Etude du comportement de Gentiana lutea L. en conditions contrôlées

National audienc

The Arum-Paris continuum of mycorrhizal symbioses

The definitive version may be found at www.wiley.com•  A survey of 12 plants colonized by six species of arbuscular mycorrhizal fungi was conducted to explore the diversity of Arum and Paris mycorrhizal structures. •  Surveyed root material was sectioned both longitudinally and transversely, double-stained and mycorrhizal structures were identified. A detailed time course experiment using four plant, and four fungal species, was used to investigate the sequential development of hyphae, arbuscules, hyphal coils, arbusculate coils and vesicles. •  The survey indicated that there was a continuum of mycorrhizal structures ranging from Arum to Paris, depending upon both the host plant and the fungus. The time course showed that total colonization increased, and that the establishment of the various mycorrhizal structures did not appear to change greatly over time. •  It was concluded that identification of fungal structures and their subsequent development into morphological types is not easily defined. Visual inspection of root squashes is not always adequate, especially where transverse sections are needed to determine if longitudinal hyphae are inter or intracellular; this is essential to distinguish intermediate types.S. Dickso

Identification of mycorrhiza-regulated genes with arbuscule development-related expression profile

Grunwald U, Nyamsuren O, Tarnasloukht M, et al. Identification of mycorrhiza-regulated genes with arbuscule development-related expression profile. PLANT MOLECULAR BIOLOGY. 2004;55(4):553-566.Suppressive subtractive hybridisation was applied to the analysis of late stage arbuscular mycorrhizal development in pea. 96 cDNA clones were amplified and 8 1, which carried fragments more than 200 nt in size, were sequence analysed. Among 67 unique fragments, 10 showed no homology and 10 were similar to sequences with unknown function. RNA accumulation of the corresponding 67 genes was analysed by hybridisation of macro-arrays. The cDNAs used as probes were derived from roots of wild type and late mutant pea genotypes, inoculated or not with the AM fungus Glomus mosseae. After calibration, a more than 2.5-fold mycorrhiza-induced RNA accumulation was detected in two independent experiments in the wild type for 25 genes, 22 of which seemed to be induced specifically during late stage AM development. Differential expression for 7 genes was confirmed by RT-PCR using RNA from mycorrhiza and from controls of a different pea cultivar. In order to confirm arbuscule-related expression, the Medicago truncatula EST data base was screened for homologous sequences with putative mycorrhiza-related expression and among a number of sequences with significant similarities, a family of trypsin inhibitor genes could be identified. Mycorrhiza-induced RNA accumulation was verified for five members by real-time PCR and arbuscule-related activation of the promoter could be shown in transgenic roots for one of the genes, MtTi1

Structural differences in arbuscular mycorrhizal symbioses: more than 100 years after Gallaud where next?

The original publication can be found at www.springerlink.comThis review commemorates and examines the significance of the work of Isobel Gallaud more than 100 years ago that first established the existence of distinct structural classes (Arum-type and Paris-type) within arbuscular mycorrhizal (AM) symbioses. We add new information from recent publications to the previous data last collated 10 years ago to consider whether any patterns have emerged on the basis of different fungal morphology within plant species or families. We discuss: (1) possible control exerted by the fungus over AM morphology; (2) apparent lack of plant phylogenetic relationships between the classes; (3) functions of the interfaces in different structural classes in relation to nutrient transfer in particular; and (4) the occurrence of plants with both of the major classes, and with intermediate AM structures, in different plant habitats. We also give suggestions for future research to help remove uncertainties about the functional and ecological significance of differences in AM morphology. Lastly, we urge retention of the terms Arum- and Paris-type, which are now well recognised by those who study AM symbioses. Electronic supplementary material The online version of this article (doi:10.1007/s00572-007-0130-9) contains supplementary material, which is available to authorized users.S. Dickson, F. A. Smith and S. E. Smit