IAA and ZR content in leek (Allium porrum L.), as influenced by P nutrition and arbuscular mycorrhizae, in relation to plant development

Leek plants (Allium porrum L.), infected or not with the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, were grown in a sand-hydroponic system, fed with a nutrient solution containing 3.2 or 96 μM P and analyzed for root IAA and ZR content, to assess the role played by the fungus and P nutrition on host hormonal balance. IAA was analyzed by HPLC-fluorimetry, ZR by HPLC-UV coupled with a bioassay based on the expression of a phytohormone-regulated GUS reporter gene. Shoot and root weights and shoot FW-DW ratio enhancements, as well as root-to-shoot DW ratio decrement in mycorrhizal plants, were related to P nutrition. Shoot P concentration was increased by mycorrhizae at both P levels, but was comparable in AM plants grown at 3.2 μM P and non mycorrhizal (NM) plants at 96 μM P. Mycorrhizae and P increased IAA at substantially similar values, while P increased ZR much more than mycorrhizae did. These results are discussed in relation to root architecture modifications induced by the AM fungus.