Some ultrastructural features of the vesicular-arbuscular mycorrhiza in the grapevine

A morphological analysis using transmission and scanning electron microscopy was carried out about the mycorrhizal roots of grapevine, grown in the field. Only the most common features of the endophyte, i.e. intercellular hyphae and arbuscules, were studied. The intercellular hyphae spreading the infection showed a protoplasm endowed with nuclei, mitochondria, vacuoles with dense globules and bacteria-like microorganisms. After the penetration inside the host cell, many fungal branches were found. The so formed arbuscule filled up the whole cortical cell. The different stages of the arbuscular deterioration were observed and described. The infected host cell showed beyond the usual organelles plastids with starch in close contact with the endophyte. Quelques caractéristiques ultrastructurelles des mycorrhizes du type vésiculairearbusculaire de la vigne On a étudié au moyen de microscopes electroniques à transmission et à balayage la morphologie de racines mycorrhizées prélevées dans les vignobles. L'attention a été concentrée sur les formes les plus répandues de l'endophyte, c'est-à-dire les hyphes intercellulaires et les arbuscules. Les hyphes intercellulaires, qui transmettent l'infection, ont un protoplasme muni de noyaux, de mitochondries, de vacuoles avec des globules sombres aux électrons et des micro-organismes semblables à des bactéries. A la suite de la pénétration dans la cellule de la plante-hôte, l'hyphe forme plusieures branches. L'arbuscule ainsi formé remplit complètement la cellule corticale. On a pu observer et décrire les différentes phases de dégradation de l'arbuscule. Les cellules de l'hôte infectées montrent outre les organelles normales des plastides avec de l'amidon en contact étmit avec l'endophyte

Building a mycorrhizal cell: How to reach compatibility between plants and arbuscular mycorrhizal fungi

Abstract Arbuscular mycorrhizal fungi occur throughout the majority of ecosystems supporting host plant nutrition. Recent findings describe the accommodation of the fungus by the root cell as a crucial step for compatibility between the partners. We discuss here the novel aspects of cellular plant-fungus interactions, with a particular attention to the interface compartment, the unique apoplastic space hosting intracellular fungal structures. The main features of arbuscular mycorrhizal colonization are examined and recent information in the field of plant and fungal cell responses during the establishment of the symbiosis is discussed. Differences between the colonization of root epidermal and cortical tissues are discussed, highlighting the growing interest in the role of epidermal cells during the first and decisive steps of the symbiosis. New approaches such as root organ cultures, in vivo observations, GFP tagging and mutant plant analysis are commented on and information from these is compared with t..

Cell wall remodeling in mycorrhizal symbiosis: a way towards biotrophism

Cell walls are deeply involved in the molecular talk between partners during plant and microbe interactions, and their role in mycorrhizae, i.e., the widespread symbiotic associations established between plant roots and soil fungi, has been investigated extensively. All mycorrhizal interactions achieve full symbiotic functionality through the development of an extensive contact surface between the plant and fungal cells, where signals and nutrients are exchanged. The exchange of molecules between the fungal and the plant cytoplasm takes place both through their plasma membranes and their cell walls; a functional compartment, known as the symbiotic interface, is thus defined. Among all the symbiotic interfaces, the complex intracellular interface of arbuscular mycorrhizal (AM) symbiosis has received a great deal of attention since its first description. Here, in fact, the host plasmamembrane invaginates and proliferates around all the developing intracellular fungal structures, and cell wall material is laid down between this membrane and the fungal cell surface. By contrast, in ectomycorrhizae (ECM), where the fungus grows outside and between the root cells, plant and fungal cell walls are always in direct contact and form the interface between the two partners. The organization and composition of cell walls within the interface compartment is a topic that has attracted widespread attention, both in ecto- and endomycorrhizae. The aim of this review is to provide a general overview of the current knowledge on this topic by integrating morphological observations, which have illustrated cell wall features during mycorrhizal interactions, with the current data produced by genomic and transcriptomic approaches