free amino acids of the extraradical mycelium and root compartment tissue were analyzed with GC-MS and HPLC after 4wks or 8 wks of exposure. The results indicated that the extraradical hyphae of AM fungi can utilize the soluble peptide(tri-alanine) and protein (bovine albumin); however, Phe and Tyr were not taken up. Results of exposure to [15N]NH₄Cl for 4wks clearly showed that the main free amino acid in the extraradical mycelium was arginine, which was 99% enriched in 15N. The concentration of arginine was approximately 227.93 nmol g-1 d.wt of hypha, representing more than 90% of the total nitrogen of free amino acids in the hypha. [15N]arginine or 13C6-arginine added to the fungal compartment, was observed intact in the free amino acids of the root compartment tissue. This indicated that arginine can be taken up directly by extraradical hyphae and transported to the root compartment tissue. However, compared to ammonium, arginine was not easily taken up by the AM fungi. Nevertheless, large amounts of arginine were synthesized by the extraradical hyphae and transported to the root compartment.Thus, arginine is one major form of nitrogen stored and transported to the root host by the extraradical hypha of AM fungi.