© 2005 Heron Publishing—Victoria, Canada
Shoot water status and ABA responses of transgenic hybrid larch Larix kaempferi × L. decidua to ectomycorrhizal fungi and osmotic stress
Ana Rincón (1), Outi Priha (1), Marie-Anne Lelu-Walter (2), Magda Bonnet (3), Bruno Sotta (3) and François Le Tacon (1, 4)
1. Unité Mixte de Recherches 1136, Interactions Arbres-Microorganismes, INRA Centre de Nancy, 54280 Champenoux, France / 2. UR 588, Unité Amélioration, Génétique et Physiologie Forestières (UAGPF), Équipe C.A.M.B.I.U.M., INRA, Centre de Recherches
d’Orléans, avenue de la Pomme de Pin, Ardon, BP 206 19, 45166 Olivet cedex, France / 3. Laboratoire de Physiologie Cellulaire et Moléculaire des Plantes, UMR CNRS 7632, Université Pierre et Marie Curie, le Raphaël,
3 rue Galilée, 94200 Ivry sur Seine, France / 4. Corresponding author (le_tacon@nancy.inra.fr) / Received August 16, 2004; accepted January 15, 2005; published online July 4, 2005
Summary
It has been postulated that osmotic effects on plant tissue are mediated by abscisic acid (ABA). Hybrid larch (Larix kaempferi (Lambert) Carr. × L. decidua Mill.) plantlets, transformed with the ABA-inducible wheat Em promoter associated with the Gus reporter gene, were axenically inoculated with two ectomycorrhizal fungi: Cenococcum geophilum Fr., considered tolerant to water stress, and Laccaria bicolor (Marie) Orton, considered less tolerant to drought. The mycorrhizal and non-mycorrhizal transgenic plantlets were subjected
to osmotic stress by adding polyethylene glycol (PEG) to the culture medium. In the presence of PEG, L. bicolor and C. geophilum reduced shoot water potential and turgor potential, but increased host osmotic potential. Treatment of plantlets with PEG
induced a significant increase in endogenous ABA concentrations. Laccaria bicolor and C. geophilum behaved similarly and significantly decreased the ABA response of plantlets to PEG treatment. Moreover, inoculation with
either fungus regulated the ABA response of the plantlets even when the fungus was separated from the host by a cellophane
sheet that prevented mycorrhiza formation. Although the wheat Em promoter was inducible in larch plantlets, it was not regulated by endogenous ABA. Induction of the wheat Em promoter in larch plantlets depended on organ type, with maximum induction in the root apex. Induction of the Em promoter was significantly decreased by mycorrhizal inoculation.
Keywords:
Cenococcum geophilum, Em promoter, GUS activity, Laccaria bicolor, osmotic potential, water potential.
