The use of the fluorescent dye, 3,3'-dihexyloxacarbocyanine iodide, for selective staining of ascomycete fungi associated with liverwort rhizoids and ericoid mycorrhizal roots

A detection method for neuronal death indicates abnormalities in intracellular membranous components in neuronal cells that underwent delayed death

Acute neuronal degeneration is always preceded under the light and electron microscopes by a stage called microvacuolation, which is characterized by a finely vacuolar alteration in the cytoplasm of the neurons destined to death. In this study, we reported a method for detecting neuronal death using two membrane-bound dyes, rhodamine R6 and DiOC₆(3), which may be associated with the so-called microvacuolation. This new method produced a spatiotemporally similar staining pattern to Fluoro-Jade B in kainic acid-damaged brains in mice. Further experiments showed that increased staining of rhodamine R6 and DiOC₆(3) was observed only in degenerated neurons, but not in glia, erythrocytes, or meninges. Different from Fluoro-Jade-related dyes, rhodamine R6 and DiOC₆(3) staining is highly sensitive to solvent extraction and detergent exposure. Staining with Nile red for phospholipids and filipin III for non-esterified cholesterol supports that the increased staining of rhodamine R6 and DiOC₆(3) might be associated with increased levels of phospholipids and free cholesterol in the perinuclear cytoplasm of damaged neurons. In addition to kainic acid-injected neuronal death, rhodamine R6 and DiOC₆(3) were similarly useful for detecting neuronal death in ischemic models either in vivo or in vitro. As far as we know, the staining with rhodamine R6 or DiOC₆(3) is one of a few histochemical methods for detecting neuronal death whose target molecules have been well defined and therefore may be useful for explaining experimental results as well as exploring the mechanisms of neuronal death. (250 words).

Expansion of Internal Hyphal Growth in Fusarium Head Blight-Infected Grains Contributes to the Elevated Mycotoxin Production During the Malting Process

Fusarium head blight (FHB) and the occurrence of mycotoxins is the largest food safety threat to malting and brewing grains. Worldwide surveys of commercial beers have reported that the trichothecene mycotoxin deoxynivalenol (DON) is the most frequent contaminant in beer. Although the DON content of grain generally declines during steeping due to its solubilization, Fusarium spp. can continue to grow and produce DON from steeping through the early kilning stage of malting. DON present on malt is largely extracted into beer. The objective of the current study was to localize the growth of Fusarium spp. within FHB-infected kernels by developing an improved method and to associate fungal growth with the production of DON during malting. FHB-infected barley, wheat, rye, and triticale grains that exhibited large increases in the amount of Fusarium Tri5 DNA and trichothecene mycotoxins following malting were screened for hyphal localization. The growth of fungal hyphae associated with grain and malt was imaged by scanning electron microscopy and confocal laser-scanning microscopy assisted with WGA-Alexa Fluor 488 staining, respectively. In barley, hyphae were present on or within the husk, vascular bundle, and pericarp cavities. Following malting, vast hyphal growth was observed not only in these regions but also in the aleurone layer, endosperm, and embryo. Extensive fungal growth was also observed following malting of wheat, rye, and triticale. However, these grains already had an extensive internal presence of Fusarium hyphae in the unmalted grain, thus representing an enhanced chance of fungal expansion during the malting.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Method for fast staining and obtaining high-magnification and high-resolution cell images of Nicotiana benthamiana

As tools of plant molecular biology, fluorescence microscopy and Nicotiana benthamiana have been used frequently to study the structure and function of plant cells. However, it is difficult to obtain ideal micrographs; for example, the images are typically unclear, the inner cell structure cannot be observed under a high-power lens by fluorescence microscopy, etc. Here, we describe a method for observing the cell structure of N. benthamiana. This method significantly improves imaging by fluorescence microscopy and allows clear images to be obtained under a high-power lens. This method is easy to perform with good stability, and the stomatal structure, nucleus, nucleolus, chloroplast and other organelles in N. benthamiana cells as well as protein localizations and the locations of protein-protein interactions have been observed clearly. Furthermore, compared with traditional methods, fluorescent dye more efficiently dyes cells with this method. The applicability of this method was verified by performing confocal scanning laser microscopy (CSLM), and CSLM imaging was greatly improved. Thus, our results provided a method to visualize the subcellular structures of live cells in the leaves of N. benthamiana by greatly improving imaging under a fluorescence microscope and provided new insights and references for the study of cell structures and functions in other plants.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00931-5.

From rhizoids to roots? Experimental evidence of mutualism between liverworts and ascomycete fungi

Background and Aims

The rhizoids of leafy liverworts (Jungermanniales, Marchantiophyta) are commonly colonized by the ascomycete fungus Pezoloma ericae. These associations are hypothesized to be functionally analogous to the ericoid mycorrhizas (ErMs) formed by P. ericae with the roots of Ericaceae plants in terms of bi-directional phosphorus for carbon exchange; however, this remains unproven. Here, we test whether associations between the leafy liverwort Cephalozia bicuspidata and P. ericae are mutualistic.

Methods

We measured movement of phosphorus and carbon between C. bicuspidata and P. ericae using [33P]orthophosphate and 14CO2 isotope tracers in monoxenic cultures. We also measured leafy liverwort growth, with and without P. ericae.

Key Results

We present the first demonstration of nutritionally mutualistic symbiosis between a non-vascular plant and an ErM-forming fungus, showing transfer of fungal-acquired P to the liverwort and of liverwort-fixed C to the fungus alongside increased growth in fungus-colonized liverworts.

Conclusions

Thus, this ascomycete-liverwort symbiosis can now be described as mycorrhiza-like, providing further insights into ericoid mycorrhizal evolution and adding Ascomycota fungi to mycorrhizal fungal groups engaging in mutualisms with plants across the land plant phylogeny. As P. ericae also colonizes the rhizoids of Schistochilaceae liverworts, which originated in the Triassic and are sister to all other jungermannialean liverworts associated with fungi, our findings point toward an early origin of ascomycete-liverwort symbioses, possibly pre-dating their evolution in the Ericales by some 150 million years.

Bioactivities by a crude extract from the Greenlandic Pseudomonas sp. In5 involves the nonribosomal peptides, nunamycin and nunapeptin

Background. Bioactive microbial metabolites provide a successful source of novel compounds with pharmaceutical potentials. The bacterium Pseudomonas sp. In5 is a biocontrol strain isolated from a plant disease suppressive soil in Greenland, which produces two antimicrobial nonribosomal peptides (NRPs), nunapeptin and nunamycin. Methods. In this study, we used in vitro antimicrobial and anticancer bioassays to evaluate the potential bioactivities of both a crude extract derived from Pseudomonas sp. In5 and NRPs purified from the crude extract. Results. We verified that the crude extract derived from Pseudomonas sp. In5 showed suppressive activity against the basidiomycete Rhizoctonia solani by inducing a mitochondrial stress-response. Furthermore, we confirmed suppressive activity against the oomycete Pythium aphanidermatum by the Pseudomonas sp. In5 crude extract, and that the purified nunamycin and nunapeptin displayed distinct antimicrobial activities. In addition to the antimicrobial activity, we found that treatment of the cancer cell lines, Jurkat T-cells, Granta cells, and melanoma cells, with the Pseudomonas sp. In5 crude extract increased staining with the apoptotic marker Annexin V while no staining of healthy normal cells, i.e., naïve or activated CD4 T-cells, was observed. Treatment with either of the NRPs alone did not increase Annexin V staining of the Jurkat T-cells, despite individually showing robust antimicrobial activity, whereas an anticancer activity was detected when nunamycin and nunapeptin were used in combination. Discussion. Our results suggest that the bioactivity of a crude extract derived from Pseudomonas sp. In5 involves the presence of both nunamycin and nunapeptin and highlight the possibility of synergy between multiple microbial metabolites.

Never say dye: new roles for an old fluorochrome

Recent years have seen a remarkable increase in the number of publications dealing with the application of epifluorescence microscopy in cell biology. This can be widely attributed to the development of state-of-the-art image processing programs, as well as the development of new reagents/probes, which allow the labeling of most cell structures, organelles and metabolites with high specificity. However, the use of a specific fluorescent dye, 3,3'-dihexyloxacarbocyanine iodide (DiOC₆), has been recently revisited and several new application potentials have emerged. The goal of this mini-review is to provide an up-to-date overview of the multiple roles of this multifaceted probe.

Sebacinales are associates of the leafy liverwort Lophozia excisa in the southern maritime Antarctic

The leafy liverwort Lophozia excisa, which is colonised by basidiomycete fungi in other biomes and which evidence suggests may be colonised by mycorrhizal fungi in Antarctica, was sampled from Léonie Island in the southern maritime Antarctic (67 degrees 36' S, 68 degrees 21' W). Microscopic examination of plants indicated that fungal hyphae colonised 78% of the rhizoids of the liverwort, apparently by entering the tips of rhizoids prior to growing into their bases, where they formed hyphal coils. Extensive colonisation of stem medullary cells by hyphae was also observed. DNA was extracted from surface-sterilised liverwort tissues and sequenced following nested PCR, using the primer set ITS1F/TW14, followed by a second round of amplification using the ITSSeb3/TW13 primer set. Neighbour-joining analyses showed that the sequences obtained nested in Sebacinales clade B as a 100% supported sister group to Sebacinales sequences from the leafy liverworts Lophozia sudetica, L. incisa and Calypogeia muelleriana sampled from Europe. Direct PCR using the fungal specific primer set ITS1F/ITS4 similarly identified fungi belonging to Sebacinales clade B as the principal colonists of L. excisa tissues. These observations indicate the presence of a second mycothallus in Antarctica and support the previous suggestion that the Sebacinales has a wide geographical distribution.

Conservation of cytoplasmic organization in the cystidia of Suillus species

Cystidia of Suillus americanus and S. granulatus (Boletales) were examined cytochemically and ultrastructurally with cells prepared by freeze substitution. We present the first study showing ultrastructural details and cytological functions of the cystidium to be conserved in two closely related species. The results are presented for inclusion in the AFTOL Structural and Biochemical Database <http://aftol.umn.edu> to aid in the application of morphological characters to phylogenetic studies. The cystidia of these Suillus species appear to be united by a series of conserved characters, including specialized secretion mechanisms, smooth tubular endoplasmic reticulum and abundant free ribosomes. The conservation of these subcellular traits among members of this genus suggests that ultrastructural details of cystidia may provide a suite of phylogenetically informative characters. Inclusion of such characters in phylogenetic analyses might resolve or provide support for monophyletic groups at the level of family or genus.

Two alternative recessive quantitative trait loci influence resistance to spring black stem and leaf spot in Medicago truncatula

BACKGROUND

Knowledge of the genetic basis of plant resistance to necrotrophic pathogens is incomplete and has been characterised in relatively few pathosystems. In this study, the cytology and genetics of resistance to spring black stem and leaf spot caused by Phoma medicaginis, an economically important necrotrophic pathogen of Medicago spp., was examined in the model legume M. truncatula.

RESULTS

Macroscopically, the resistant response of accession SA27063 was characterised by small, hypersensitive-like spots following inoculation while the susceptible interaction with accessions A17 and SA3054 showed necrotic lesions and spreading chlorosis. No unique cytological differences were observed during early infection (<48 h) between the resistant and susceptible genotypes, except pathogen growth was restricted to one or a few host cells in SA27063. In both interactions reactive oxygen intermediates and phenolic compounds were produced, and cell death occurred. Two F2 populations segregating for resistance to spring black stem and leaf spot were established between SA27063 and the two susceptible accessions, A17 and SA3054. The cross between SA27063 and A17 represented a wider cross than between SA27063 and SA3054, as evidenced by higher genetic polymorphism, reduced fertility and aberrant phenotypes of F2 progeny. In the SA27063 x A17 F2 population a highly significant quantitative trait locus (QTL, LOD = 7.37; P < 0.00001) named resistance to the necrotroph Phoma medicaginis one (rnpm1) genetically mapped to the top arm of linkage group 4 (LG4). rnpm1 explained 33.6% of the phenotypic variance in the population's response to infection depicted on a 1-5 scale and was tightly linked to marker AW256637. A second highly significant QTL (LOD = 6.77; P < 0.00001), rnpm2, was located on the lower arm of LG8 in the SA27063 x SA3054 map. rnpm2 explained 29.6% of the phenotypic variance and was fine mapped to a 0.8 cM interval between markers h2_16a6a and h2_21h11d. rnpm1 is tightly linked to a cluster of Toll/Interleukin1 receptor-nucleotide binding site-leucine-rich repeat (TIR-NBS-LRR) genes and disease resistance protein-like genes, while no resistance gene analogues (RGAs) are apparent in the genomic sequence of the reference accession A17 at the rnpm2 locus.

CONCLUSION

The induction of defence responses and cell death in the susceptible interaction following infection by P. medicaginis suggested this pathogen is not negatively affected by these responses and may promote them. A QTL for resistance was revealed in each of two populations derived from crosses between a resistant accession and two different susceptible accessions. Both loci are recessive in nature, and the simplest explanation for the existence of two separate QTLs is the occurrence of host genotype-specific susceptibility loci that may interact with undetermined P. medicaginis virulence factors.

Altered stomatal dynamics in ascorbate oxidase over-expressing tobacco plants suggest a role for dehydroascorbate signalling

Control of stomatal aperture is of paramount importance for plant adaptation to the surrounding environment. Here, we report on several parameters related to stomatal dynamics and performance in transgenic tobacco plants (Nicotiana tabacum L., cv. Xanthi) over-expressing cucumber ascorbate oxidase (AO), a cell wall-localized enzyme of uncertain biological function that oxidizes ascorbic acid (AA) to monodehydroascorbic acid which dismutates yielding AA and dehydroascorbic acid (DHA). In comparison to WT plants, leaves of AO over-expressing plants exhibited reduced stomatal conductance (due to partial stomatal closure), higher water content, and reduced rates of water loss on detachment. Transgenic plants also exhibited elevated levels of hydrogen peroxide and a decline in hydrogen peroxide-scavenging enzyme activity. Leaf ABA content was also higher in AO over-expressing plants. Treatment of epidermal strips with either 1 mM DHA or 100 microM hydrogen peroxide resulted in rapid stomatal closure in WT plants, but not in AO-over-expressing plants. This suggests that signal perception and/or transduction associated with stomatal closure is altered by AO over-expression. These data support a specific role for cell wall-localized AA in the perception of environmental cues, and suggest that DHA acts as a regulator of stomatal dynamics.

Inoculation of cranberry (Vaccinium macrocarpon) with the ericoid mycorrhizal fungus Rhizoscyphus ericae increases nitrate influx

Despite the ubiquitous presence of ericoid mycorrhizal (ERM) fungi in cranberry (Vaccinium macrocarpon), no prior studies have examined the effect of ERM colonization on NO(3)(-) influx kinetics. Here, (15)NO(3)(-) influx was measured in nonmycorrhizal and mycorrhizal cranberry in hydroponics. Mycorrhizal cranberry were inoculated with the ERM fungus Rhizoscyphus (syn. Hymenoscyphus) ericae. (15)NO(3)(-) influx by R. ericae in solution culture was also measured. Rhizoscyphus ericae NO(3)(-) influx kinetics were linear when mycelium was exposed for 24 h to 3.8 mm NH(4)(+), and saturable when pretreated with 3.8 mm NO(3)(-), 50 microm NO(3)(-), or 50 microm NH(4)(+). Both low-N pretreatments induced greater NO(3)(-) influx than either of the high-N pretreatments. Nonmycorrhizal cranberry exhibited linear NO(3)(-) influx kinetics. By contrast, mycorrhizal cranberry had saturable NO(3)(-) influx kinetics, with c. eightfold greater NO(3)(-) influx than nonmycorrhizal cranberry at NO(3)(-) concentrations from 20 microm to 2 mm. There was no influence of pretreatments on cranberry NO(3)(-) influx kinetics, regardless of mycorrhizal status. Inoculation with R. ericae increased the capacity of cranberry to utilize NO(3)(-)-N. This finding is significant both for understanding the potential nutrient niche breadth of cranberry and for management of cultivated cranberry when irrigation water sources contain nitrate.

Isolation, cloning and expression analysis of EcPMA1, a putative plasma membrane H+ -ATPase transporter gene from the biotrophic pathogenic fungus Erysiphe cichoracearum

Little is known at the molecular level about the transporters involved in nutrient transfer in the plant/powdery mildew interaction. A PCR-based approach was used to identify and isolate a partial-length cDNA coding for an isoform of the plasma membrane H+ -ATPase (EcPMA1) in the biotrophic pathogenic fungus Erysiphe cichoracearum. Southern analysis suggests that EcPMA1 exists as a single-copy gene. Sequence analysis indicated a high similarity of EcPMA1 to other fungal H+ -ATPases. Expression of EcPMA1 increases in infected Arabidopsis leaves as the disease progresses, correlating with the growth of the pathogen.

Endophytic Xylaria (Xylariaceae) among liverworts and angiosperms: phylogenetics, distribution, and symbiosis

Nuclear ribosomal 18S and internal transcribed spacer (ITS) sequence data were used to identify endophytic fungi cultured from six species of liverworts collected in Jamaica and North Carolina. Comparisons with other published fungal sequences and phylogenetic analyses yielded the following conclusions: (1) the endophytes belong to the ascomycete families Xylariaceae, Hypocreaceae, and Ophiostomataceae, and (2) liverwort endophytes in the genus Xylaria are closely related to each other and to endophytes isolated from angiosperms in China, Puerto Rico, and Europe. Liverwort endophytes are expected to be foragers or endophytic specialists, although little is known about the role of these fungi in symbioses. Features that may indicate a mutualistic role for these endophytes are discussed.

Subterranean gametophytic axes in the primitive liverwort Haplomitrium harbour a unique type of endophytic association with aseptate fungi

•  Haplomitrium, a primitive liverwort taxon with only remote affinities to other liverwort groups, develops root-like subterranean axes harbouring fungal endophytes. Here we report on the fungal association in H. gibbsiae and H. ovalifolium, using light and electron microscopy. •  The epidermal cells of subterranean axes secrete abundant mucilage that harbours aseptate fungal hyphae. The fungus penetrates the epidermal cells and forms intracellular arbuscules invested by the host cytoplasm. Infection is restricted to epidermal cells in H. gibbsiae, whereas in H. ovalifolium the fungus also infects the cortical cells immediately adjacent, where it forms prominent swellings ('lumps'). In H. gibbsiae similar fungal swellings are formed in the epidermal cells along with arbuscules. In both species the lumps undergo cytoplasmic degeneration and collapse, showing a shorter lifespan than the arbuscules. •  The fungal infection in Haplomitrium presents affinities with symbiotic associations with glomeromycotean fungi in higher plants (arbuscular mycorrhizas) and thalloid liverworts. However, the pattern of fungal morphogenesis in Haplomitrium has no precedent in bryophytes nor in higher plants. •  Considering the Glomeromycota as the most ancient lineage of mycorrhizal fungi, and Haplomitrium as basal in land plant phylogenies, the association described here may be the most primitive land plant-fungal symbiosis documented to date.

Heterobasidiomycetes form symbiotic associations with hepatics: Jungermanniales have sebacinoid mycobionts while Aneura pinguis (Metzgeriales) is associated with a Tulasnella species

In order to evaluate substrate dependence of the symbiotic fungal associations in leafy liverworts (Jungermanniopsida), 28 species out of 12 families were investigated by transmission electron microscopy and molecular methods. Samples were obtained from the diverse substrates: from naked soil, from the forest floor on needle litter, from between peat moss, from rotten bark of standing trees, and from stumps and rotten wood. Associations with ascomycetes were found in most of the specimens independent from the substrate. Seven species sampled from soil were found to contain basidiomycete hyphae. Ultrastructure consistently showed dolipores with imperforate parenthesomes. Molecular phylogenetic studies revealed that three specimens belonging to the Jungermanniales were associated with members of Sebacinaceae, while Aneura pinguis (Metzgeriales) was associated with a Tulasnella species. These taxa are so far the only basidiomycetes known to be symbiotically associated with leafy liverworts. The probability that the associations with Sebacinaceae are evolutionary old, but the Tulasnella associations more derived is discussed. The sebacinoid mycobionts form a similar interaction type with the jungermannialian leafy liverworts as do the associated ascomycetes. The term 'jungermannioid mycorrhiza' is proposed for this distinctive symbiotic interaction type.

Biology of mycorrhizal associations of epacrids (Ericaceae)

Epacrids, a group of southern hemisphere plants formerly considered members of the separate family Epacridaceae, are in fact most closely allied to the Vaccinioid tribe (Ericaceae). Epacrids and other extant ericoid mycorrhiza-forming plants appear to have a monophyletic origin. In common with many Ericaceae they form ericoid mycorrhizas. ITS sequence data indicate that the fungi forming ericoid mycorrhizas with epacrids and other extant Ericaceae are broadly similar, belonging to a poorly defined group of ascomycetes with phylogenetic affinities to Helotiales. The basic development and structure of ericoid mycorrhizal infections in epacrids is similar to other Ericaceae. However, data are limited on the structure and physiology of both hair roots and ericoid mycorrhizas for all Ericaceae. Relatively little is known about the functional significance of ericoid mycorrhizas in epacrids in southern hemisphere habitats that are often poor in organic matter accumulation. However the abilities of fungal endophytes of epacrids to utilize organic N and P substrates equal those of endophytes from northern hemisphere heathland plant hosts. Investigations using ¹⁵ N/¹³ C-labelled organic N substrates suggest that mycorrhizal endophytes are important, at least, to the N nutrition of their epacrid hosts in some habitats. Contents Summary 305 I. Epacrid plant hosts 306 II. Evolution of ericoid mycorrhizas in epacrids 306 III. Epacrid hair roots and their mycorrhizal associations 307 IV. Seasonality and incidence of mycorrhizal infection 310 V. Structure and development of mycorrhizal associations 311 VI. Nature of the mycorrhizal fungal endophytes 315 VII. Community and population biology of mycorrhizal endophytes 318 VIII. Functional aspects of mycorrhizas in epacrids 319 IX. Conclusions 322 Acknowledgements 322 References 322.

Isolation and characterization of broad-spectrum disease-resistant Arabidopsis mutants

To identify Arabidopsis mutants that constitutively express systemic acquired resistance (SAR), we constructed reporter lines expressing the firefly luciferase gene under the control of the SAR-inducible PR-1 promoter (PR-1/luc). After EMS mutagenesis of a well-characterized transgenic line, we screened 250,000 M(2) plants for constitutive expression of the reporter gene in vivo. From a mutant collection containing several hundred putative mutants, we concentrated on 16 mutants lacking spontaneous hypersensitive response (HR) cell death. We mapped 4 of these constitutive immunity (cim) mutants to chromosome arms. Constitutive expression of disease resistance was established by analyzing responses to virulent Peronospora parasitica and Pseudomonas syringae strains, by RNA blot analysis for endogenous marker genes, and by determination of salicylic acid levels in the mutants. The variety of the cim phenotypes allowed us to define distinct steps in both the canonical SAR signaling pathway and a separate pathway for resistance to Erysiphe cichoracearum, active in only a subset of the mutants.

Symbiotic fungal associations in 'lower' land plants

An analysis of the current state of knowledge of symbiotic fungal associations in 'lower' plants is provided. Three fungal phyla, the Zygomycota, Ascomycota and Basidiomycota, are involved in forming these associations, each producing a distinctive suite of structural features in well-defined groups of 'lower' plants. Among the 'lower' plants only mosses and Equisetum appear to lack one or other of these types of association. The salient features of the symbioses produced by each fungal group are described and the relationships between these associations and those formed by the same or related fungi in 'higher' plants are discussed. Particular consideration is given to the question of the extent to which root fungus associations in 'lower' plants are analogous to 'mycorrhizas' of 'higher' plants and the need for analysis of the functional attributes of these symbioses is stressed. Zygomycetous fungi colonize a wide range of extant lower land plants (hornworts, many hepatics, lycopods, Ophioglossales, Psilotales and Gleicheniaceae), where they often produce structures analogous to those seen in the vesicular-arbuscular (VA) mycorrhizas of higher plants, which are formed by members of the order Glomales. A preponderance of associations of this kind is in accordance with palaeohbotanical and molecular evidence indicating that glomalean fungi produced the archetypal symbioses with the first plants to emerge on to land. It is shown, probably for the first time, that glomalean fungi forming typical VA mycorrhiza with a higher plant (Plantago lanceolata) can colonize a thalloid liverwort (Pellia epiphylla), producing arbuscules and vesicles in the hepatic. The extent to which these associations, which are structurally analogous to mycorrhizas, have similar functions remains to be evaluated. Ascomycetous associations are found in a relatively small number of families of leafy liverworts. The structural features of the fungal colonization of rhizoids and underground axes of these plants are similar to those seen in mycorrhizal associations of ericaceous plants like Vaccinium. Cross inoculation experiments have confirmed that a typical mycorrhizal endophyte of ericaceous plants, Hymenoscyphus ericae, will form associations in liverworts which are structurally identical to those seen in nature. Again, the functional significance of these associations remains to be examined. Some members of the Jungermanniales and Metzgeriales form associations with basidiomycetous fungi. These produce intracellular coils of hyphae, which are similar to the pelotons seen in orchid mycorrhizas, which also involve basidiomycetes. The fungal associates of the autotrophic Aneura and of its heterotrophic relative Cryptothallus mirabilis have been isolated. In the latter case it has been shown that the fungal symbiont is an ectomycorrhizal associate of Betula, suggesting that the apparently obligate nature of the association between the hepatic and Betula in nature is based upon requirement for this particular heterotroph.

Comparison of Erysiphe cichoracearum and E. cruciferarum and a survey of 360 Arabidopsis thaliana accessions for resistance to these two powdery mildew pathogens

In previous work, UEA1 and UCSC1, two geographically distinct, powdery mildew isolates, were recognized for their ability to infect Arabidopsis thaliana. We have clarified the identity of these isolates by determining their host ranges, reexamining their morphology, and comparing their DNA sequences for the 5.8S ribosomal RNA and two flanking internal transcribed spacer sequences. These experiments confirm that UEA1 is a member of Erysiphe cruciferarum and that UCSC1 belongs to E. cichoracearum. Interactions of the two Erysiphe isolates with 360 A. thaliana accessions were examined to provide a comprehensive profile of naturally occurring powdery mildew resistance in this weedy species. The majority of A. thaliana accessions (213) were susceptible to both isolates. Among the accessions exhibiting some degree of resistance, most (84) responded differentially to UEA1 and UCSC1 and the remainder were resistant to both isolates. Notably, resistance to UCSC1 cosegregated with RPW7, a locus previously demonstrated to confer resistance to UEA1 in Ms-0 x Landsberg (erecta) crosses. With this large collection of resistant accessions, questions about species specificity, genetic diversity and the evolution of resistance to powdery mildews can be addressed.

DiOC6(3): a useful dye for staining the endoplasmic reticulum

The present review discusses the fluorescent organelle probe, DiOC6(3), with reference to its structure, chemistry, availability, spectral properties, labeling procedures, vital staining characteristics, and major applications in cellular and molecular biology. The specificity of dye for endoplasmic reticulum is summarized. We examine the simplicity and advantages of the fluorescent dye system for evaluating structure and function of endoplasmic reticulum. Other significant uses of the dye are also discussed.

The fluorescent dye 3, 3' dihexyloxacarbocyanine iodide selectively stains the midpiece and apical region of the heads of murid rodent spermatozoa

Fluorescence microscopy of caudal epididymal spermatozoa stained with 3, 3' dihexyloxacarbocyanine iodide (DiOC6(3)) showed intense fluorescence along the concave surface of the apical hook of spermatozoa of Rattus species and along the upper concave margin of the sperm head in Mus musculus. In the spermatozoa of Hydromys chrysogaster, Melomys cervinipes, and Pseudomys australis, the two ventral processes also fluoresced brightly. In P. australis, fluorescence in the apical hook of sperm heads was largely localized to its upper and lower surfaces. The sperm of N. alexis did not show consistent positive fluorescence. The localization of fluorescence in these spermatozoa after staining with DiOC6(3) was mainly restricted to regions where a large accumulation of perinuclear theca material lies beneath the plasmalemma. The reason for this remains to be determined, but DiOC6(3) may be useful for quickly demonstrating areas of abundant perinuclear thecal material in sperm heads of eutherian mammals by light microscopy.