A mycorrhizal fungus changes microtubule orientation in tobacco root cells

Summary Cortical cells of mycorrhizal roots undergo drastic morphological changes, such as vacuole fragmentation, nucleus migration, and deposition of cell wall components at the plant-fungus interface. We hypothesized that the cytoskeleton is involved in these mechanisms leading to cell reorganization. We subjected longitudinal, meristem to basal zone, sections of uninfectedNicotiana tabacum roots to immunofluorescence methods to identify the microtubular (MT) structures associated with root cells. Similar sections were obtained from tobacco roots grown in the presence ofGigaspora margarita, an arbuscular mycorrhizal fungus which penetrates the root via the epidermal cells, but mostly develops in the inner cortical cells. While the usual MT structures were found in uninfected roots (e.g., MTs involved in mitosis in the meristem and cortical hoops in differentiated parenchyma cells), an increase in complexity of MT structures was observed in infected tissues. At least three new systems were identified: (i) MTs running along large intracellular hyphae, (ii) MTs linking hyphae, (iii) MTs binding the hyphae to the host nucleus. The experiments show that mycorrhizal infection causes reorganization of root MTs, suggesting their involvement in the drastic morphological changes shown by the cortical cells.     

Chitinase in roots of mycorrhizal Allium porrum: regulation and localization

Chitinase (EC 3.2.1.14) activity was measured in roots of Allium prorrum L. (leek) during development of a vesicular-arbuscular mycorrhizal symbiosis with Glomus versiforme (Karst.) Berch. During the early stages of infection, between 10 and 20 d after inoculation, the specific activity of chitinase was higher in mycorrhizal roots than in the uninfected controls. However, 60–90 d after inoculation, when the symbiosis was fully established, the mycorrhizal roots contained much less chitinase than control roots. Chitinase was purified from A. porrum roots. An antiserum against beanleaf chitinase was found to cross-react specifically with chitinase in the extracts from non-mycorrhizal and mycorrhizal A. porrum roots. This antiserum was used for the immunocytochemical localization of the enzyme with fluorescent and gold-labelled probes. Chitinase was localized in the vacuoles and in the extracellular spaces of non-mycorrhizal and mycorrhizal roots. There was no immunolabelling on the fungal cell walls in the intercellular or the intracellular phases. It is concluded that the chitin in the fungal walls is inaccessible to plant chitinase. This casts doubts on the possible involvement of this hydrolase in the development of the mycorrhizal fungus. However, fungal penetration does appear to cause a typical defense response in the first stages that is later depressed.     

Effect of fungal-isolate aggressivity on the biosynthesis of symbiosis-related polypeptides in differentiating eucalypt ectomycorrhizas

Changes in protein biosynthesis were examined during the early stages of differentiation of Eucalyptus grandis-Pisolithus tinctorius ectomycorrhizas by two-dimensional polyacrylamide gel electrophoresis of ³⁵S-labelled proteins. Three distinct isolates of P. tinctorius Coker & Couch were chosen based on the rate of ectomycorrhizal formation (i.e. infectivity) with E. grandis W. Hill ex Maiden. The isolate H506 was not able to induce mycorrhiza, isolate 441 showed moderate infectivity and isolate H2144 exhibited a very high infectivity. Mycorrhiza were produced in vitro in a system where seeds were germinated in the presence of fungal mycelium and exudates. The non-mycorrhizal isolate caused no changes in root protein biosynthesis as analyzed by two-dimensional polyacrylamide gel electrophoresis, whereas drastic alterations in protein biosynthesis were observed from initial contact with the aggressive mycobionts. During mycorrhizal development, there was a marked inhibition of plant polypeptides synthesis, enhanced accumulation of some fungal polypeptides and the emergence of symbiosis-specific polypeptides, the so-called ectomycorrhizins. The major changes were observed in a group of fungal acidic polypeptides (apparent molecular weight 28–32 kDa) including the ectomycorrhizin E₃₂. These polypeptides first appeared at contact and their synthesis increased during mycorrhizal formation, suggesting a role in mycorrhizal development, most likely as structural proteins. Up-regulation of the synthesis of fungal symbiosis-related polypeptides was tightly correlated to the infectivity of the strain.Abbreviations FW fresh weight - MW molecular weight - pI isoelectric point - SR-polypeptides symbiosis-related polypeptides This work was supported by a research grant from the Eureka-Eurosilva programme (Changes in Gene Expression during Ectomycorrhiza Differentiation and Function) to F.M. and a Murdoch University Special Research Grant to B.D; T.B. was a recipient of a Doctoral Fellowship from the INRA and an Australian Postgraduate Scholarship. We would like to thank Dr Denis Tagu and Dulcinéia de Carvalho (Institut National de la Recherche Agronomique, Nancy, France) for helpful discussions.     

Mycorrhizal differences between genuine roots and tuberous roots of adult plants ofSpiranthes sinensis var.amoena (Orchidaceae)

Genuine roots ofSpiranthes sinensis var.amoena were infected with the mycorrhizal fungusRhizoctonia repens immediately after root formation in autumn. Infection by the mycorrhizal fungus extended, reaching a maximum the following early summer. The amount of living mycorrhizal fungus in the genuine roots dramatically declined in the flowering season, and then the roots decomposed. Tuberous roots were formed in spring. Mycorrhizas were limited to local infections and did not spread along the roots. The infection level of living mycorrhizal fungus in the tuberous roots was less than in the genuine roots throughout the year. The amount of dead fungal coils in the tuberous roots increased as the tuberous roots aged. The mycorrhizal characteritics of tuberous roots ofS. sinensis var.amoena were totally different from those of genuine roots although the tuberous roots morphologically resembled the genuine roots. Contribution No. 96, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Polyploidy in tomato roots as affected by arbuscular mycorrhizal colonization

Nuclear changes in roots of tomato (Lycopersicon esculentum), a plant with a small genome, during the establishment of arbuscular mycorrhizal (AM) colonization were studied using light and electron microscopy, as well as flow and static cytometry. Nuclei of mycorrhizal root cortex cells were larger and had more decondensed chromatin than those of controls. Significant ploidy distribution differences were observed between nuclei of AM colonized and control roots, and a strong correlation between nuclear polyploidization and AM colonization was found. Polyploidization and decondensation are usually associated with high metabolic activity. The metabolic activity of mycorrhizal root cells, evaluated in this work as respiratory activity by using a cytochemical assay for succinate dehydrogenase combined with image analysis, increased in comparison to controls. The meaning of polyploidization is discussed in relation to the structural and metabolic modifications induced by mycorrhization.     

Colonisation patterns of root tissues byPhytophthora nicotianae var.parasitica related to reduced disease in mycorrhizal tomato

Tomato plants pre-colonised by the arbuscular mycorrhizal fungusGlomus mosseae showed decreased root damage by the pathogenPhytophthora nicotianae var.parasitica. In analyses of the cellular bases of their bioprotective effect, a prerequisite for cytological investigations of tissue interactions betweenG. mosseae andP. nicotianae v.parasitica was to discriminate between the hyphae of the two fungi within root tissues. We report the use of antibodies as useful tools, in the absence of an appropriate stain for distinguishing hyphae ofP. nicotianae v.parasitica from those ofG. mosseae inside roots, and present observations on the colonisation patterns by the pathogenic fungus alone or during interactions in mycorrhizal roots. Infection intensity of the pathogen, estimated using an immunoenzyme labelling technique on whole root fragments, was lower in mycorrhizal roots. Immunogold labelling ofP. nicotianae v.parasitica on cross-sections of infected tomato roots showed that inter or intracellular hyphae developed mainly in the cortex, and their presence induced necrosis of host cells, the wall and contents of which showed a strong autofluorescence in reaction to the pathogen. In dual fungal infections of tomato root systems, hyphae of the symbiont and the pathogen were in most cases in different root regions, but they could also be observed in the same root tissues. The number ofP. nicotianae v.parasitica hyphae growing in the root cortex was greatly reduced in mycorrhizal root systems, and in mycorrhizal tissues infected by the pathogen, arbuscule-containing cells surrounded by intercellularP. nicotianae v.parasitica hyphae did not necrose and only a weak autofluorescence was associated with the host cells. Results are discussed in relation to possible processes involved in the phenomenon of bioprotection in arbuscular mycorrhizal plants.     

Defence-related Enzymes in Pepper Roots During Interactions with Arbuscular Mycorrhizal Fungi and/or Verticillium dahliae

Previous studies have described that arbuscular mycorrhizal fungi (AMF) can reduce the deleterious effect of Verticillium dahliae Kleb. on pepper growth and yield. In mycorrhizal plants, the bioprotection against soil-borne pathogens can result from the preactivation of defence responses that include some structural modifications and the accumulation of Pathogenesis-Related (PR) proteins. Our first objective was to study if V. dahliae induced defence mechanisms in roots before infected pepper developed visible symptoms of disease. The second aim was to determine if AMF induced defence-related enzymatic activities in pepper roots before or after pathogen’s attack. Results showed that the colonization of pepper roots by Glomus deserticola (Trappe, Bloss and Menge) induced the appearance of new isoforms of acidic chitinases, superoxide dismutase (SOD) and, at early stages, peroxidases. In contrast, V. dahliae neither stimulated the phenylpropanoid pathway nor elicited hydrolytic activities in infected pepper roots. Only in mycorrhizal plants, the inoculation with V. dahliae slightly increased both phenylalanine ammonia-lyase (PAL) and peroxidase activities two weeks later. Mycorrhizal-specific induction of new isoforms of acidic chitinases and SOD together with enhanced peroxidase and PAL activities 2 weeks after pathogen inoculation could be involved in the biocontrol of Verticillium-induced wilt in pepper by AMF.     

Root colonization of different hosts by the vesicular-arbuscular mycorrhizal fungus Glomus dimorphicum

Colonization of the roots of beans, alfalfa, onions, red clover, corn, and four barley cultivars (Bonanza, Klondike, Gateway 63, and Olli) by Glomus dimorphicum Boyetchko and Tewari, a vesicular-arbuscular mycorrhizal fungus isolated from a barley field in Alberta, Canada, was studied under greenhouse conditions. Infection levels were low in all four barley cultivars but were higher in beans, alfalfa, and onions and were highest in red clover and corn roots. The infection patterns of G. dimorphicum varied among all the hosts. Coiling of intracellular hyphae occurred in corn, alfalfa, and red clover roots. Appreciable numbers of intraradical vesicles were found only in red clover and bean roots, while arbuscules formed in all hosts except barley. It was concluded that the pattern of root colonization by G. dimorphicum is influenced by the host genome and that the fungal morphology in the roots is variable and, thus, not diagnostic for the mycorrhizal species.     

Occurrence and importance of mycorrhizae in aquatic trees of New South Wales,Australia

Vesicular arbuscular mycorrhizal (VAM) infection was found in KOH-cleared and lactophenolblue-stained roots of Salix babylonica, Melaleuca quinquenervia and Casuarina cunninghamiana. These are all trees growing on creeks and river banks, in stationary or slowly flowing fresh or brackish waters in swamps, creeks, drains and channels, and in seepage areas of New South Wales, Australia. Larger and older roots lacked VAM infection in the inner cortex, probably due to suberisation of cells, and the endophyte was restricted to the epidermal layers. Spores and sporocarps of the VAM fungi Glomus fasciculatus, G. mosseae, Sclerocystis rubiformis, Gigaspora margarita and an unidentified Scutellospora sp. were wet sieved and decanted from aquatic sediments and soils. The presence of similar VAM fungal spores in the aquatic sediments and terrestrial soil suggests that they probably enter the aquatic sediments through run off from the land ecosystem. All three plants formed vesicular arbuscular (VA) mycorrhizae almost exclusively in the marshy, periodically inundated soils, but the same plant species formed endo-/ ectomycorrhizae when growing in soil with higher redox potentials (E _h). Salix and Melaleuca tree roots possessed both VAmycorrhizae and ectomycorrhizae. VAM roots of Casuarina were equipped with both N-fixing Frankia nodules and proteoid roots. VAM endophytes did not invade nodular cortical tissues, suggesting the presence of an exclusion mechanism which needs further study. The highest VAM infection was found in nodulated specimens. Free-floating roots growing in water close to the banks were non-mycorrhizal but were mycorrhizal in the bottom-rooting state. VAM spore number and mycorrhizal infection seem to be associated with redox-potential, i.e. lower at sites such as swamps, water or sediments with lower E _h values than in terrestrial soils with higher E _h values. A relationship between soil moisture gradient and VAM infection pattern became apparent from the study of a C. cunninghamiana transect on a creek embankment, i.e. typical vesicles and arbuscules were found in roots from drier soils, there was a lack of arbuscules in relatively wet soils but large lipid-filled intracellular vesicles were present, and typical vesicles and arbuscules were absent in flooded creek beds where roots were associated with coenocytic intercellular hyphae with abundant lipid droplets. The importance of VA mycorrhiza, ectomycorrhizae, N-fixing root nodules and proteoid roots at the land-water interface is discussed with reference to the use of these trees as pioneering species for stabilising river and stream banks, reducing erosion, windbreaking, and as a long-term and inexpensive means of achieving biological control of aquatic weeds by shading waterways.     

Protein patterns and superoxide dismutase activity in non-mycorrhizal and arbuscular mycorrhizalPisum sativum L. plants

There are few reports in relation to the role of specific proteins in the mycorrhizal symbiosis. Among the changes in the protein expression as a consequence of the arbuscular mycorrhizal symbiosis, only one case related to changes in superoxide dismutase (SOD; EC 1.15.1.1) activity has been reported in the red clover-Glomus mosseae symbiosis.In this paper, the symbiotic system formed by a leguminous plant,Pisum sativum, and the fungusGlomus mosseae is studied in terms of protein patterns and SOD activity in both mycorrhizal and non-mycorrhizal roots. Our results show that among the differential polypeptides separated by SDS-PAGE, one with a molecular weight of 32.0 kDa, and a protein with an isoelectric point of pI 4.9 appeared strongly expressed in mycorrhizal roots. A partial purification of the related polypeptide could be achieved by DEAE-cellulose chromatography. A higher SOD activity was also detected in mycorrhizal pea roots, although both mycorrhizal and non-mycorrhizal roots showed the same isoenzymatic pattern for SODs: two Mn-SODs (I and II) and two Cu,Zn-SODs (I and II) were detected, Cu,Zn-SOD I being the most abundant isozyme in both types of roots. A similar pattern of SOD isozymes (Mn-SODs I and II, and Cu,Zn-SODs I and II) was also found in nodules of mycorrhizal and non-mycorrhizal pea roots. However, in nodules Mn-SOD II was the main isozyme. The bacterial nature of this isozyme is postulated in this report.Dr. Justo Arines died on the 15th November, 1993 in Dijon (France), while he was attending a molecular biology course on mycorrhizas.     

Mycorrhizal fungi and the nutrient ecology of three oldfield annual plant species

Summary Three oldfield annual species (Abutilon theophrasti Medic., Ambrosia artemisiifolia L. and Setaria lutescens (Weigel) Hubb.) were investigated. All three developed substantial mycorrhizal infections when inoculated with Glomus etunicatum Becker & Gerd. Mycorrhizal infection dramatically increased phosphorus content and dry weight of both Abutilon and Ambrosia, but did not significantly affect dry weight and only modestly increased phosphorus content of Setaria. These results were consistent with a lower level of infection and much greater root density in Setaria than in the other species. When Abutilon was grown in the presence of Setaria, mycorrhizal infection had no effect on Abutilon phosphorus content or dry weight. The depressive effect of Setaria on the response to inoculation in Abutilon was probably not caused by water soluble allelopathic chemicals from Setaria roots, but soil leachate from Abutilon plants did inhibit infection in other Abutilon plants. The data were consistent with the hypothesis that the very high root density and effective soil exploitation of Setaria reduced the benefit from mycorrhizal infection in Abutilon via phosphorus depletion in a large proportion of the available soil volume. Furthermore, even if mycorrhizal infection were capable of increasing phosphorus content of Abutilon in the presence of Setaria, the very high competitive ability of Setaria for nitrogen in the soil could have reduced the benefit of an enhanced phosphorus content. Carbon isotope ratios were reduced in Abutilon by mycorrhizal infection, indicating a possible reduction in water use efficiency.     

Positive association between mycorrhiza and foliar endophytes in Poa bonariensis, a native grass

The interaction between mycorrhiza and leaf endophytes (Neotyphodium sp.) was studied in three Poa bonariensis populations, a native grass, differing significantly in endophyte infection. The association between endophytes and mycorrhizal fungi colonisation was assessed by analysing plant roots collected from the field. We found that roots from endophyte-infected populations showed a significantly higher frequency of colonisation by mycorrhizal fungi and that soil parameters were not related to endophyte infection or mycorrhiza colonization. In addition, we did not observe significant differences in the number of AM propagules in soils of the three populations sites. We also report the simultaneous development of Paris-type and Arum-type mycorrhiza morphology within the same root systems of P. bonariensis. The co-occurrence of both colonisation types in one and the same root system found in the three populations, which differed in Neotyphodium infection, suggests that foliar endophytes do not determine AM morphology. The percentage of root length colonised by different types of fungal structures (coils, arbuscules, longitudinal hyphae and vesicles) showed significant and positive differences in arbuscular frequency associated with endophyte infection, whereas the much smaller amounts of vesicles and hyphal coils did not differ significantly.     

Presence of different arbuscular mycorrhizal infection patterns in roots of<Emphasis Type="Italic"> Lotus glaber</Emphasis> plants growing in the Salado River basin

Morphological types of arbuscular mycorrhizal (AM) fungi associated with Lotus glaber in sodic soils of the Salado River basin were studied. At least eight colonization patterns (IP) of AM fungi in roots of L. glaber were observed after 30 plants were analyzed. Arum- and Paris-type infection were found in the same plant species. This result supports the idea that AM morphology is not solely under plant control, but is also influenced by fungal identity. One infection pattern, presumably corresponding to Glomus intraradices, and a second, possibly assignable to Glomus tenue, were the most commonly found. Our results reinforce previous suggestions that G. intraradices is well adapted to sodic-saline conditions and may play a role in the resistance of L. glaber to these soils.     

New acidic chitinase isoforms induced in tobacco roots by vesicular-arbuscular mycorrhizal fungi

Summary Chitinase activities have been compared in tobacco roots (Nicotiana tabacum cv. Xanthi nc) infected by the pathogenic fungus Chalara elegans or three species of vesicular arbuscular mycorrhizal (VAM) fungi: Glomus versiforme, G. intraradix and G. fasciculatum, using native polyacrylamide gel electrophoresis (PAGE). All previously known acidic chitinase isoforms were stimulated in roots by the pathogenic fungus and by the VAM fungi, while two new acidic chitinase isoforms were specifically induced in response to the endomycorrhizal association. After separation in sodium dodecyl sulphate polyacrylamide denaturing gels (SDS-PAGE) under non-reducing conditions, the estimated apparent molecular mass for these additional acidic chitinase isoforms from VAM-colonized samples was 33 kDa, compared to 30 kDa for the main activity stimulated in C. elegans-infected root extracts.     

Polygalacturonase activity and location in arbuscular mycorrhizal roots of Allium porrum L.

Polygalacturonase activity and location were analysed in leek roots (Allium porrum L.) colonized by Glomus versiforme (Karst.) Berch, an arbuscular mycorrhizal (AM) fungus. Polygalacturonase activity in mycorrhizal roots did not differ quantitatively from that found in nonmycorrhizal roots on all of the four harvesting dates. Fractionation of mycorrhizal root extracts by ion-exchange chromatography showed that expression of polygalacturonase was specific to the mutualistic association. Immunofluorescence and immunogold experiments were carried out to locate the polygalacturonase in mycorrhizal roots using a polyclonal antibody raised against a Fusarium moniliforme endopolygalacturonase. Immunolabelling was observed all over the arbuscules (intracellular fungal structures) but particularly at the interface between the arbuscule and the plant membrane. Since pectins are located in this area, we suggest that polygalacturonase produced during the symbiosis could play a role in plant pectin degradation.     

Identification of Membrane-Associated Proteins Regulated by the Arbuscular Mycorrhizal Symbiosis

A sub-cellular proteomic approach was carried out to monitor membrane-associated protein modifications in response to the arbuscular mycorrhizal (AM) symbiosis. Membrane proteins were extracted from Medicago truncatula roots either inoculated or not with the AM fungus Glomus intraradices. Comparative two-dimensional electrophoresis revealed that 36 spots were differentially displayed in response to the fungal colonization including 15 proteins induced, 3 up-regulated and 18 down-regulated. Among them, seven proteins were found to be commonly down-regulated in AM-colonized and phosphate-fertilized roots. Twenty-five spots out of the 36 of interest could be identified by matrix assisted laser desorption/ionisation-time of flight and/or tandem mass spectrometry analyses. Excepting an acid phosphatase and a lectin, none of them was previously reported as being regulated during AM symbiosis. In addition, this proteomic approach allowed us for the first time to identify AM fungal proteins in planta.     

Expression of three <Emphasis Type="Italic">Arabidopsis</Emphasis> cytokinin oxidase/dehydrogenase promoter::GUS chimeric constructs in tobacco: response to developmental and biotic factors

Expression patterns of three Arabidopsis thaliana cytokinin oxidase/dehydrogenase promoter::GUS reporter fusions were investigated in tobacco plants. While cytokinin oxidase/dehydrogenase promoter 2 showed no expression in tobacco, the cytokinin oxidase/dehydrogenase promoters 3 and 4 were active in various tissues throughout development of the tobacco. Recently, the 1452 bp promoter region of AtCKX3 was reported as almost inactive in Arabidopsis. In contrast, the 1627 bp DNA fragment preceding the AtCKX3 coding region drove expression of the reporter GUS gene in various tobacco tissues. The promoter was mainly expressed in tobacco leaves and roots during early stages of development but also later in young flower buds as well as in pollen grains. The construct was particularly active before (hypocotyl region) and during (vascular system) lateral root initiation, supporting the idea of an inhibitory role of active cytokinins in the process of root initiation. The cytokinin oxidase/dehydrogenase promoter 4::GUS fusion in tobacco was shown to share some common (but weaker) expression patterns with promoter 3, namely in the leaves and pollen, but also conferred specific expression in tobacco root cap cells and trichomes. In addition, the response of cytokinin oxidase/dehydrogenase promoter::GUS reporter fusions to infection with the leafy gall-forming bacteria Rhodococcus fascians was examined. While an avirulent strain of R. fascians did not induce expression of any of the cytokinin oxidase/dehydrogenase promoters, the cytokinin oxidase/dehydrogenase promoter 3::GUS fusion was specifically induced at the site of infection when plants were challenged with a virulent strain of R. fascians, providing a possible explanation for the lack of significantly elevated cytokinin concentrations in tissues infected with virulent strains of R. fascians.This revised version was published online in August 2005 with some black and white figures replaced by coloured figures.     

The effect of carbohydrate on the development of a Cattleya hybrid in association with its mycorrhizal fungus

To investigate beneficial effects of mycorrhizal fungi to advanced leafy orchids, growth studies on the development of symbiotic seedlings of the orchid Cattleya (aclandiae x schoeffeldiana) x aclandiae were conducted in vitro over a period of 18 months using split plates with minerals and carbohydrates on one side and water agar on the other. Mycorrhizal infection and shoot and root growth of seedlings on the nutrient side were compared to growth on the water agar side with nutrient uptake by the orchid only possible via external mycorrhizal hyphae. Seed germination was followed by mycorrhizal infection and rapid development of protocorms on both nutrient and non-nutrient sides of the plates. With 0.5% starch, development of protocorms was sustained for a least 12 weeks, compared to only 6 weeks with 0.1% starch. Advanced protocorms with two small leaves and a smoll root were transferred at week 22 to new fungal plates. When harvested at week 43, plantlets on 0.5% starch (both nutrient and water agar sides) had 2.7 times the dry weight of plantlets on 0.1% starch. Shoot-root ratios were higher on the lower level of carbon. In all plantlets, mycorrhizal infection involved less than 5% of the root length. With zero, 0.1% or 0.5% starch, the roots were re-infected on transfer to fresh fungal plates but young roots that developed following the transfer stayed free of infection, Plantlets on 0.5% starch (nutrient and water agar side) after 18 months had longer roots than plantlets grown in the absence of starch or on 0.1% starch. Shoots were small but significantly larger on the nutrient side than on the water agar side, independent of the carbohydrate level. The shoot-root ratio was highest on the nutrient side with no starch present. In this latter case, plantlet development was steady but plantlets on the non-nutrient side developed slowly; thus there was little evidence of nutrient translocation by the mycorrhizal fungus from the nutrient to the non-nutrient side in the absence of carbohydrates. Mycorrhizal infection is discussed as a mechanism for heterotrophic carbon assimilation. In advanced leafy orchids of Cattleya, external carbon resulted in increased root growth, decreased shoot/root ratio and sometimes yellowish-green plantlets.     

Effects of mycorrhizae and chitin-hydrolysing microbes on Vicia faba

The effect of Streptomyces albovinaceus (S-22) and Bacillus sp. (B1) on the growth response, nodulation, nutrition and nitrogenase activities of faba bean (Vicia faba) varieties infected with Glomus mosseae under pot conditions in sterile soil amended with chitin was studied. The growth, nodulation, nutrients content and nitrogenase activity of mycorrhiza-treated plants of Giza-667 were significantly increased compared to untreated ones. Such increases were related to the increase in mycorrhizal root infection. Amendment of soil with chitin alone reduced the growth, nodulation, total nitrogen contents and nitrogenase activities of mycorrhiza-treated faba bean plants (Giza-667) compared to untreated plants. Inoculation of plants with S. albovinaceus or Bacillus sp. significantly increased the level of mycorrhizal roots infection, but addition of chitin to the soil in combination with Bacillus sp. reduced the mycorrhizal infection of faba bean roots. Highest phosphorus contents of faba bean Giza-667 were recorded after G. mosseae inoculation in the presence of all treatments. Similar results were observed for the other varieties. The microbial populations were significantly increased in rhizospheres amended with chitin. Such increases were not in response to the mycorrhizal inoculation. Generally, the microflora of faba bean rhizospheres was increased after treatment with G. mosseae in the absence of chitin amendment alone compared with non-mycorrhizal rhizospheres.     

Changes in root growth patterns of (Picea abies) spruce roots by inoculation with an ectomycorrhizal fungusPisolithus tinctorius and jasmonic acid treatment

Symbiosis between fungi and plant roots forming a mycorrhiza involves extensive interactions at the molecular level between both partners. The role of plant hormones in the regulation of mycorrhizal infection is not known to involve jasmonates. Their endogenous levels increase during pathogen attack; however, little has been done on their involvement in mycorrhizae. In our recent work, root growth patterns of 2-month-old spruce seedlings after inoculation withPisolithus tinctorius and/or jasmonic acid (JA) treatment were studied using a paper-sandwich technique. Changes in root length, the degree of branching, presence and length of root hairs, and infection parameters were followed using a stereomicroscope. The first mycorrhizal contact of hyphae with roots was significantly accelerated upon treatment with 0.5 M JA. Interactions between root hairs and fungal hyphae were seen by scanning electron microscopy. The multiplication of root hairs of non-mycorrhized seedlings treated with 5.0 M JA and changes of the root surface were observed by the same technique.