Nitrogen transfer and assimilation in a mycorrhizal in vitro root culture system.

Abstract

The present study aimed to determine the effect of arbuscular mycorrhizal (AM) symbiosis on plant nitrogen (N) nutrition. Previous studies had shown, mainly from soil experiments, the ability of AM fungi in their N uptake and transfer to host plants. These results led us to postulate that AM fungi contribute to enhance the activity of N-assimilating enzymes in host roots, and possess their own N-metabolic system. To investigate this, N key-enzyme activities were examined in Ri T-DNA carrot (Daucus carota L.) roots, grown into an in vitro system, with or without the AM fungus, Glomus intraradices Schenck & Smith. Such a system allowed us to grow and maintain an experimental model of intact roots-AM fungus, in a controlled and pathogen-free environment. Total carbon (C) and N contents had been quantified by Elemental Analysis in AM and non-AM roots and in the mycelium. By Mass Spectrometry, the uptake and transfer of labelled nitrogen (15N) from the fungal mycelium to AM roots, as well as in the non-AM roots, were also determined. Finally, some of the N-assimilating enzymes were characterized by immunodetection (Western blot). (Abstract shortened by UMI.)