© 2003 Heron Publishing—Victoria, Canada
Comparative effects of auxin transport inhibitors on rhizogenesis and mycorrhizal establishment of spruce seedlings inoculated
with Laccaria bicolor
Ana Rincón (1), Outi Priha (1), Bruno Sotta (2), Magda Bonnet (2) and François Le Tacon (1, 3)
1. Unité Mixte de Recherches Interactions Arbres-Microorganismes, INRA Centre de Nancy, 54280 Champenoux, France / 2. UMR de Physiologie Cellulaire et Moléculaire des Plantes, CNRS et Université PARIS VI, 4 place Jussieu, Tour 53, 75005 Paris,
France / 3. Author to whom correspondence should be addressed (le_tacon@nancy.inra.fr) / Received April 10, 2002; accepted January 11, 2003; published online July 1, 2003
Summary
We compared the effects of two auxin transport inhibitors (2,3,5-triiodobenzoic acid (TIBA) and 1-N-naphthylphthalamic acid (NPA)) on rhizogenesis and mycorrhizal establishment of Picea abies L. (Karst.) seedlings inoculated with Laccaria bicolor S238N (Maire) Orton. Inoculation of seedlings with L. bicolor under in vitro conditions strongly increased host root and shoot growth. Although TIBA had no effect on taproot growth, NPA
decreased taproot growth and deformed the root apex into a globular shape in both non-inoculated seedlings and seedlings inoculated
with L. bicolor. Inoculation with L. bicolor strongly increased lateral rhizogenesis of the seedlings, and application of 100 µM indole-3-acetic acid (IAA) partially
reproduced this effect. Although TIBA completely inhibited the stimulatory effect of L. bicolor on lateral root formation, NPA inhibited it only partially. Both TIBA and NPA counteracted the effect of exogenous IAA on
lateral rhizogenesis. Inoculation with L. bicolor significantly increased shoot growth and seedling dry biomass, whereas application of exogenous IAA had no effect on either
parameter. There was no effect of NPA on shoot growth and biomass production. The presence of TIBA completely prevented the
development of ectomycorrhizal structures (mantle and Hartig net). In the presence of NPA, the number of seedlings colonized
by the fungus was reduced and the degree of development of ectomycorrhizal structures was variable, but not completely prevented.
In medium lacking tryptophan, neither TIBA nor NPA inhibited the release of IAA produced by L. bicolor in pure culture. When 100 µM tryptophan was added to the medium, TIBA significantly increased the amount of IAA released
by the fungus, whereas NPA had no significant effect. We conclude that fungal IAA plays an important role in plant rhizogenesis
and in the establishment of ectomycorrhizal symbiosis.
Keywords:
ectomycorrhizas, NPA, TIBA.
