Search

Meeting the ever-increasing food demands of a growing global population while ensuring resource and environmental sustainability presents significant challenges for agriculture worldwide. Arbuscular mycorrhizal symbiosis (AMS) has emerged as a potential solution by increasing the surface area of a plant's root system and enhancing the absorption of phosphorus, nitrogen nutrients, and water. Consequently, there is a longstanding hypothesis that rice varieties exhibiting more efficient AMS could yield higher outputs at reduced input costs, paving the way for the development of Green Super Rice (GSR). Our prior research study identified a variant, OsCERK1DY, derived from Dongxiang wild-type rice, which notably enhanced AMS efficiency in the rice cultivar "ZZ35." This variant represents a promising gene for enhancing yield and nutrient use efficiency in rice breeding. In this study, we conducted a comparative analysis of biomass, crop growth characteristics, yield attributes, and nutrient absorption at varying soil nitrogen levels in the rice cultivar "ZZ35" and its chromosome single-segment substitution line, "GJDN1." In the field, GJDN1 exhibited a higher AM colonization level in its roots compared with ZZ35. Notably, GJDN1 displayed significantly higher effective panicle numbers and seed-setting rates than ZZ35. Moreover, the yield of GJDN1 with 75% nitrogen was 14.27% greater than the maximum yield achieved using ZZ35. At equivalent nitrogen levels, GJDN1 consistently outperformed ZZ35 in chlorophyll (Chl) content, dry matter accumulation, major nutrient element accumulation, N agronomic efficiency (NAE), N recovery efficiency (NRE), and N partial factor productivity (NPFP). The performance of OsCERK1DY overexpression lines corroborated these findings. These results support a model wherein the heightened level of AMS mediated by OsCERK1DY contributes to increased nitrogen, phosphorus, and potassium accumulation. This enhancement in nutrient utilization promotes higher fertilizer efficiency, dry matter accumulation, and ultimately, rice yield. Consequently, the OsCERK1DY gene emerges as a robust candidate for improving yield, reducing fertilizer usage, and facilitating a transition towards greener, lower-carbon agriculture. [ABSTRACT FROM AUTHOR]

Background: Arbuscular mycorrhizal (AM) symbiosis has been referred to as the mother of all plant root symbioses as it predated the evolution of plant roots. The AM research is a multidisciplinary field at the intersection of soil science, mycology, and botany. However, in recent decades the nature and properties of soils, in which the AM symbiosis develops and functions, have received less attention than desired. Scope: In this review we discuss a number of recent developments in AM research. We particularly cover the role of AM symbiosis in acquisition of phosphorus, nitrogen, heavy metals and metalloids, as well as water by plants from soil; mycorrhizal effects on plant nutritional stoichiometry and on the carbon cycle; the hyphosphere microbiome; so-called facultative mycorrhizal plants; explanations for lack of mycorrhizal benefit; common mycorrhizal networks; and arbuscular and ectomycorrhizal ecosystems. Conclusion: We reflect on what has previously been described as mycorrhizal 'dogmas'. We conclude that these are in fact generalisations on the AM symbiosis that are well supported by multiple studies, while admitting that there potentially is a geographical bias in mycorrhizal research that developed in temperate and boreal regions, and that research in other ecosystems might uncover a greater diversity of viable mycorrhizal and non-mycorrhizal strategies than currently acknowledged. We also note an increasing tendency to overinterpret data, which may lead to stagnation of some research fields due to lack of experiments designed to test the mechanistic basis of processes rather than cumulating descriptive studies and correlative evidences. [ABSTRACT FROM AUTHOR]

Jasmonates are believed to affect plant growth under stress conditions by improving the plant's antioxidant defense. They can also interfere in the mycorrhizal symbiosis. There is no detailed information available on the effect of methyl jasmonate (MeJ) on the physiology of barley; investigating the effect of this phytohormone on the relationships between fungus and plant, the combined effect of application of these two factors on the growth and physiology of the plant is a new perspective in sustainable agriculture. The present factorial experiment was conducted with three factors as a pot experiment. The plants were grown with inoculation with Funneliformis mosseae (AM) and application of 75 µM MeJ under drought stress conditions. Each of the treatments alone (+ MeJ − AM and − MeJ + AM) improved the plant growth under drought by fortifying the antioxidants defense. Although + MeJ − AM was found to be the most effective treatment under stress conditions, it caused some damages by reducing chlorophylls under non-stress conditions. Meanwhile, the highest plant growth under non-stress conditions belonged to − MeJ + AM. Application of MeJ along with AM reduced the damage caused by MeJ under non-stress conditions by taking advantage of the potential of mycorrhiza and improving symbiosis. However, under stress conditions, this treatment resulted in better plant growth compared to – MeJ + AM and – MeJ − AM with the positive effects of MeJ on the antioxidant system. Generally, due to the inevitable imposition of drought stress in the period of plant growth under normal conditions, it seems as if the combination of these treatments could be considered in future. Graphical preview of physiological and growth variations of barley under experimental factors. AM Arbuscular Mycorrhiza, MeJ Methyl jasmonate, + MeJ MeJ application, − MeJ non-MeJ application, + AM AM application, − AM non-AM application, Shoot Shoot dry weight, Root Root dry weight, Total Total dry weight, MDA Malondialdehyde, SOD Superoxide dismutase, POD peroxidase, PPO polyphenol oxidase. [ABSTRACT FROM AUTHOR]

The dynamic interactions of plants and arbuscular mycorrhizal fungi (AMF) that facilitate the efficient uptake of minerals from soil and provide protection from various environmental stresses (biotic and abiotic) are now also attributed to a third component of the symbiosis. These are the less investigated mycorrhizae helper bacteria (MHB), which constitute a dense, active bacterial community, tightly associated with AMF, and involved in the development and functioning of AMF. Although AMF spores are known to host several bacteria in their spore walls and cytoplasm, their role in promoting the ecological fitness and establishment of AMF symbiosis by influencing spore germination, mycelial growth, root colonization, metabolic diversity, and biocontrol of soil borne diseases is now being deciphered. MHB also promote the functioning of arbuscular mycorrhizal symbiosis by triggering various plant growth factors, leading to better availability of nutrients in the soil and uptake by plants. In order to develop strategies to promote mycorrhization by AMF, and particularly to stimulate the ability to utilize phosphorus from the soil, there is a need to decipher crucial metabolic signalling pathways of MHB and elucidate their functional significance as mycorrhiza helper bacteria. MHB, also referred to as AMF bioenhancers, also improve agronomic efficiency and formulations using AMF along with enriched population of MHB are a promising option. This review covers the aspects related to the specificity and mechanisms of action of MHB, which positively impact the formation and functioning of AMF in mycorrhizal symbiosis, and the need to advocate MHB as AMF bioenhancers towards their inclusion in integrated nutrient management practices in sustainable agriculture. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhiza (AM) is a widespread symbiosis between roots of the majority of land plants and Glomeromycotina fungi. AM is important for ecosystem health and functioning as the fungi critically support plant performance by providing essential mineral nutrients, particularly the poorly accessible phosphate, in exchange for organic carbon. AM fungi colonize the inside of roots and this is promoted at low but inhibited at high plant phosphate status, while the mechanistic basis for this phosphate-dependence remained obscure. Here we demonstrate that a major transcriptional regulator of phosphate starvation responses in rice PHOSPHATE STARVATION RESPONSE 2 (PHR2) regulates AM. Root colonization of phr2 mutants is drastically reduced, and PHR2 is required for root colonization, mycorrhizal phosphate uptake, and yield increase in field soil. PHR2 promotes AM by targeting genes required for pre-contact signaling, root colonization, and AM function. Thus, this important symbiosis is directly wired to the PHR2-controlled plant phosphate starvation response. Arbuscular mycorrhiza support plant phosphate uptake. Here Das et al. show that PHR transcription factors permit arbuscular mycorrhiza symbiosis by promoting gene expression related to symbiosis development and maintenance. [ABSTRACT FROM AUTHOR]

The role of mycorrhizal symbiosis as a control of the biogeochemical cycle of nitrogen in soils and in the nitrogen nutrition of plants is considered. The contribution of ericoid mycorrhiza (ErM) and ectomycorrhiza (EcM) to nitrogen (N) supply of host plants is well known, whereas the role of arbuscular mycorrhiza (ArM) is insufficiently understood. Exoenzymes released into the soil from the ErM and EcM mycelium favor the hydrolysis of high-molecular-weight N-containing organic compounds of plant litter and soils to or amino acids that are then transported toward plant roots and are absorbed by them. ArM-producing fungi have a limited capacity to release hydrolytic enzymes capable to decompose high-molecular-weight organic compounds into the soil (or do not have it at all). Therefore, they are specialized on the absorption of inorganic forms of N and amino acids appearing in the soil in the course of decomposition of high-molecular-weight N-containing compounds by saprotrophic microorganisms. The activity of hydrolytic exoenzymes and the role of mycorrhiza in the nitrogen nutrition of plants become more significant under conditions of the low supply with mineral N compounds and decrease upon the rise in availability of mineral N compounds. At the same time, mycorrhizal fungi and host plants may compete for the limited resource. The isotopic composition of N in plants (δ15N) and the fractionation of 15N isotope between the mycorrhizal fungi and host plants are considered indicative of the participation of mycorrhiza in the nitrogen nutrition of plants. [ABSTRACT FROM AUTHOR]

For decades, evolutionary plant biologists have been interested in how females reap a fitness advantage and are thus maintained in gynodioecious plants. Recent attention has focused on the role of multi-species interactions in the maintenance of females, wherein the role of arbuscular mycorrhizal fungi (AMF) is virtually unknown. AMF form symbiotic associations with plants, often resulting in enhanced nutrient acquisition and tolerance to biotic and abiotic stress. Depending on the degree to which females and hermaphrodites rely on their AMF partners, AMF could differentially affect plant tolerance to stress. We conducted a field experiment to examine (1) if females and hermaphrodites of the gynodioecious herb, Polemonium foliosissimum, differentially associate with AMF, and (2) if there was a difference in AMF colonization between the sexes after imposing stress by simulating herbivore damage. First, we compared mycorrhizal colonization between the sexes under ambient (i.e., undamaged) field conditions. Then, for a second set of plants, we simulated herbivory by clipping plants and compared mycorrhizal colonization, leaf phosphorus concentration [P], and fruit and seed production between clipped and control plants. Mycorrhizal colonization did not differ between sexes under ambient field conditions or under the stress imposed by clipping. Clipping did, however, influence both percent root length and vesicle colonization in a plant-size-dependent manner. Overall, colonization and vesicle number increased with plant size for clipped plants, but decreased with size for non-clipped plants. Leaf [P] did not differ between the sexes nor was influenced by clipping, and leaf [P] was not associated with mycorrhizal colonization. Furthermore, neither fruit set nor seed production was associated with mycorrhizal colonization. Our findings suggest that the sexes of P. foliosissimum do not differentially associate with nor differentially garner benefit from mycorrhizal fungi. However, a complete accounting of the costs and benefits of AMF for gynodioecious species must encompass the full life-history of the plant. [ABSTRACT FROM AUTHOR]

Plant-herbivore interactions and mycorrhizal symbiosis are important associations in grasslands that may interact due to their relationships with a common host plant and its resources. However, few studies have explored the effect of mycorrhizal symbiosis on plant-herbivore interactions. An understanding of the complex interactions between host plants, mycorrhizal fungi, and insect herbivores is enhanced by in situ examinations of the three parties acting simultaneously. The objective of this study was to quantify the effects of mycorrhizal symbiosis on insect herbivory and the host-plant community in tallgrass prairie. We used long-term mycorrhizal and fungicide-treated plots at Konza Prairie Biological Station (Manhattan, KS) to determine whether insect herbivory is altered by suppression of mycorrhizal fungi. Herbivory on plants in mycorrhizal control plots was greater than in fungicide-treated plots, and for one plant guild, C graminoids, the difference was significant. In fungicide-treated plots, plant diversity was significantly greater and herbivory was negatively correlated with plant species diversity. Differences in productivity of plant functional groups due to mycorrhizal symbiosis may be a key factor in patterns of insect herbivory. The results indicate that mycorrhizal symbiosis has diverse consequences, influencing the abundance and the quality of host plants in tallgrass prairie, as well as their responses to consumers. [ABSTRACT FROM AUTHOR]

The article discusses how DELLA protein complex controls the arbuscular mycorrhizal symbiosis in plants. Topics of discussion included were SLR1/DELLA, a repressor of gibberellic acid (GA) signaling, inhibition of mycorrhizal colonization by GA treatment in Pisum sativum, Oryzae sativa and mycorrhizal associated gene expression. Other topics were nutrient responses, light perception and signaling of several interacting hormones including auxin, ethylene and abscisic acid by DELLA.

Trends in the proportions of plants differently interacting with mycorrhizal fungi in the course of pasture digression have been analyzed in the steppe zone of the Southern Urals. Estimates of species richness and abundance of plant groups with different mycorrhizal status have been obtained by comparing original data on the structure of phytocenoses with published data on the ability of plant species to form mycorrhizae. It has been shown that the proportions and abundance of obligate mycorrhizal species decrease significantly in the course of digression, with consequent increase in those of species less dependent on or independent of symbiosis with fungi, i.e., facultative mycorrhizal or obligate nonmycorrhizal plants. [ABSTRACT FROM AUTHOR]

In the present study, we obtained in vitro dual cultures between the liverwort Plagiochasma rupestre and two arbuscular mycorrhizal (AM) fungi: Glomus intraradices and Glomus clarum. Four agarized culture media were tested for optimal growth of P. rupestre. Also, a description of the symbiotic association is provided. Plagiochasma rupestre gametophytes profusely grew axenically in MM with sucrose, and thalli were successfully subcultured under these growth conditions. Arbuscular mycorrhizal fungal hyphae colonized P. rupestre thalli through rhizoids or by forming appresoria in the ventral thallus cells. Arbuscules, mycelia and structures resembling intrathallic spores or vesicles were developed in the internal parenchymatic cells. The pattern of AM colonization in P. rupestre was very similar to the Paris-type. After 100 days of dual culture, the external mycelia of both AM fungal strains formed thousands of small viable spores, suggesting that P. rupestre in vitro culture could be a valuable tool for studying the biology of both symbiotic partners and conserving AM fungi in in vitro germplasm collections. [ABSTRACT FROM AUTHOR]

Symbioses between plants and beneficial soil microorganisms like arbuscular-mycorrhizal fungi (AMF) are known to promote plant growth and help plants to cope with biotic and abiotic stresses. Profound physiological changes take place in the host plant upon root colonization by AMF affecting the interactions with a wide range of organisms below- and above-ground. Protective effects of the symbiosis against pathogens, pests, and parasitic plants have been described for many plant species, including agriculturally important crop varieties. Besides mechanisms such as improved plant nutrition and competition, experimental evidence supports a major role of plant defenses in the observed protection. During mycorrhiza establishment, modulation of plant defense responses occurs thus achieving a functional symbiosis. As a consequence of this modulation, a mild, but effective activation of the plant immune responses seems to occur, not only locally but also systemically. This activation leads to a primed state of the plant that allows a more efficient activation of defense mechanisms in response to attack by potential enemies. Here, we give an overview of the impact on interactions between mycorrhizal plants and pathogens, herbivores, and parasitic plants, and we summarize the current knowledge of the underlying mechanisms. We focus on the priming of jasmonate-regulated plant defense mechanisms that play a central role in the induction of resistance by arbuscular mycorrhizas. [ABSTRACT FROM AUTHOR]

Aims: Nutrients play a key role in arbuscular mycorrhizal (AM) symbiosis. We quantified the response of AM symbiosis of seedlings and adult plants of Plantago lanceolata to fertilization under field conditions in managed grasslands differing in nutrient availability and soil moisture. Methods: The AM symbiosis was measured as the total extent of AM fungal colonization and frequency of arbuscules or vesicles, and as the relative proportions of morphotypes. We further examined the effects of the surrounding vegetation upon AM symbiosis. Results: Fertilization decreased total AM colonization and relative arbuscular frequency of the whole mycorrhizal community and of Acaulospora and 'fine endophyte' morphotypes in seedling roots, but it had no effect upon the mycorrhiza in adult plants. The decline in arbuscular frequency in seedling roots due to fertilization was greater at the sites with higher nutrient availability and lower N:P ratio. Seedlings surrounded by more forbs had a greater total AM colonization and higher vesicular frequency. Conclusions: Increased nutrient availability in the initial stages of seedling development has a prominent effect upon AM symbiosis development, but these effects seem to diminish over the long term, as evidenced by the results obtained for adult plants and from the limited effects of parameters characterizing long-term nutrient availability. [ABSTRACT FROM AUTHOR]

Exploitation of arbuscular mycorrhizal fungi may be an important approach for development of reduced-input agriculture. We discuss the use of linear models to analyze variation in mycorrhiza response among diverse plant varieties in order to assess the value of mycorrhizas. Our approach allows elimination of variation linked to differences in plant performance in the absence of mycorrhizas and the selection of plant lines that might harbor genetic variation of use to improve the mycorrhizal symbiosis in agriculture. We illustrate our approach by applying it to previously published and to novel data. We suggest that in dealing with a relative trait such as mycorrhiza effect, the choice of measure used to quantify the trait greatly affects interpretation. In the plant populations under consideration, we find evidence for a greater potential to increase mycorrhiza benefit than previously suggested. [ABSTRACT FROM AUTHOR]

Arsenic (As) contamination of soil and water is a global problem that impacts on many areas of biology. This review firstly covers aspects of soil chemistry and soil-plant interactions relevant to the ways plants take up As (particularly arsenate (As(V)) from aerobic soils, with especial attention to As-phosphorus (P) interactions. It then assesses the extent to which studies of plant As tolerance based on short-term uptake of As(V) from nutrient solutions can be extrapolated to longer-term growth in contaminated soil. Mycorrhizal symbioses are then highlighted, because they are formed by ~ 90% of higher plants, often with increased uptake of phosphate (Pi) compared with non-mycorrhizal (NM) counterparts. It is therefore likely that mycorrhizas influence As(V) uptake. Published work shows that arbuscular mycorrhizal (AM) plants (the most common mycorrhizal type) have higher P/As ratios than NM plants, and this would be expected to affect sensitivity to soil As. We discuss ways in which higher P/As selectivity might result from differential operation of P and As uptake pathways in AM compared with NM plants, taking into account new understanding of P uptake mechanisms. We also give suggestions for future research required to increase understanding of mechanisms of As(V) uptake, and its interactions with plant P. [ABSTRACT FROM AUTHOR]

Although mycorrhiza has been identified to be of major importance for plant nutrition and ecosystem stability, existing C- and N- simulation models on the ecosystem scale do not explicitly consider the feedbacks between ectomycorrhizal fungi and plants. We present a simple dynamic feedback model which allows estimating the main C- and N- flows between ectomycorrhizal fungi and tree roots in order to test the sensitivity of the system fungus-tree to environmental parameters and to assess the fungal contribution to plant N nutrition. Sensitivity tests carried out showed that the model responses to variations of model parameters, particularly with regard to N availability, are in agreement with published results from field and laboratory studies. However, there are still some processes and parameters which are not well constrained. Fungal N uptake rates and the ratio between mycelium, hartig net, and mantle biomass are parameters which significantly affect model results but for which published data are scarce or missing. Nevertheless, the model is already providing a platform to test our understanding of the importance of mycorrhiza for forest stand nutrition. Future coupling to a mechanistic ecosystem model will allow simulating the importance of mycorrhization for e.g. stand growth and C and N retention. [ABSTRACT FROM AUTHOR]

The relative importance of roots and AM-fungi on soil physical processes was investigated by controlling the presence of roots and AM fungi in pot experiments using a mycorrhiza-defective tomato mutant and a wild-type tomato ( Solanum lycopersicum L.). Root-Zone and Bulk Soil sections were established by splitting pots into two lengthwise halves using a nylon mesh that contained roots whilst allowing the free movement of fungal hyphae. Post-incubation microbial populations and fungal biomass were measured and related to soil stability, pore structure and water repellency. Unplanted controls consistently had the least fungal biomass, fatty acids, water-stable aggregates (WSA) and water repellency. Wild-type-planted treatments had significantly more WSA than mycorrhiza-defective treatments ( P < 0.01). Fluctuations in water content induced by transpiration caused significant changes in soil pore structure, measured using high-resolution X-Ray computer tomography. Porosity and mean pore size increased in soil aggregates from planted treatments, which had larger more heterogeneous pores than those in the unplanted soils. AM fungi accentuated soil stability. However, changes were not linked to repellency and fungal biomass. The presence of plants, regardless of AM fungi, appears to have the greatest impact on increasing soil stability. [ABSTRACT FROM AUTHOR]

The aims of the present study are to find out whether the effects of arbuscular mycorrhizal (AM) symbiosis on plant resistance to water deficit are mediated by the endogenous abscisic acid (ABA) content of the host plant and whether the exogenous ABA application modifies such effects. The ABA-deficient tomato mutant sitiens and its near-isogenic wild-type parental line were used. Plant development, physiology, and expression of plant genes expected to be modulated by AM symbiosis, drought, and ABA were studied. Results showed that only wild-type tomato plants responded positively to mycorrhizal inoculation, while AM symbiosis was not observed to have any effect on plant development in sitiens plants grown under well-watered conditions. The application of ABA to sitiens plants enhanced plant growth both under well-watered and drought stress conditions. In respect to sitiens plants subjected to drought stress, the addition of ABA had a cumulative effect in relation to that of inoculation with G. intraradices. Most of the genes analyzed in this study showed different regulation patterns in wild-type and sitiens plants, suggesting that their gene expression is modulated by the plant ABA phenotype. In the same way, the colonization of roots with the AM fungus G. intraradices differently regulated the expression of these genes in wild-type and in sitiens plants, which could explain the distinctive effect of the symbiosis on each plant ABA phenotype. This also suggests that the effects of the AM symbiosis on plant responses and resistance to water deficit are mediated by the plant ABA phenotype. [ABSTRACT FROM AUTHOR]

The review sums up the long experience of the authors and other researchers in studying the genetic system of garden pea ( Pisum sativum L.), which controls the development of nitrogen-fixing symbiosis and arbuscular mycorrhiza. A justified phenotypic classification of pea mutants is presented. Progress in identifying and cloning symbiotic genes is adequately reflected. The feasibility of using double inoculation as a means of increasing the plant productivity is demonstrated, in which the potential of a tripartite symbiotic system (pea plants-root nodule bacteria-arbuscular mycorrhiza) is mobilized. [ABSTRACT FROM AUTHOR]

Mycorrhiza is the main spatial and temporal linkage between different constituents in a forest ecosystem. The functional compatibility and stress tolerance of ectomycorrhizal types is species specific, and therefore the information on the ectomycorrhizal community structure can add to the understanding of processes in forest ecosystems and can also be applied as tools for bioindication of pollution stress in forest soils. We have studied the effects of pollution (N and S) on trees and forest soils by: (1) quantification of ECM types diversity as in situ indicators in forest stands, (2) determination and quantification of pollution-sensitive or -insensitive ECM types as passive monitors, (3) root growth and development of ECM on nonmycorrhizal spruce seedlings, planted at the studied sites (active monitors), and (4) ECM infection (a bioassay based on mycorrhizal inoculum potential) of seedlings in an experimental set-up as ex situ testers. ECM species richness for Norway spruce trees ( Picea abies) showed higher values in unpolluted sites than in polluted ones, while the differences were not significant for European beech trees ( Fagus sylvatica). As pollution-sensitive or -insensitive ECM species in spruce forests, we suggest Hydnum rufescens (sensitive) and Paxillus involutus (unsensitive). Mycorrhizal potential in Norway spruce seedlings as a bioassay for soil N and S pollution was effective, and is suggested as an additional, standardized and widely comparable system in bioindication of soil pollution. [ABSTRACT FROM AUTHOR]

Maritime pine ( Pinus pinaster) is the main tree cropping species in the Landes of Gascogne forest range in south western France. Soils are nutrient poor, sandy podzosols and site fertility is determined essentially by organic matter content and depth of water table, which is known to limit root growth. We hypothesised, with an ultimate goal of constructing a nutrient uptake model applicable to this region, that the organic top horizons together with the depth of the water table should be the most important parameters related to fine root distribution and presence of associated mycorrhiza. To test this hypothesis, we compared two adult Pinus pinaster stands, contrasting in depth of water table and soil fertility and evaluated fine roots (diameter ≤2 mm) of understory species and fine roots and ectomycorrhizal morphotypes of Pinus pinaster down to 1.2 m, using a soil corer approach. Total fine root biomass of Pinus pinaster was not significantly different between both sites (3.6 and 4.5 t ha−1 for the humid, respectively, dry site), but root distribution was significantly shallower and root diameter increased more with depth at the humid site, presumably due to more adverse soil conditions as related to the presence of a hardpan, higher amount of aluminium oxides and / or anoxia. Fine roots of Pinus pinaster represented only about 30% of total fine root biomass and 15% of total fine root length, suggesting that the understory species cannot be ignored with regards to competition for mineral nutrients and water. A comparison of the ectomycorrhizal morphotypes showed that the humid site could be characterised by a very large proportion of contact exploration types, thought to be more relevant in accessing organic nutrient sources, whereas the dry site had a significantly higher proportion of both long-distance and short-distance exploration types, the latter of which was thought to be more resistant to short-term drought periods. These results partly confirm our hypothesis on root distribution as related to the presence of soil mineral nutrients (i.e. in organic matter), point out the potential role of understory plant species and ectomycorrhizal symbiosis and are a valuable step in building a site-specific nutrient uptake model. [ABSTRACT FROM AUTHOR]

High concentrations of heavy metals (HM) in the soil have detrimental effects on ecosystems and are a risk to human health as they can enter the food chain via agricultural products or contaminated drinking water. Phytoremediation, a sustainable and inexpensive technology based on the removal of pollutants from the environment by plants, is becoming an increasingly important objective in plant research. However, as phytoremediation is a slow process, improvement of efficiency and thus increased stabilization or removal of HMs from soils is an important goal. Arbuscular mycorrhizal (AM) fungi provide an attractive system to advance plant-based environmental clean-up. During symbiotic interaction the hyphal network functionally extends the root system of their hosts. Thus, plants in symbiosis with AM fungi have the potential to take up HM from an enlarged soil volume. In this review, we summarize current knowledge about the contribution of the AM symbiosis to phytoremediation of heavy metals. [ABSTRACT FROM AUTHOR]

In this work we evaluate whether the effect of ectomycorrhiza in the early developmental stages of symbiosis establishment is detrimental or beneficial to plant productivity and whether this effect is dependent on either N nutrition or plant age. Groups of Pinus pinaster L. plants with different ages and nutritional status were inoculated with alive or dead Pisolithus tinctorius. The plants were fed with either 1.9 m M or 3.8 m M ammonium as N source. Ectomycorrhiza establishment was monitored until 1 month after the inoculation through daily chlorophyll a fluorescence measurements and the analysis of fast fluorescence kinetics O-J-I-P, biomass increment and photosynthesis. Our results show that plants react differently to ectomycorrhiza formation depending on their age (stage of development, leaf area), their initial nutritional status, and the amount of nitrogen supplied. Mycorrhiza formation was found to constitute a stress depending on the plants’ age. Increased availability of N softened or eliminated the negative impact of mycorrhiza formation. Only younger plants eventually developed a higher net photosynthesis rate when mycorrhizal. It is concluded that ectomycorrhiza formation may have a detrimental rather than a beneficial effect on plants’ productivity during their establishment and early developmental stages, and that this depends on the amount of N available to the plant, on the nutritional status and on the age of the plant. Chlorophyll a fluorescence measurements proved to be a non-destructive, non-invasive and reliable tool able to identify the first signals of plant-mycorrhiza fungi interactions. [ABSTRACT FROM AUTHOR]

Autoregulatory mechanisms have been reported in the rhizobial and the mycorrhizal symbiosis. Autoregulation means that already existing nodules or an existing root colonization by an arbuscular mycorrhizal fungus systemically suppress subsequent nodule formation/root colonization in other parts of the root system. Mutants of some legumes lost their ability to autoregulate the nodule number and thus display a supernodulating phenotype. On studying the effect of pre-inoculation of one side of a split-root system with an arbuscular mycorrhizal fungus on subsequent mycorrhization in the second side of the split-root system of a wild-type soybean (Glycine max L.) cv. Bragg and its supernodulating mutant nts1007, we observed a clear suppressional effect in the wild-type, whereas further root colonization in the split-root system of the mutant nts1007 was not suppressed. These data strongly indicate that the mechanisms involved in supernodulation also affect mycorrhization and support the hypothesis that the autoregulation in the rhizobial and the mycorrhizal symbiosis is controlled in a similar manner. The accumulation patterns of the plant hormones IAA, ABA and Jasmonic acid (JA) in non-inoculated control plants and split-root systems of inoculated plants with one mycorrhizal side of the split-root system and one non-mycorrhizal side, indicate an involvement of IAA in the autoregulation of mycorrhization. Mycorrhizal colonization of soybeans also resulted in a strong induction of ABA and JA levels, but on the basis of our data the role of these two phytohormones in mycorrhizal autoregulation is questionable. [ABSTRACT FROM AUTHOR]

A community of arbuscular mycorrhizal (AM) fungi was investigated in a warm-temperate deciduous broad-leaved forest using a molecular analysis method. Root samples were obtained from the forest, and DNA was extracted from the samples. Partial 18S rDNA of AM fungi were amplified from the extracted DNA by polymerase chain reaction using a universal eukaryotic primer NS31 and an AM fungal-specific primer AM1. After cloning the PCR products, 394 clones were obtained in total, which were divided into five types by restriction fragment length polymorphism (RFLP) with HinfI, RsaI, and Hsp92II. More than 20% of the clones were randomly selected from each RFLP type and sequenced. Phylogenetic analysis showed that all the obtained clones belonged to Glomus but could not be identified at species level. Topsoil of the forest containing plant roots was inoculated to nonmycorrhizal seedlings of indigenous woody plants, Rhus javanica var. roxburghii and Clethra barvinervis, to introduce the community of AM fungi into the seedlings. Among these five RFLP types, four types were detected from both seedlings, which indicates that the AM fungal community in the forest root samples was introduced at least partly into the seedlings. Meanwhile, an additional four types that were not found in the forest root samples were newly detected in the seedlings, these types were closely related to one another and close to G. fasciculatum or G. intraradices. It is expected that a community of indigenous diverse AM fungi could be introduced into target fields by planting these mycorrhizal seedlings. [ABSTRACT FROM AUTHOR]

To investigate the occurrence of arbuscular mycorrhizas (AM) and their morphological types, four Athyrium yokoscense and five A. niponicum individuals were collected at a lead-contaminated site. Three of the A. yokoscense and four of the A. niponicum formed AM structures. However, the percentage of AM formation within both species differed significantly among individuals. Morphological types of most AM structures were the Paris-type, except for one A. yokoscense that formed both Paris-type and Arum-type-like structures in different parts of the same root section. These results demonstrate that the two Athyrium species form AM associations in lead-contaminated soil. [ABSTRACT FROM AUTHOR]

Abstract A. B. Franks observations and hypotheses about mycorrhizae in 1885 flew in the face of conventional thinking of the time. He reported that what we now term ectomycorrhizae were widespread on root systems of many woody plant species in a great diversity of habitats and soils. He hypothesized that mycorrhizae represent a pervasive mutualistic symbiosis in which fungus and host nutritionally rely on each other; that the fungus extracts nutrients from both mineral soil and humus and translocates them to the tree host; and that the tree, in turn, nourishes the fungus. Initially opposed by much of the scientific community, nearly all of Franks major hypotheses have since been unequivocally demonstrated, although many decades were required to achieve conclusive evidence. Nonetheless, the revolution in thinking about plant and fungal evolution, ecology and physiology generated by Frank is still in the process of acceptance by much of the scientific community, 120years and tens of thousands of scientific papers since he coined the term mycorrhiza. The reasons for this extraordinary lag time in themselves present an intriguing research subject. [ABSTRACT FROM AUTHOR]

The functioning of the plant-mycorrhiza system depends on interactions with other organisms, including saprotrophic (ST) soil fungi. The interactions between mycorrhizal and ST fungi are likely affected by fungivorous soil animals, such as Collembola. In a two-factorial laboratory experiment lasting for 30 weeks we assessed the effects of an arbuscular mycorrhizal fungus (Glomus mosseae) and Collembola (Protaphorura fimata, Heteromurus nitidusandFolsomia candida) on the community composition of ST microfungi in soil planted with the invasive grassCynodon dactylon. The presence of mycorrhiza substantially reduced total plant biomass and reduced N and P availability to the soil microflora, though these effects were less pronounced in the presence of Collembola. The density of Collembola was high (corresponding to about 2×105 individuals m-2) and was not affected by the presence ofG. mosseae. In spite of the large amount of mycorrhizal mycelium in soil, it contributed little to Collembola nutrition. The presence of mycorrhiza strongly affected the community structure of ST soil fungi. In particular, mycorrhiza reduced the relative abundance ofTrichoderma harzianumandExophialasp., but increased the abundance ofRamichloridium schulzeriand several sterile forms. However, the difference between fungal communities in mycorrhizal and non-mycorrhizal treatments was much more pronounced in the presence of Collembola. Presumably, the intense grazing by Collembola destabilized the ST fungal community, thereby making it more susceptible to the influence ofG. mosseae. These results document for the first time that fungal feeding soil invertebrates can significantly affect the interactions between mycorrhizal fungi and ST soil microorganisms. [ABSTRACT FROM AUTHOR]

No abstract available. [ABSTRACT FROM AUTHOR]

Abstract Colonization by arbuscular mycorrhizal (AM) fungi was investigated in cucumber (Cucumis sativus), tomato (Lycopersicon esculentum) and Clethra barbinervis (Ericales) grown in field-collected soil known from previous studies to generate Paris-type arbuscular mycorrhizae in C. barbinervis. Spores of Paraglomus, Acaulospora, Glomus, and Gigaspora were found in the soil. Formation of hyphal coils and arbusculate coils of Paris-type mycorrhizae and of arbuscules of Arum-type mycorrhizae in roots raised in this soil in the growth chamber were compared with the detection of DNA of AM fungi from the same root systems using Glomales-specific primers. Only Paris-type mycorrhizae with extensive arbusculate coils developed in C. barbinervis, but cucumber and tomato developed both Paris- and Arum-types in the same root systems. Glomaceae and Archaeosporaceae and/or Paraglomaceae were detected strongly in the DNA from both cucumber and tomato roots, in which Arum-type mycorrhizae were observed. In contrast, DNA of Glomaceae was detected more sparingly in C. barbinervis, in which Paris-type mycorrhizae dominated. Acaulosporaceae and Gigasporaceae were strongly detected in the DNA from both C. barbinervis and tomato, whereas they were more weakly detected in cucumber. These results indicate that the morphology of colonization is strongly influenced by the selection of fungi to colonize the host plant from among those in the soil environment. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizae affect grassland plant community composition and host plant nutrient uptake, and can mediate shifts in competitive outcome between plant species.Centaurea maculosa, an invasive forb from Eurasia, dominates more than 4 million hectares in the Rocky Mountain region of North America. We examined the role of AM for phosphorus (P) acquisition from a distant source forC. maculosaandFestuca idahoensis, a native bunchgrass. Plants were grown individually in pots divided by a barrier that either excluded plant roots and AM hyphae, or only plant roots. In the half of the pot without a plant, 1 of 3 P treatments was applied: no P, phosphate rock (PR) or triple superphosphate (TSP), applied at a rate of 144 mg P kg-1 soil. After 14 weeks of growth,C. maculosawas twice as large asF. idahoensis, and neither species’ biomass was affected by barrier type. Phosphorus fertilizer, and especially PR, moved across the barrier to the plant side of the pot. Tissue P concentration forC. maculosawas highest with the PR treatment, and was not affected by the barrier type. In contrast,F. idahoensistissue P concentration did not vary with barrier or P treatments. There was more AM extra radical hyphae (ERH) associated withC. maculosathanF. idahoensis, suggesting thatC. maculosaprovides more carbon for the AM fungi, resulting in greater ERH production, ERH soil exploration and potential for soil nutrient pool exploitation. Although not tested in this study, differences between host plants may be the result of different physiological characteristics of the host plant or differences in AM fungal species that colonize the invader, with different fungal species accessing P from different distances. [ABSTRACT FROM AUTHOR]

This is not a review paper in the traditional sense, of which there are many. Three of the most influential reviews that summarized well some of the ?older? literature include those by Nicolson (1967), Gerdemann (1968) and Mosse (1973). Instead, in this brief and incomplete work, we attempt to show the historical development of research on arbuscular mycorrhizas. We owe much to those who have written other historical accounts, including Rayner (1926?1927), Trappe and Berch (1985), Mosse (1985), Schenck (1985), Harley (1991) and Allen (1996), but the contents of this work naturally reflect our own ignorance, interests and biases. It was often difficult to distinguish between the historical and the contemporary, and we did not use any specific cutoff date in making this distinction. The degree to which we include ?contemporary? literature was determined by our own assessment of its connectedness to older literature. In any case, we hope this will be of some interest to those of you who study the arbuscular mycorrhiza, and that it will serve the purpose of providing what we consider to be an important historical context for current researchers. We wish you good fortune in your research. [ABSTRACT FROM AUTHOR]

In northern boreal forests, podzolic soils prevail that comprise of a distinct upper organic humus/mor (O) horizon that is supported by underlying eluvial (E) and illuvial (B) mineral horizons. The dominant tree species, Scots pine (Pinus sylvestris L.), is known to be highly dependent on root symbiosis with ectomycorrhizal fungi that develop in constituent podzol horizons for growth in these nutrient limited soils. The aim of this microcosm-based study was a quantification of photosynthetically fixed 14C allocation, following standard pulse-feeding of 7-month-old Scots pine seedling shoots, to respective root and mycorrhizosphere compartments that developed in the reconstructed podzol (O, E and B) profile. Biomass of roots and mycorrhizas decreased with increasing soil depth but no soil origin, control forest vs. clear-cut area, related differences were observed. Similarly, no major soil origin- or podzol horizon-related differences in categorised ectomycorrhizal morphotypes and number of mycorrhizas, in relation to pooled root and mycorrhiza biomass, were detected. However, the total recovery of 14C-label was significantly higher in clear-cut soil microcosms compared to control counterparts. A significant finding was equivalent 14C-carbon allocation to roots and ectomycorrhizas in all three major, organic and mineral, podzol profile horizons studied. These carbon allocation data provide additional support for direct (or indirect) roles of roots and symbiotic mycorrhizal fungi in mineral weathering and biodegradation of organic ligands that are central for plant acquisition of growth limiting nutrients and the podzolization process in boreal forest ecosystems. [ABSTRACT FROM AUTHOR]

Four Musa cultivars, differing in nematode susceptibility, were selected to study their relative mycorrhizal dependency and to study the interaction between the arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and two migratory endoparasitic nematodes, Radopholus similis and Pratylenchus coffeae. Mycorrhization with G. mosseae resulted in significantly better plant growth, even in the presence of R. similis and P. coffeae. No differences in relative mycorrhizal dependency (RMD) were observed among the four cultivars. G. mosseae suppressed nematode population build-up in Grande Naine and Pisang Jari Buaya. Only in the case of R. similis (Indonesian population) in Pisang Jari Buaya, no significant suppression was observed. In the case of P. coffeae, the AMF reduced the damage in the roots, caused by the nematodes. For R. similis, no reduction of damage was observed. In all, except one experiment, the frequency of the mycorrhizal colonisation was negatively affected by the nematodes. [ABSTRACT FROM AUTHOR]

Mycorrhizas are the most important mutualistic symbioses on earth. The most prevalent type are the arbuscular mycorrhizas (AMs) that develop between roots of most terrestrial plants and fungal species of the Zygomycota. The AM fungi are able to grow into the root cortex forming intercellular hyphae from which highly branched structures, arbuscules, originate within cortex cells. The arbuscules are responsible for nutrient exchange between the host and the symbiont, transporting carbohydrates from the plant to the fungus and mineral nutrients, especially phosphate, and water from the fungus to the plant. Plants adapt their phosphate uptake to the interaction with the AM fungus by synthesis of specific phosphate transporters. Colonization of root cells induces dramatic changes in the cytoplasmic organization: vacuole fragmentation, transformation of the plasma membrane to a periarbnscular membrane covering the arbnscule, increase of the cytoplasm volume and numbers of cell organelles, as well as movement of the nucleus into a central position. The plastids form a dense network covering the symbiotic interface. In some of these changes, microtubules are most likely involved. With regard to the molecular cross talk between the two organisms, a number of phytohormones (cytokinins, abscisic acid, jasmonate) as well as various secondary metabolites have been examined: (i) Jasmonates occur at elevated level, which is accompanied by cell-specific expression of genes involved in jasmonate biosynthesis that might be linked to strong carbohydrate sink function of AM roots and induced defense reactions; (ii) apocarotenoids (derivatives of mycorradicin and glycosylated cyclohexenones) accumulate in most mycomhizal roots examined so far. Their biosynthesis via the nonmevalonate methylerythritol phosphate (MEP) pathway has been studied resulting in new insights into AMspecific gene expression and biosynthesis of secondary isoprenoids. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi are mutualists with plant roots that are proposed to enhance plant community diversity. Models indicate that AM fungal communities could maintain plant diversity in forests if functionally different communities are spatially separated. In this study we assess the spatial and temporal distribution of the AM fungal community in a wet tropical rainforest in Costa Rica. We test whether distinct fungal communities correlate with variation in tree life history characteristics, with host tree species, and the relative importance of soil type, seasonality and rainfall. Host tree species differ in their associated AM fungal communities, but differences in the AM community between hosts could not be generalized over life history groupings of hosts. Changes in the relative abundance of a few common AM fungal species were the cause of differences in AM fungal communities for different host tree species instead of differences in the presence and absence of AM fungal species. Thus, AM fungal communities are spatially distinguishable in the forest, even though all species are widespread. Soil fertility ranging between 5 and 9 Mg/ha phosphorus did not affect composition of AM fungal communities, although sporulation was more abundant in lower fertility soils. Sampling soils over seasons revealed that some AM fungal species sporulate profusely in the dry season compared to the rainy season. On one host tree species sampled at two sites with vastly different rainfall, relative abundance of spores from Acaulospora was lower and that of Glomus was relatively higher at the site with lower and more seasonal rainfall. [ABSTRACT FROM AUTHOR]

Abstract Two genetically related strains of Tuber borchii Vittad. (1BO and 43BO) produce mycorrhizas with Tilia platyphyllos Scop. with a different degree of efficiency. The aim of this work was to characterize the morphology of the fungal symbiotic structures in order to examine potential relationships between the anatomical traits of the mycorrhiza, the mycorrhizal capacities of the fungal strains and their effect on the host plants. Some morphological features of mantle hyphae (small size, intense staining, vacuolization, abundance of mitochondria) led to a mantle with morphological features that were isolate-specific. There were unexpected differences, at least under our experimental conditions: 1BO strain mantle cells were larger, less reactive to staining, more highly vacuolated and poorer in mitochondria than those of 43BO. These features were found throughout the mantle in 1BO, while the inner mantle hyphae of 43BO were significantly smaller and more intensely stained than the outer cells. In the 43BO strain there was a positive relation between these features and higher infectivity (evaluated as percentage of mycorrhizal tips) as well as a slightly more effective stimulation of plant growth. These observations suggest that genetically related truffle strains produce mycorrhizas with different morphologies, which may be related to a more efficient response of the host plant to inoculation. [ABSTRACT FROM AUTHOR]

Abstract. With the increasing awareness of the significance of mycorrhizas, research is focusing on studies to elucidate the contribution of the symbiosis to ecosystem dynamics. In this sense, molecular biology has acquired great significance. PCR/RFLP techniques were adapted to characterize ectomycorrhizal fungi associated with Eucalyptus grandis. The ITS region of the fungal rDNA from pure cultures and from of mycorrhizas synthesized in vitro was amplified. Primers NSA3/NLC2 were used followed by a nested reaction with primers ITS1F/NLB3. Amplicons were then digested with the enzymes MboI, HinfI and TaqI. Amplification resulted in a 1,000-bp fragment for basidiomycetes and a 1,500 bp fragment for Cenococcum geophillum (an ascomycete). There was no amplification of the plant DNA. The enzymes MboI and HinfI were more effective than TaqI, resulting in patterns of two to five fragments allowing the identification of the isolates both in culture and in mycorrhizas. HinfI allowed greater differentiation among the isolates and a higher number of polymorphisms. Restriction with TaqI resulted in too many fragments. Amplification efficiency for the fungal DNA was 64% in culture and 87% in mycorrhizas. The modified methodology represents a valuable tool to complement traditional approaches in ecosystem studies. [ABSTRACT FROM AUTHOR]

The aim of the study was to assess the effect of the mycorrhizosphere of A. tortillis spp. raddiana mycorrhized with Glomus intraradices on the root nodulation by Sinorhizobium terangae (ORS 1009) and/or Mesorhizobium plurifarium (ORS 1096) in two different culture substrates (sandy soil and sand). The endomycorrhizal fungus only stimulated plant growth in the sandy soil. Moreover, arbuscular mycorrhizal infection enhanced the nodulation process in both culture substrates. Beside the stimulatory effects of the mycorrhizosphere on both rhizobia development, fungal symbiosis induces two different dynamics of each bacterial strains in the sand-grown plants. These results suggest specific relationships could occur during the development of the tripartite symbiosis, at physiological and molecular level. From a practical point of view, the role of arbuscular mycorrhizas in improving nodulation and N2 fixation is universally recognized. The fungal symbiosis could modify the development of bacterial inoculants along the root systems. This effect is of particular interest in the controlled inoculation of selected rhizobia. [ABSTRACT FROM AUTHOR]

Symbiotic mycorrhizal fungi play an important role in the absorption of soil nutrients and water by most plants. It has been suggested that hydraulically lifted water might maintain the integrity of the external mycorrhizal mycelium during drought. We tested this hypothesis in the obligately mycorrhizal species, coast live oak (Quercus agrifolia), using a microcosm system that separated the effects of hydraulic lift in roots from those in the external mycelium. Mycorrhizal oak seedlings were established in microcosms comprising three discrete compartments for (1) upper roots, (2) tap roots, and (3) external fungal mycelium. Eight months after planting, a drought treatment was initiated: irrigation to the upper root and fungal chambers was terminated and only irrigation to the taproot compartment was maintained. After 3, 12, 30, 50, 70 and 80 days of drought, tracers were injected into the taproot compartment at dusk. At dawn the following morning, mycorrhizal hyphae (EM and AM) and spores (AM) in upper root and fungal compartments were extensively labeled with the tracers. In contrast, no labeling was observed when tracers were injected into the taproot compartment during daytime. Nocturnal water translocation from plant to mycorrhizal fungi occurred in association with hydraulic lift. Saprotrophic/parasitic fungi in the microcosms were not labeled, suggesting a direct water transfer from plants to their mycorrhizal mutualists and not to other fungi in the soil. Even after prolonged drought (70–80 days), mycorrhizal hyphae persisted in soils with water potential values as low as –20 MPa. Maintaining mycorrhizal activity through direct water translocation could potentially improve the nutrient status of deep-rooted plants during periods when the fertile upper soil is dry. [ABSTRACT FROM AUTHOR]

Examines the structure, function and responses of root endodermis and exodermis to the environment. Nature of root endodermis and exodermis; Role of the Casparian bands of the endodermis; Effect of endodermis on mycorrhizae.

We investigated the interactive effects of soil phosphorus (P) heterogeneity, plant density and mycorrhizal symbiosis on plant growth and size variability of Trifolium subterraneum. We set up mesocosms (trays 49×49 cm and 12 cm deep) with the same amount of available P, but distributed either homogeneously or heterogeneously, in randomly arranged cells (7×7 cm each) with high or low available P. The trays were planted with either 1 or 4 seedlings of T. subterraneum per cell. Half of the trays were inoculated with spores of the mycorrhizal fungus Gigaspora margarita. We harvested the plants when leaves just started to overlap, 8 weeks after planting. Plants growing in high P cells had the lowest percentage infection, but the highest mean shoot and root biomass and root length. The mean size of the plants in each cell was determined mainly by local P concentration. However, in plants growing in high density, low P cells, ca. 20% of the variability in plant biomass was explained by the number of adjacent cells with high P. Patchy trays had the highest total shoot biomass, independently of mycorrhizal infection or plant density. Inoculated trays (M) had higher total shoot biomass and relative competition intensity (measured as reduction in plant biomass due to increased density) than non-inoculated trays (NM). Plant density reduced the plant response to mycorrhizal infection, and its effect was independent of P distribution. All populations growing in patchy trays, and low density mycorrhizal ones, had the highest plant-size inequality, presumably because patchy distribution of P and mycorrhizal infection increased competitive asymmetry. We conclude that mycorrhizal symbiosis has the potential to strongly influence plant population structure when soil nutrient distribution is heterogeneous because it promotes pre-emption of limiting resources. [ABSTRACT FROM AUTHOR]

The entry of calcium and magnesium from external sources into mycorrhizal roots of 3-year-old Norway spruce trees (Piceaabies [L.] Karst.) was monitored. Roots of intact plants were exposed for various periods of time, ranging from 2 min to 48 h, to nutrient solutions which contained the stable-isotope tracers 25Mg and 44Ca. After labelling, samples of roots were excised from the plants, shock-frozen, cryosubstituted and embedded. The resulting isotope composition in this material was analysed by a laser-microprobe-mass-analyser (LAMMA) at relevant positions within cross-sections of the roots. For both elements, we determined (i) the fractions of the isotopes originating from the plant prior to labelling, and (ii) the fraction of isotopes originating from the corresponding tracer that penetrated into the root. Both divalent cations rapidly penetrated across the cortical apoplast and reached the endodermis. After 2 min of exposure to the labelling solution, an initial transient gradient of the tracers could be observed within the root cortex. Subsequently, calcium as well as magnesium equilibrated between the apoplast of the entire cortex and the external tracer with a half-time, t1/2, of about 3 min. In contrast, the kinetics of radial movement into the vascular stele showed a delay with a t1/2 of 100–120 min. We take this as strong evidence that there exists a free apoplastic path for divalent cations in the cortex and that the endodermis is a major barrier to the further passage of Mg and Ca into the xylem. While 25Mg in the labelling solution exchanged rapidly with Mg in the cortical apoplast, the exchange across the plasma membrane with Mg present in the protoplasm of the same cortical cells was almost 2 orders of magnitude slower. The kinetics of Ca and Mg entry at +6 °C were similar to those obtained at a root temperature of +22 °C. [ABSTRACT FROM AUTHOR]

Microbial communities in the mycorrhizosphere (i.e. in the small volume of soil immediately surrounding a mycorrhizal root) actively interact with the establishment and functioning of the mycorrhizal symbiosis. Examples of competitive and mutualistic interactions are given, and are discussed in the light of recent observations and experimental results. The significance of biological interactions in the mycorrhizosphere is considered from the standpoints of plant ecology and of practical application. [ABSTRACT FROM AUTHOR]

Monotropoid mycorrhiza formation and its morphological characteristics on an achlorophyllous plant, Monotropastrum globosum f. roseum, were investigated. The forma formed typical monotropoid mycorrhizae, indicating that the forma is myco-heterotrophic. Morphological characteristics of the mycorrhizae and root systems of the forma were quite different from those of Monotropastrum globosum, suggesting that further investigation on host specificity and the phylogeny of the plants should be conducted. [ABSTRACT FROM AUTHOR]

Presents a broad phylogenetic analysis of mycorrhizal and free-living homobasidiomycetes or mushroom-forming fungi. Results, which indicate that mycorrhizal symbionts with diverse plant hosts have evolved repeatedly from saprotrophic precursors, but that there have also been multiple reversals to a free-living condition; Suggestion that mycorrhizae are unstable, evolutionarily dynamic associations.

This month's Genome Watch focuses on the genome sequences of several fungal species with distinct and varied lifestyles. These range from a saprophytic existence in dung to symbiotic mycorrhizal associations with plant roots to parasitism of grain. Analyses of the genome sequences reveal how evolution has played a crucial part in shaping the genetic make-up of these fungi to enable them to thrive within their microenvironments. [ABSTRACT FROM AUTHOR]

This article reports that plant roots release potent molecules that activate symbiotic fungi and initiate a harmonious relationship. Of all the fungi, it is a group known as the Glomeromycota that arguably has the greatest claim to public notice. The reason is that its members form symbiotic associations known as arbuscular mycorrhiza with plant roots, and without this symbiosis flora of this planet would have a very different constitution. But once the fungal hyphae sense the presence of a potential host, they branch and proliferate profusely; this probably increases the chance of contact with the root and subsequently infecting. In another symbiotic relationship--that between legume roots and nitrogen-fixing, chemical communication also occurs before infection.

The article discusses the study "Convergent Losses of Decay Mechanisms and Rapid Turnover of Symbiosis Genes in Mycorrhizal Mutualists," by researcher A. Kohler published in the journal "Nature Genetics" to analyze the evolution of mycorrhizal fungi.

The article discusses research on the symbiotic relationship between host cells and fungi. It references the studies "A secreted fungal effector of Globus intraradices promotes symbiotic biotrophy" by S. Kloppholz, H. Kuhn, and N. Requena and "A secreted effector protein of Laccaria bicolor is required for symbiosis development" by J. Plett. and collegues in the 2011 issue of "Current Biology." It states that secreted fungal effectors changes the host cells which allows mycorrhizae formation.