OmGOGAT-disruption in the ericoid mycorrhizal fungus Oidiodendron maius induces reorganization of the N pathway and reduces tolerance to heavy-metals.

Mycorrhizal fungi are key mediators of soil-to-plant movement of mineral nutrients, including essential and non-essential metals. In soil conditions that facilitate mobilization of metal ions, potentially toxic metals can interfere with nitrogen metabolism in both plants and microorganisms. Less is known about possible relationships between nitrogen metabolism and responses to heavy metals. Aim of this study was to investigate this aspect in the ericoid mycorrhizal fungus Oidiodendron maius strain Zn, a metal tolerant ascomycete. Growth of O. maius Zn on zinc and cadmium containing media was significantly affected by the nitrogen source. Screening of a library of O. maius Zn random genetic transformants for sensitivity to heavy metals (zinc and cadmium) and oxidative stress (menadione) yielded a mutant strain that carried a partial deletion of the glutamate synthase (NADH-GOGAT EC 1.4.1.14) gene and its adjacent gene, the APC15 subunit of the anaphase promoting complex. Comparison of WT and OmGOGAT-OmAPC15 mutant strains indicated an impaired N-metabolism and altered stress tolerance, and assays on the OmAPC15-recomplemented strains ascribed the observed phenotypes to the deletion in the OmGOGAT gene. OmGOGAT disruption modified the nitrogen pathway, with a strong reduction of the associated glutamine synthetase (GS, EC 6.3.1.2) activity and an up-regulation of the alternative NADP-glutamate dehydrogenase (NADP-GDH, EC 1.4.1.4) pathway for glutamate biosynthesis. Unless they were supplemented with glutamine, O. maius Zn transformants lacking OmGOGAT were very sensitive to zinc. These results highlight the importance of nitrogen metabolism not only for nitrogen assimilation and transformation, but also for stress tolerance. For mycorrhizal fungi, such as O. maius, this may bear consequences not only to the fungus, but also to the host plant.

Proteome changes in Oncidium sphacelatum (Orchidaceae) at different trophic stages of symbiotic germination.

Mutualistic symbioses between plants and fungi are a widespread phenomenon in nature. Particularly in orchids, association with symbiotic fungi is required for seed germination and seedling development. During the initial stages of symbiotic germination, before the onset of photosynthesis, orchid protocorms are fully mycoheterotrophic. The molecular mechanisms involved in orchid symbiotic germination and development are largely unknown, but it is likely that changes in plant energy metabolism and defense-related responses play a central role in these processes. We have used 2D-LC-MS/MS coupled to isobaric tagging for relative and absolute quantification to identify proteins with differential accumulation in Oncidium sphacelatum at different stages of mycorrhizal protocorm development (achlorophyllous and green protocorms) after seed inoculation with a Ceratobasidium sp. isolate. We identified and quantified 88 proteins, including proteins putatively involved in energy metabolism, cell rescue and defense, molecular signaling, and secondary metabolism. Quantitative analysis showed that the expected changes in carbon metabolism in green protocorms were accompanied by enhanced accumulation of proteins involved in the modulation of reactive oxygen species homeostasis, defense-related responses, and phytoalexins and carotenoid biosynthesis. Our results suggest profound metabolic changes in orchid protocorms during the switch from the fully mycoheterotrophic to the photosynthetic stage. Part of these changes may be also related to the obligatory nature of the interaction with the endomycorrhizal fungus.

A PLAC8-containing protein from an endomycorrhizal fungus confers cadmium resistance to yeast cells by interacting with Mlh3p.

Cadmium is a genotoxic pollutant known to target proteins that are involved in DNA repair and in antioxidant defence, altering their functions and ultimately causing mutagenic and carcinogenic effects. We have identified a PLAC8 domain-containing protein, named OmFCR, by a yeast functional screen aimed at identifying genes involved in cadmium resistance in the endomycorrhizal fungus Oidiodendron maius. OmFCR shows a remarkable specificity in mediating cadmium resistance. Both its function and its nuclear localization in yeast strictly depend on the interaction with Mlh3p, a subunit of the mismatch repair (MMR) system. Although proteins belonging to the PLAC8 family are widespread in eukaryotes, they are poorly characterized and their biological role still remains elusive. Our work represents the first report about the potential role of a PLAC8 protein in physically coupling DNA lesion recognition by the MMR system to appropriate effectors that affect cell cycle checkpoint pathways. On the basis of cell survival assays and yeast growth curves, we hypothesize that, upon cadmium exposure, OmFCR might promote a higher rate of cell division as compared to control cells.

A search for predictive factors for hypersensitivity reactions to paclitaxel and platinum salts in chemotherapy for gynecologic pelvic neoplasms.

AIMS: To investigate the frequency of and predictive factors for hypersensitivity reactions (HR) to taxanes and platinum salts in a cohort of patients treated for pelvic gynecologic malignancies. METHODS: The medical records of all patients with gynecologic pelvic neoplasms treated with chemotherapy at the Department of Gynecologic Oncology, AO Mauriziano Umberto I of Turin, from September 2007 through August 2008, were retrospectively reviewed. Two multivariate models, regarding carboplatin and taxane chemotherapy, respectively, were performed to evaluate the potential predictive value of various clinical features. RESULTS: The incidence of HR was 14% (22/157). Multivariate models showed that menopausal women had a significantly lower probability of HR (OR 0.12, CI 0.02-1.13, p = 0.06 for the carboplatin model and OR 0.05, CI 0.01-0.63, p = 0.02 for the taxane model) while a history of systemic hypersensitivity was associated with a higher but non-significant risk of HR (OR 2.64, CI 0.78-8.95, p = 0.11, for the carboplatin model and OR 3.42, CI 0.94-12.45, p = 0.06, for the taxane model). CONCLUSION: We confirmed a history of hypersensitivity as a risk factor for HR. Other larger cohorts should be analyzed: we need to find new predictive factors in order to select women who should be submitted to experimental prophylactic strategies.

Light-induced charge generation in polymeric nanoparticles restores vision in advanced-stage retinitis pigmentosa rats.

Retinal dystrophies such as Retinitis pigmentosa are among the most prevalent causes of inherited legal blindness, for which treatments are in demand. Retinal prostheses have been developed to stimulate the inner retinal network that, initially spared by degeneration, deteriorates in the late stages of the disease. We recently reported that conjugated polymer nanoparticles persistently rescue visual activities after a single subretinal injection in the Royal College of Surgeons rat model of Retinitis pigmentosa. Here we demonstrate that conjugated polymer nanoparticles can reinstate physiological signals at the cortical level and visually driven activities when microinjected in 10-months-old Royal College of Surgeons rats bearing fully light-insensitive retinas. The extent of visual restoration positively correlates with the nanoparticle density and hybrid contacts with second-order retinal neurons. The results establish the functional role of organic photovoltaic nanoparticles in restoring visual activities in fully degenerate retinas with intense inner retina rewiring, a stage of the disease in which patients are subjected to prosthetic interventions.

Merkel cells and permanent disesthesia in the oral mucosa after soft tissue grafts.

Connective tissue grafts are routinely procedures in the treatment of gingival defects. The clinical success of the gingival tissue graft procedures anyway should ensure not only the aesthetic integration between the tissues but also the physiological activity of the graft in terms of sensitivity and immunity because the skin and the mucosae constitute the first natural aspecific borders against pathogens. The aim of this paper was to investigate nervous net recovery after connective graft procedure, in relation with sensorial alteration in the injured area. Results showed that there is a close link among the number of Merkel cells and the alteration of sensations. Merkel cells can be found isolated standing in the basal layer, supposed to have neuroendocrine functions in the epithelia or in larger group not associated with nerves; when found in association with nerves they are named Merkel complexes, acting as slow adapter mechanical receptor. Our data can be explained in two ways: Merkel cells increase as a consequence of tissue injury, a sort of "SOS cells" that secrete neuroendocrine signals to guide tissue healing; as an alternative the presence of the Merkel cells could be read as a derailment of tissue regeneration with the stop of cellular differentiation in the direction of an abnormal proliferation, a sort of mad stem cell.

SOD1-targeted gene disruption in the ericoid mycorrhizal fungus Oidiodendron maius reduces conidiation and the capacity for mycorrhization.

The genome sequences of mycorrhizal fungi will provide new opportunities for studying the biology and the evolution underlying this symbiotic lifestyle. The generation of null mutants at the wild-type loci is one of the best methods for gene-function assignment in the post-genomic era. To our knowledge, the generation of superoxide dismutase 1 (SOD1)-null mutants in the ericoid mycorrhizal fungus Oidiodendron maius is the first example of a gene-targeted disruption via homologous recombination in a mycorrhizal fungus. The disruption of OmSOD1 by Agrobacterium-mediated transformation resulted in the presence of oxidative stress markers, even in the absence of external superimposed stresses, and an increased sensitivity to reactive oxygen species (ROS)-generating substances, especially to menadione. A reduction in conidiation and in the percentage of mycorrhization of Vaccinium myrtillus roots was also observed. The latter findings establish the pivotal role of SOD1 as an important factor in the relationship between O. maius and its symbiotic partner. The lack of this ROS-scavenger may cause an imbalance in the redox homeostasis during host colonization and an alteration in the delicate dialogue between the fungus and its host plant.

Is aortic lymphadenectomy indicated in locally advanced cervical cancer after neoadjuvant chemotherapy followed by radical surgery? A retrospective study on 261 women.

OBJECTIVES: The aim of this study was to estimate the rate of aortic lymph nodes (LN) metastases/recurrences among patients affected by locally advanced stage cancer patients (LACC), treated with neoadjuvant chemotherapy (NACT) and radical surgery. METHODS: Retrospective evaluation of consecutive 261 patients affected by LACC (stage IB2-IIB), treated with NACT followed by radical surgery at National Cancer Institute, Milan, Italy, between 1990 and 2011. RESULTS: Stage at presentation included stage IB2, IIA and IIB in 100 (38.3%), 50 (19.2%) and 111 (42.5%) patients, respectively. Squamous cell carcinoma accounted for more than 80%, followed by adenocarcinoma or adenosquamous cancers (20%). Overall, 56 women (21.5%) had LN metastases. Four out of 83 women (5%) who underwent both pelvic and aortic LN dissection had aortic LN metastases, and all women had concomitant pelvic and aortic LN metastases. Only one woman out of 178 (0.5%) who underwent pelvic lymphadenectomy only, had an aortic LN recurrence. Overall 2% of women (5/261) had aortic LN metastases/recurrence. CONCLUSIONS: Our data suggest that aortic lymphadenectomy at the time of surgery is not routinely indicated in LACC after NACT, but should reserved in case of bulky LN in both pelvic and/or aortic area. The risk of isolated aortic LN relapse is negligible. Further prospective studies are warranted.

Bacterial associations with mycorrhizal fungi: close and distant friends in the rhizosphere.

Bacteria and mycorrhizal fungi in the rhizosphere interact with each other at different levels of cellular integration, ranging from apparently simple association, through surface attachment, to intimate and obligatory symbiosis. This synergism may not only be important in promoting plant growth and health, but may also be significant to rhizosphere ecology.

Common and metal-specific proteomic responses to cadmium and zinc in the metal tolerant ericoid mycorrhizal fungus Oidiodendron maius Zn.

Although adaptive metal tolerance may arise in fungal populations in polluted soils, the mechanisms underlying metal-specific tolerance are poorly understood. Comparative proteomics is a powerful tool to identify variation in protein profiles caused by changing environmental conditions, and was used to investigate protein accumulation in a metal tolerant isolate of the ericoid mycorrhizal fungus Oidiodendron maius exposed to zinc and cadmium. Two-dimensional gel electrophoresis and shotgun proteomics followed by mass spectrometry lead to the identification of common and metal-specific proteins and pathways. Proteins selectively induced by cadmium exposure were molecular chaperons of the Hsp90 family, cytoskeletal proteins and components of the translation machinery. Zinc significantly up-regulated metabolic pathways related to energy production and carbohydrates metabolism, likely mirroring zinc adaptation of this fungal isolate. Common proteins induced by the two metal ions were the antioxidant enzyme Cu/Zn superoxide dismutase and ubiquitin. In mycelia exposed to zinc and cadmium, both proteomic techniques also identified agmatinase, an enzyme involved in polyamine biosynthesis. This novel finding suggests that, like plants, polyamines may have important functions in response to abiotic environmental stress in fungi. Genetic evidence also suggests that the biosynthesis of polyamines via an alternative metabolic pathway may be widespread in fungi.

Mucoid mutants of the biocontrol strain pseudomonas fluorescens CHA0 show increased ability in biofilm formation on mycorrhizal and nonmycorrhizal carrot roots.

Extracellular polysaccharides play an important role in the formation of bacterial biofilms. We tested the biofilm-forming ability of two mutant strains with increased production of acidic extracellular polysaccharides compared with the wild-type biocontrol strain Pseudomonas fluorescens CHA0. The anchoring of bacteria to axenic nonmycorrhizal and mycorrhizal roots as well as on extraradical mycelium of the arbuscular mycorrhizal fungus Glomus intraradices was investigated. The nonmucoid wild-type strain P. fluorescens CHA0 adhered very little on all surfaces, whereas both mucoid strains formed a dense and patchy bacterial layer on the roots and fungal structures. Increased adhesive properties of plant-growth-promoting bacteria may lead to more stable interactions in mixed inocula and the rhizosphere.

Bacterial and plant glycoconjugates at the Rhizobium-legume interface.

Many classes of bacterial and plant glycoconjugate have been shown to be involved in establishing the Rhizobium root nodule symbiosis with peas (Pisum sativum). It was demonstrated, using techniques of molecular genetics, that a group of Rhizobium nodulation genes (nod genes) co-operate to synthesize a lipo-oligosaccharide signal molecule that specifically initiates nodule development on legume hosts. An additional gene function, encoded by nodX, has been found to extend the host range of Rhizobium leguminosarum bv. viciae to include nodulation of a pea mutant, cultivar Afghanistan; the nodX gene product specifies the addition of an acetyl group to the terminal N-acetylglucosamine residue at the reducing end of the pentasaccharide core of this signal molecule. Several other classes of bacterial glycoconjugate have also been shown by genetic analysis to be essential for normal nodule development and function: these include a capsular extracellular polysaccharide; lipopolysaccharide in the outer membrane; and cyclic glucans present in the periplasmic space. Potential functions for these glycoconjugates are discussed in the context of tissue and cell invasion by Rhizobium. Some plant components involved in symbiotic interactions have been identified by the analysis of nodule-specific gene expression (early nodulins). Several of the cDNA clones encoding these early nodulins specify proline-rich proteins that presumably correspond to cell wall glycoproteins or membrane arabinogalactan proteins. Other plant glycoconjugates have been identified using monoclonal antibodies as probes. A plant glycoprotein present in intercellular spaces has been identified as a component of the luminal matrix of infection threads. Because it attaches to the surface of bacteria and is itself susceptible to oxidative cross-linking, this glycoprotein may be involved in limiting the progress of microbial infections. Endocytosis of bacteria into the plant cytoplasm is apparently driven by direct interactions between the bacterial surface and the plasma membrane that is exposed within an unwalled infection droplet; glycoprotein and glycolipid components of the plant membrane glycocalyx have been defined using monoclonal antibodies. Differentiation of endosymbiotic bacteroids is preceded by differentiation of the plant-derived peribacteroid membrane which encloses the symbiosome compartment. Using a monoclonal antibody that identifies a group of plant membrane-associated, inositol-containing glycolipids, we have identified a very early marker for the differentiation of peribacteroid membrane from plasma membrane.

Zinc ions alter morphology and chitin deposition in an ericoid fungus.

A sterile mycelium PS IV, an ascomycete capable of establishing ericoid mycorrhizas, was used to investigate how zinc ions affect the cellular mechanisms of fungal growth. A significant reduction of the fungal biomass was observed in the presence of millimolar zinc concentrations; this mirrored conspicuous changes in hyphal morphology which led to apical swellings and increased branching in the subapical parts. Specific probes for fluorescence and electron microscopy localised chitin, the main cell wall polysaccharide, on the inner part of the fungal wall and on septa in control specimens. In Zn-treated mycelium, hyphal walls were thicker and a more intense chitin labelling was detected on the transverse walls. A quantitative assay showed a significant increase in the amount of chitin in metal-treated hyphae.

Extracellular polysaccharides are involved in the attachment of Azospirillum brasilense and Rhizobium leguminosarum to arbuscular mycorrhizal structures.

Arbuscular mycorrhizal (AM) fungi, one of the most important component of the soil microbial community, establish physical interactions with naturally occurring and genetically modified bacterial biofertilizers and biopesticides, commonly referred to as plant growth-promoting rhizobacteria (PGPR). We have used a genetic approach to investigate the bacterial components possibly involved in the attachment of two PGPR (Azospirillum and Rhizobium) to AM roots and AM fungal structures. Mutants affected in extracellular polysaccharides (EPS) have been tested in in vitro adhesion assays and shown to be strongly impaired in the attachment to both types of surfaces as well as to quartz fibers. Anchoring of rhizobacteria to AM fungal structures may have special ecological and biotechnological significance because it may facilitate colonisation of new rhizospheres by the bacteria, and may be an essential trait for the development of mixed inocula.

Could follow-up different modalities play a role in asymptomatic cervical cancer relapses diagnosis? An Italian multicenter retrospective analysis.

OBJECTIVE: The aim of this study was to evaluate how much clinical surveillance performed by follow-up scheduled appointments may correctly identify asymptomatic recurrences and describe the pattern of relapse detected by procedures. METHODS: The records of 327 consecutive women with recurrent cervical cancer treated from 1980 to 2005 were retrospectively collected in 8 Italian Institutions. Primary disease and recurrence data were picked up: diagnosis, type of treatment, FIGO stage, tumour grade, histology, clinical lesion size, number of localizations and site of relapse, presence of symptoms and primary method of detection, the type of treatment of recurrence and follow-up data, such as appointment date, clinical status and procedure performed. A multivariate analysis was carried out using the Cox proportional hazards regression model. Survival curves were calculated using the Kaplan-Meier technique. Survival differences were evaluated by the log-rank test. RESULTS: Sixty-seven out of 327 patients (20.5%) had a local recurrence on vaginal vault, 120 (36.7%) in central pelvis, 31 (9.5%) in pelvic wall, 16 cases (4.9%) in lymph nodes. Seventy-nine patients (24.2%) showed a distant relapse while 14 (4.3%) developed both a distant and local relapse. Among patients with distant relapses 39 (49.4%) had lung metastasis, 41 (51.9%) an hepatic recurrence, 4 (5.1%) a bone relapse. Among distant sites 32 out of 79 patients (40.5%) had single relapse and 46 (58.2%) had multiple localizations. The site of relapse influenced survival since patients with vaginal vault recurrences lived significantly longer than patients with recurrences in other sites. Ninety-seven (29.7%) patients were symptomatic and anticipated the scheduled visit, 66 (20.2%) reported their symptoms during the follow-up visit and 164 (50.1%) were asymptomatic and the diagnostic path was introduced by a planned visit or exam. Between asymptomatic patients the first procedure was clinical visit for 85 patients out of 164 patients (51.8%), imaging for 60 patients (36.6%), both clinical visit and imaging for 14 (8.5%) and cytology for 5 (3%, Pap smear test). The median OS of symptomatic patients was 37 months versus 109 months of asymptomatic patients (Log rank, p=0.00001). The median survival since recurrence was 9 months for symptomatic patients and median was not reached for asymptomatic patients (p<0.0001). The median disease-free interval was 24 months for asymptomatic patients vs. 36 months for symptomatic patients (p=0.03). CONCLUSIONS: Our study helps demonstrate the great need of prospective cost-effectiveness studies which are lacking at the present time.

Inefficient photosynthesis in the Mediterranean orchid Limodorum abortivum is mirrored by specific association to ectomycorrhizal Russulaceae.

Among European Neottieae, Limodorum abortivum is a common Mediterranean orchid. It forms small populations with a patchy distribution in woodlands, and is characterized by much reduced leaves, suggesting a partial mycoheterotrophy. We have investigated both the photosynthetic abilities of L. abortivum adult plants and the diversity of mycorrhizal fungi in Limodorum plants growing in different environments and plant communities (coniferous and broadleaf forests) over a wide geographical and altitudinal range. Despite the presence of photosynthetic pigments, CO2 fixation was found to be insufficient to compensate for respiration in adult plants. Fungal diversity was assessed by morphological and molecular methods in L. abortivum as well as in the related rare species Limodorum trabutianum and Limodorum brulloi. Phylogenetic analyses of the fungal internal transcribed spacer (ITS) sequences, obtained from root samples of about 80 plants, revealed a tendency to associate predominantly with fungal symbionts of the genus Russula. Based on sequence similarities with known species, most root endophytes could be ascribed to the species complex encompassing Russula delica, Russula chloroides, and Russula brevipes. Few sequences clustered in separate groups nested within Russula, a genus of ectomycorrhizal fungi. The morphotypes of ectomycorrhizal root tips of surrounding trees yielded sequences similar or identical to those obtained from L. abortivum. These results demonstrate that Limodorum species with inefficient photosynthesis specifically associate with ectomycorrhizal fungi, and appear to have adopted a nutrition strategy similar to that known from achlorophyllous orchids.

Ericoid mycorrhizal fungi are common root associates of a Mediterranean ectomycorrhizal plant (Quercus ilex).

Mycorrhiza samples of neighbouring Quercus ilex and Erica arborea plants collected in a postcutting habitat were processed to see whether plants differing in mycorrhizal status harbour the same root endophytes. Three experiments were performed in parallel: (i) isolation, identification and molecular characterization of fungi from surface-sterilized roots of both plant species; (ii) re-inoculation of fungal isolates on axenic E. arborea and Q. ilex seedlings; (iii) direct inoculation of field-collected Q. ilex ectomycorrhizas onto E. arborea seedlings. About 70 and 150 fungal isolates were obtained from roots of Q. ilex and E. arborea, respectively. Among them, Oidiodendron species and five cultural morphotypes of sterile isolates formed typical ericoid mycorrhizas on E. arborea in vitro. Fungi with such mycorrhizal ability were derived from both host plants. Isolates belonging to one of these morphotypes (sd9) also exhibited an unusual pattern of colonization, with an additional extracellular hyphal net. Ericoid mycorrhizas were also readily obtained by direct inoculation of E. arborea seedlings with Q. ilex ectomycorrhizal tips. Polymerase chain-restriction fragment length polymorphism and random amplified polymorphic DNA analyses of the shared sterile morphotypes demonstrate, in the case of sd9, the occurrence of the same genet on the two host plants. These results indicate that ericoid mycorrhizal fungi associate with ectomycorrhizal roots, and the ecological significance of this finding is discussed.

Detection and identification of bacterial endosymbionts in arbuscular mycorrhizal fungi belonging to the family Gigasporaceae.

Intracellular bacteria have been found previously in one isolate of the arbuscular mycorrhizal (AM) fungus Gigaspora margarita BEG 34. In this study, we extended our investigation to 11 fungal isolates obtained from different geographic areas and belonging to six different species of the family Gigasporaceae. With the exception of Gigaspora rosea, isolates of all of the AM species harbored bacteria, and their DNA could be PCR amplified with universal bacterial primers. Primers specific for the endosymbiotic bacteria of BEG 34 could also amplify spore DNA from four species. These specific primers were successfully used as probes for in situ hybridization of endobacteria in G. margarita spores. Neighbor-joining analysis of the 16S ribosomal DNA sequences obtained from isolates of Scutellospora persica, Scutellospora castanea, and G. margarita revealed a single, strongly supported branch nested in the genus Burkholderia.

Cellulose and pectin localization in roots of mycorrhizalAllium porrum: labelling continuity between host cell wall and interfacial material.

Two different types of contacts (or interfaces) exist between the plant host and the fungus during the vesicular-arbuscular mycorrhizal symbiosis, depending on whether the fungus is intercellular or intracellular. In the first case, the walls of the partners are in contact, while in the second case the fungal wall is separated from the host cytoplasm by the invaginated host plasmamembrane and by an interfacial material. In order to verify the origin of the interfacial material, affinity techniques which allow identification in situ of cell-wall components, were used. Cellobiohydrolase (CBH I) that binds to cellulose and a monoclonal antibody (JIM 5) that reacts with pectic components were tested on roots ofAllium porrum L. (leek) colonized byGlomus versiforme (Karst.) Berch. Both probes gave a labelling specific for the host cell wall, but each probe labelled over specific and distinct areas. The CBH I-colloidal gold complex heavily labelled the thick epidermal cell walls, whereas JIM 5 only labelled this area weakly. Labelling of the hypodermis was mostly on intercellular material after treatment with JIM 5 and only on the wall when CBH I was used. Suberin bands found on the radial walls were never labelled. Cortical cells were mostly labelled on the middle lamella with JIM 5 and on the wall with CBH I. Gold granules from the two probes were found in interfacial material both near the point where the fungus enters the cell and around the thin hyphae penetrating deep into the cell. The ultrastructural observations demonstrate that cellulose and pectic components have different but complementary distributions in the walls of root cells involved in the mycorrhizal symbiosis. These components show a similar distribution in the interfacial material laid down around the vesicular-arbuscular mycorrhizal fungus indicating that the interfacial material is of host origin.