Cellular interactions between G. mosseae and a Myc^-1Nod^- mutant in Medicago truncatula

CALANTZIS, CATHERINE¹, DOMINIQUE MORANDI² & VIVIENNE GIANINAZZI-PEARSON².

¹Laboratoire de Bioenergetique, Station Botanique, Geneva University, 1254 Lullier/Jussy, SWITZERLAND. ²Laboratoire de Phytoparasitologie INRA/CNRS, CMSE-INRA, BV 1540, 21034 Dijon Cedex, FRANCE.

Medicago truncatula, as nearly all legumes, forms two types of root symbiosis, nitrogen-fixing nodules and endomycorrhiza. Cellular interactions with arbuscular mycorrhizal fungi result in intense colonisation of parenchymal cortical cells, with the formation of a fungal haustorium, the arbuscule, and differentiation of a symbiotic interface essential to nutrient exchange between plant and fungal cells. Symbiosis-defective (Myc^-1 Nod^-) mutants have been obtained in Medicago truncatula which are characterised by resistance to both arbuscular mycorrhizal fungi and Rhizobium melilotii (Sagan et al., 1995). Incompatibility towards Glomus mosseae (BEG 12) in one mutant (TR26) is associated with (i) abnormal plant wall reactions characterised by an autofluorescent apposition layer within cells adjacent to fungal hyphae, (ii) pectin-rich material is deposited between plant and fungal walls and (iii) disorganisation of fungal hyphae in contact with root cells. No callose accumulation is observed. The mutation therefore appears to affect fungal-root interactions in a different way to in pea Myc^-1Nod^- mutants (Gollotte et al., 1993).

Sagan et al. (1995) Plant Sci.111, 63-71 ; Gollotte et al. (1993) Planta191, 112- 122.

Key words: M. truncatula - mutants - G. mosseae - cellular incompatibility