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 mycorrh izal (AM) fungus, Glomus mosseae, were grown in a sand-hydroponic system, f ed with a nutrient solution containing 3.2 or 96 muM P and analyzed for roo t IAA and ZR content, to assess the role played by the fungus and P nutriti on on host hormonal balance. IAA was analyzed by HPLC-fluorimetry, ZR by HP LC-UV coupled with a bioassay based on the expression of a phytohormone-reg ulated GUS reporter gene. Shoot and root weights and shoot FW-DW ratio enha ncements, as well as root-to-shoot DW ratio decrement in mycorrhizal plants , were related to P nutrition. Shoot P concentration was increased by mycor rhizae at both P levels, but was comparable in AM plants grown at 3.2 muM P and non mycorrhizal (NM) plants at 96 muM P. Mycorrhizae and P increased I AA at substantially similar values, while P increased ZR much more than myc orrhizae did. These results are discussed in relation to root architecture modifications induced by the AM fungus.