Intracellular pH in Arbuscular Mycorrhizal Fungi1
A Symbiotic Physiological Marker
Mario Jolicoeur,
Sophie Germette,
Martin Gaudette,
Michel Perrier, and
Guillaume Bécard*
BIOPRO Research Center, École Polytechnique de
Montréal, Chemical Engineering Department, 2900 Édouard-Montpetit, Montréal, Québec, Canada, C.P.
6079, H3C 3A7 (M.J., M.G., M.P.); and Laboratoire de Mycologie
Végétale, Université Paul-Sabatier, 118 route de
Narbonne, 31062 Toulouse, France (M.J., S.G., G.B.)
A method was developed to perform
real-time analysis of cytosolic pH of arbuscular mycorrhizal fungi in
culture using dye and ratiometric measurements (490/450 nm
excitations). The study was mainly performed using photometric
analysis, although some data were confirmed using image analysis. The
use of nigericin allowed an in vivo calibration. Experimental
parameters such as loading time and concentration of the dye were
determined so that pH measurements could be made for a steady-state
period on viable cells. A characteristic pH profile was observed along
hyphae. For Gigaspora margarita, the pH of the tip (0-2
µm) was typically 6.7, increased sharply to 7.0 behind this region
(9.5 µm), and decreased over the next 250 µm to a constant value of
6.6. A similar pattern was obtained for Glomus
intraradices. The pH profile of G. margarita
germ tubes was higher when cultured in the presence of carrot
(Daucus carota) hairy roots (nonmycorrhizal). Similarly, extraradical hyphae of G. intraradices had a higher
apical pH than the germ tubes. The use of a paper layer to prevent the
mycorrhizal roots from being in direct contact with the medium selected
hyphae with an even higher cytosolic pH. Results suggest that this
method could be useful as a bioassay for studying signal perception
and/or H+ cotransport of nutrients by arbuscular
mycorrhizal hyphae.
1
Scholarships to M.J. and M.G. supporting their
stay in Toulouse were provided by the Fonds pour la formation de
Chercheurs et l'Aide à la Recherche (contract no. 94-CI-0117),
and the Conseil Régional de Midi-Pyrénée (contract
no. 9300417) funded the spectrofluorometric microscope used in this
study.
*
Corresponding author; e-mail becard{at}cict.fr; fax
33-5-61-55-62-10.
Plant Physiol. (1998) 116: 1279-1288
Copyright Clearance Center: 0032-0889/98/116/1279/10
© 1998 American Society of Plant Physiologists