Désiré-Georges Strullu

In vitro mass-production of the arbuscular mycorrhizal fungus, Glomus versiforme, associated with Ri T-DNA transformed carrot roots

The rate of in vitro spore formation of the arbuscular mycorrhizal fungus Glomus versiforme was followed in Petri dishes, using mycorrhizal root-segment inoculum associated with Ri T-DNA transformed carrot roots. Three phases of sporulation were observed: a lag phase, a period of intensive spore production and a plateau phase. An average of 9500 spores per Petri dish was produced after 5 months of dual culture. The root-organ culture system supported extensive root colonization, with many arbuscules and vesicles being formed. The fungus, both within root-segments and as spores produced, was viable and able to complete its life cycle in vitro. The mycorrhizal root-segments, however, exhibited higher inoculum potential due to the numerous vesicles and extensive intraradical mycelium.

Dual axenic culture of sheared-root inocula of vesicular-arbuscular mycorrhizal fungi associated with tomato roots

Surface-sterilized sheared-root inocula of two vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus intraradices and G. versiforme) from pot cultures associated with excised tomato roots showed significant sporulation and the production of an extensive hyphal biomass. As many as 102–103 axenic mature spores were recovered in Petri dishes during 3 months incubation in the dark. Propagules of both species were able to complete their vegetative life cycle in vitro and efficiently colonize Acacia albida roots after 1 month under greenhouse conditions. The effectiveness of 0.5 cm pieces of VAM roots as starter inocula indicates the high inoculum potential of intravesicle propagules.

Methodologies for in Vitro Cultivation of Arbuscular Mycorrhizal Fungi with Root Organs

Themonoxenic cultureof arbuscularmycorrhizal (AM) fungi hasmarkedly improved our understanding of the symbiosis. In the past 15 years, increasing amounts of literature have been devoted to this intimate plant–fungal association using various AM fungi in vitro cultivation systems, with different hosts, AM fungal propagules and growth media. The proportion of papers published using either in vitro, axenic, monoxenic, root organ culture or ROC as keywords, relative to the overall literature dealing with AM fungi (ISI web of Science http://www.isinet.com)4, was less than 1% in the years 1987–1989, increasing to approximately 5% in the subsequent 6 years (1990–1995), to reach a plateau at 8% from 1996 to present. The invariable proportion between papers using AM fungi in vitro systems and complete literature on AM fungi since 1996 until today suggests that the use of this system still remains in the hands of a limited number of researchers, and that new progress is necessary to reach a broader audience. If one agrees that the axenic culture of AM fungi remains the major challenge at the start of this new millennium, the present diffusion of clear protocols on AM fungi in vitro culture techniques may render this technology more widely accessible and secure its broad and reliable dissemination. Indeed, as stated byBago andCano (seeChap. 7) . . . “AM(fungi)monoxenics are far

Evidence of parasitic Oomycetes (Peronosporomycetes) infecting the stem cortex of the Carboniferous seed fern Lyginopteris oldhamia

Thin sections of petrified fossils made during the latter part of the nineteenth and early twentieth centuries to investigate the internal tissue systems of plants now provide an important new source of information on associated micro-organisms. We report a new heterokont eukaryote (Combresomyces williamsonii sp. nov.) based on exquisitely preserved fossil oogonia, antheridia and hyphae from the Carboniferous (Pennsylvanian: Bashkirian stage) of UK. The structure of the oogonia and antheridia and features observed within the hyphae demonstrate a relationship with Oomycetes (Peronosporomycetes). The fossil micro-organism was documented in situ in petrified stem cortex and rootlets of the extinct seed fern Lyginopteris oldhamia (Pteridospermales). The main observed features point towards a pythiaceous Oomycete but links to biotrophic Albuginales or Peronosporaceae cannot be ruled out owing to the observation of a possible haustorium. Our study provides the earliest evidence for parasitism in Oomycetes.

The entrapment of Glomus sp. in alginate beads and their use as root inoculum.

Intraradical forms of Glomus sp. (vesicles and mycelium fragments) were entrapped in alginate and used as inoculum. Isolated intraradical material was found to regenerate in alginate beads and the regenerated mycelium infected roots under controlled conditions. Storage at 4 °C for one month did not limit the hyphal regeneration and the formation of mycorrhizas.

Expression of a Bet v 1 homologue gene encoding a PR 10 protein in birch roots: induction by auxin and localization of the transcripts by in situ hybridization

In birch roots (Betula pendula Roth), two members of the Bet v 1 gene family which encode PR 10 proteins have previously been characterized. One of these members, named Bet v 1-sc1, is significantly induced in response to biotic or abiotic factors. We have analysed the expression of Bet v 1-sc1 in birch roots treated either with 1 M indole-3-acetic acid (IAA) or 1 M kinetin using reverse transcription–polymerase chain reaction (RT–PCR), northern blotting and competitive PCR. High accumulation of the Bet v 1-sc1 transcripts was recorded only after auxin application, while kinetin had no effect. By in situ hybridization, we have investigated the localization of Bet v 1-sc1 mRNA in birch roots after induction of the gene by root treatment with 1 M IAA. Using root tip sections, we showed that Bet v 1-sc1 is significantly expressed in the apical meristem and the procambium. In sections taken in the zone producing lateral roots, the presence of Bet v 1-sc1 was found at sites of emerging secondary root primordia. This first report of localization of Bet v 1-sc1 expression suggests that this gene could be involved in the processes leading to lateral root initiation.

The first record of mycorrhizae on sub-Antarctic Heard Island: a preliminary examination

Roots of nine of the 12 vascular plant species present on sub-Antarctic Heard Island were examined for mycorrhizae. All species examined had some type of mycorrhization with most possessing associations with vesicular-arbuscular mycorrhizae or dark septate mycorrhizae. The degree of mycorrhization varied considerably across sites. Sampled plants were growing on either morainic or beach substrates with some areas exposed only in the last century. As mycorrhizae are known to play an important role in the nutrient uptake by host-plants, these results support the idea that mycorrhizae can influence the capacities of plants to colonize in cold and low-nutrient environments such as sub-Antarctic glacier forelands. Comparisons with data from other sub-Antarctic islands are made.

The early land plants from the Armorican Massif: sedimentological and palynological considerations on age and environment

The Châteaupanne Unit belongs to the South Armorican domain of the Armorican Massif (France), which is part of the Variscan belt. This unit includes two Lower Devonian plant levels and one of them corresponds to the Basal Member of the Chalonnes Formation. A sedimentological and palaeontological analysis of these fossiliferous deposits from the Châteaupanne quarry (Montjean/Loire, Maine et Loire, France) is presented here for the first time. The age determination based on palynology indicates that the locality records the earliest occurrence of plant megafossils in the Armorican Massif. Their presence suggests an emergence event that has never been described before. Our study highlights the promising potential of the Basal Member of the Chalonnes Formation to aid in understanding these occurrences, and provides new insights into the history of the Variscan belt.

Protein biosynthesis changes during mycorrhiza formation in roots of micropropagated birch

Summary Birch (Betula pendula Roth) micropropagated plantlets were inoculated with 7 different isolates of the mycorrhizal fungus Paxillus involutus Batsch. Based on the level of fungal ergosterol measured in roots at the end of the “mycorrhiza formation stage”, strain P0 was chosen as the reference strain. Electrophoretic analysis of in vivo labeled proteins extracted from mycorrhizal roots 96 h post-inoculation with this strain, noninoculated roots, and free-living mycelium, revealed that specific polypeptides were synthesized during ectomycorrhiza formation. To examine hypothetical similarity between some of these polypeptides and defense proteins, parts of corresponding putative genes of birch were isolated. Partial sequencing of one clone have shown that it contained a portion of the gene for phenylalanine ammonialyase.

Première contribution à l'étude des mycorhizes des îles Kerguelen

Abstract Until recently mycorrhizae had not been studied in the Antarctic region. Some studies have demonstrated that mycorrhizae occur in some southern circumpolar islands. This paper gives the first results on the mycorrhizae in the Kerguelen islands (Sub-antarctic). Twenty-one plant root systems, fixed in the field, were examined microscopically in the laboratory to determine their mycorrhizal status. No ectomycorrhiza, arbutoid or ericoid were noted. Six plant species showed vesicular arbuscular mycorrhizae: Ranunculus biternatus, Galium antarcticum, Festuca erecta, Poa kerguelensis, Agrostis magellanica and Poa annua. However, the mycorrhizal status varied according to the site studied.