Sporogenous Cells Research Articles

Nuclear membranes and inclusions in overwintering sporogenous cells of Scotch pine

The sporogenous nuclei of the Scotch pine (Pinus sylvestris L.) produce membraneous structures, the type and the number of which vary during the course of the yearly cycle. The nuclear membranes develop both evaginations and invaginations. Part of the structures seen inside the nuclei seem to originate separate from the nuclear membranes. The intranuclear vesicles and vacuoles are either multimembraneous or surrounded by a single or a double membrane. Some nuclei contain small crystals. Fibrous areas, supposedly representing extrachromatin matrix, occur frequently in nuclei staying at prolonged interphases.

The GhACS1 gene encodes an acyl‐CoA synthetase which is essential for normal microsporogenesis in early anther development of cotton

Microsporogenesis, associated with the functional expression of many genes, is a highly programmed and regulated process in flowering plants. To elucidate the roles of genes during anther development, two anther-specific cDNAs (designated GhACS1 and GhACS2) encoding acyl-CoA synthetases (ACSs) were isolated from a cotton (Gossypium hirsutum) flower cDNA library. Subsequently, the corresponding GhACS1 gene was isolated from a cotton genomic DNA library. Real-time quantitative RT-PCR and northern blot analyses revealed that GhACS1 transcripts were predominantly accumulated in the developing anthers of cotton. The specificity of GhACS1 expression in primary sporogenous cells (PSCs), pollen mother cells (PMCs), microspores, and tapetal cells was demonstrated by in situ hybridization as well as histochemical assay of GUS expression controlled under the GhACS1 promoter. High levels of GhACS1 activity are crucial for fatty acid metabolism in PSCs, PMCs, microspores and particularly tapetal cells. Reduction of ACS enzymatic activity by suppressing GhACS1 expression severely affected the tapetal cells and consequently blocked normal microsporogenesis in early anther development. Aberrant and defective microspores were generated in the transgenic anthers. As a result, the transgenic plants failed to produce functional pollen grains and were male-sterile, suggesting that the GhACS1 gene is required for normal microsporogenesis in early anther development of cotton.

Genetic and histological characterization of a novel recessive genic male sterile line of Brassica napus derived from a cross with Capsella bursa-pastoris

In a previously made cross Brassica napus cv. Oro (2n = 38) × Capsella bursa-pastoris (2n = 4x = 32), one F1 hybrid with 2n = 38 was totally male sterile. The hybrid contained no complete chromosomes from C. bursa-pastoris, but some specific AFLP (amplified fragment length polymorphism) bands of C. bursa-pastoris were detected. The hybrid was morphologically quite similar to ‘Oro’ except for smaller flowers with rudimentary stamens but normal pistils, and showed good seed-set after pollination by ‘Oro’ and other B. napus cultivars. The fertility segregation ratios (3:1, 1:1) in its progenies indicated that the male sterility was controlled by a single recessive gene. In the pollen mother cells of the male sterile hybrid, chromosome pairing and segregation were normal. Histological sectioning of its anthers showed that the tapetum was multiple layers and was hypertrophic from the stage of sporogenic cells, and that the tetrads were compressed by the vacuolated and disaggregated tapetum and no mature pollen grains were formed in anther sacs, thus resulting in male sterility. The possible mechanisms for the production of the male sterile hybrid and its potential in breeding are discussed.

Sporoderm development in Trevesia burckii (Araliaceae). I. Tetrad period: Further evidence for the participation of self-assembly processes

The developmental events in the periplasmic space and cytoplasm of microspores, and in the tapetum of Trevesia burckii during the tetrad period have been traced in detail during microspore ontogeny from the sporogenous cell stage to the late tetrad stage and the initiation of the foot layer. The data obtained provide support to two of our previously proposed hypotheses: (1) the glycocalyx (scaffolding primexine matrix) is a colloidal system; (2) the involvement of processes of self-assembly of a number of colloidal micellar systems to the exine development. The main structures of the reticulate ectexine up to the establishment of the foot layer are columellae and tectum which evidently form on a base of spherical and cylindrical transitive micelle mesophases after sporopollenin accumulation. The importance of the callose envelope surrounding microspores for exine development is discussed in the light of recent findings. Two possible pathways of pattern determination are possible. One suggests the role of the plasma membrane in pattern imprinting and the corresponding necessity of the transfer of 2-D information to 3-D. Our current supposition is that the other, self-assembly physical phenomena, cellular tensegrity, also participate in the process of the establishment of a wide-spread reticulate exine pattern which appears as the result of an interplay of the microspore cytoskeletal prestress and the resistance from the ECM (exocellular matrix = glycocalyx) adhesive sites. More and more information is appearing that provides evidence for the importance of mechanical forces and physico-chemical regularities in the living world.

The novel Cladosporium fulvum lysin motif effector Ecp6 is a virulence factor with orthologues in other fungal species

During tomato leaf colonization, the biotrophic fungus Cladosporium fulvum secretes several effector proteins into the apoplast. Eight effectors have previously been characterized and show no significant homology to each other or to other fungal genes. To discover novel C. fulvum effectors that might play a role in virulence, we utilized two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) to visualize proteins secreted during C. fulvum-tomato interactions. Three novel C. fulvum proteins were identified: CfPhiA, Ecp6 and Ecp7. CfPhiA shows homology to proteins found on fungal sporogenous cells called phialides. Ecp6 contains lysin motifs (LysM domains) that are recognized as carbohydrate-binding modules. Ecp7 encodes a small, cysteine-rich protein with no homology to known proteins. Heterologous expression of Ecp6 significantly increased the virulence of the vascular pathogen Fusarium oxysporum on tomato. Furthermore, by RNA interference (RNAi)-mediated gene silencing we demonstrate that Ecp6 is instrumental for C. fulvum virulence on tomato. Hardly any allelic variation was observed in the Ecp6 coding region of a worldwide collection of C. fulvum strains. Although none of the C. fulvum effectors identified so far have obvious orthologues in other organisms, conserved Ecp6 orthologues were identified in various fungal species. Homology-based modelling suggests that the LysM domains of C. fulvum Ecp6 may be involved in chitin binding.

Cytological Observation of Microsporogenesis in Male-Sterile Lines of Chinese Pink ( Dianthus chinensis L.)

This study addressed the differences in microsporogenesis between male sterile and fertile lines of Chinese pink. The microsporogenesis processes of male sterile and fertile lines were histologically examined in squashed pollen grains and in paraffin embedded sections. A stable male-sterile line (H-37B) was obtained following six generations of inbreeding in a self-fertile line, followed by two generations of backcrossing. In the corresponding fertile line, development of the mature pollen grains was followed through the initiation of the sporogenous cell, microsporocyte formation, and the tetrad developmental period. In the male-sterile line, abortion of the developing pollen grains was observed to take place at various stages, namely, sporogenous cell growth, mother cell meiosis, and tetrad transformation to the uninuclear state. The pollen grains of the fertile line were spheroid, turgid, and viable. By contrast, the male-sterile line produced pollen that was irregular in shape, empty, and nonviable. The abortion of the microspore in the male-sterile line appeared to relate to abnormal growth of the tapetum layer.

Formation of membrane‐bound inclusions and their associations with cytoplasmic channels in early prophase male meiocytes of Althaea rosea (L.) Cavan

To characterize the cytoplasmic structure reorganization during plant meiosis, the male meiocytes of Althaea rosea (L.) Cavan were examined under the combination of light and electron microscopy. Light microscopic observation of the toluidine blue-stained thick resin sections of young anthers revealed that the meiocytes of sporogenous cell stage were extremely voluminous and variable in shape and division plane. The cell walls (CWs) between some meiocytes were discontinuous at one or several site(s). These discontinuous portions varied between 0.2 and 3.0 microm in length. In addition, it was found that some meiocytes were able to produce protuberances that extended into another meiocyte. When transversally sectioned, the protuberance extending to another cell looked like a small cell lying in another cell. Transmission electron microscopy (TEM) showed that there were many long flat ER cisternae that were actively wrapping around a portion of cytoplasm in the male meiocytes at the sporogenous cell stage. During pre-meiosis interphase and early prophase I, a number of huge (0.5-1.0 microm diameter) spherical membrane-bound inclusions (MBIs) lined by single or double layer(s) of membrane were formed, each membrane actually representing one tightly appressed endoplasmic reticulum (ER) cisterna. The MBIs contained many granular, lamellar and fibrillar structures, and even small MBIs. Moreover, it was found that the MBIs could associate with the cytoplasmic channels (CCs) on CWs to release their contents into the cytoplasm of the opposite cell or directly extend from one cell to another through the CC. Taking all the data together, it is suggested that association of the MBIs and other organelles with CCs possibly functions in eliminating the non-identity of cytoplasm of the male meiocytes caused probably by the random asymmetric division observed at sporogenous cell phase, so as to ensure production of a large number of identical functional male gametes required for successful fertilization.

Male Sterile Lines of Zinnia elegans and Their Cytological Observations

In order to find out a new pathway for utilizing heterosis of Zinnia elegans and accelerate breeding process, the mechanism of anther development of a male sterile line was explored. Backcross, sibmating, selfing of fertile plants and testcross with inbred lines were analyzed and identified in the field, and cytology was observed. Recessive nucleus male sterile line AH209AB capable of being a maintainer was obtained by successive backcrosses with male sterile plants and fertile F1 plants as male parents. Cytological and anatomical studies indicated that: (1) The wall of normal anther was constituted of four layers of cells such as epidermis, powder chamber wall, middle level and tapetum cells. The process in meiosis of pollen mother cell in Zinnia elegans was normal and cytoplasm divided simultanously. Mature pollen grain was tricellular type. (2) The petal of male sterile plant degraded as a thread-like structure, the stamens were villiform in appearance and no pollens were formed. The result showed that the anther of male sterile plant no longer proceed to differentiate spore mother cell and the pollen sac after the formation of the tissue of sporogenous cells, there was no evident boundary between tapetum cell, middle lamella and inner wall of PMC, tapetal cells did not develop from the very beginning. So the abortion type was completely structural male sterility. The male sterile line belongs to non-sporange male sterile type and is of great use in F1 seeds production.

Embryology of the dioecious Australian endemic Lomandra longifolia (Lomandraceae)

Microsporogenesis, embryogeny and endosperm development of Lomandra longifolia Labill. are described in detail. The formation of the anther wall is the basic type composed of four cell layers, namely an epidermis, an endothecium, one middle layer and a tapetum. The tapetum layer has glandular, uninucleate cells. Successive cytokinesis follows meiosis, subsequently forming a tetrahedral tetrad of microspores. The ovule in each carpel is hemitropous, crassinucellate and bitegmic, with the micropyle formed by the inner integument. The archesporial cell divides periclinally to form the primary parietal and primary sporogenous cells. The sporogenous cell functions as the megaspore mother cell, whereas the parietal cell divides to give rise to two parietal layers. The mature megagametophyte, which has enlarged synergids and antipodals, is of the Polygonum type, with the normal complement of seven cells and eight nuclei. Nucellar tissue in the mature ovule consists of enlarged dermal cells and irregular subdermal cells surrounding a central strand of markedly smaller cells. Endosperm development is of the nuclear type. Embryo development is of the Graminad type, characterised by oblique zygotic and early pro-embryonic divisions.

Ultrastructure of teliospores and promycelium and basidiospore formation in the two-spored form of Gymnoconia nitens, one of the causes of orange rust of Rubus

Gymnoconia nitens (Schwein.) Kern & H. W. Thurston consists of two forms that cause orange rust of Rubus . The teliospores of both of these forms are morphologically identical to aeciospores, but upon germination form promycelia that give rise to either two or four basidiospores. In this study, we examined the teliospores and the sequence of events leading to basidiospore development in the two-spored form of G. nitens. The teliospores of this species are formed in chains from uninucleate sporogenous cells that line the base of each sorus on infected Rubus argutus Link. (blackberry) leaves. Fluorescence microscopy revealed that approximately 90% of the mature teliospores were uninucleate. During germination, the teliospore nucleus migrated into the developing promycelium and underwent a single mitotic division. A transverse septum formed between the two daughter nuclei creating two uninucleate cells. A tapered sterigma arose from each cell and gave rise to a basidiospore. These findings indicate that the basidiospores of the two-spored form of G. nitens were formed in an asexual fashion.

Differential gene expression in Arabidopsis wild‐type and mutant anthers: insights into anther cell differentiation and regulatory networks

In flowering plants, the anther contains highly specialized reproductive and somatic cells that are required for male fertility. Genetic studies have uncovered several genes that are important for anther development. However, little information is available regarding most genes active during anther development, including possible relationships between these genes and genetically defined regulators. In Arabidopsis, two previously isolated male-sterile mutants display dramatically altered anther cell differentiation patterns. The sporocyteless (spl)/nozzle (nzz) mutant is defective in the differentiation of primary sporogenous cells into microsporocytes, and does not properly form the anther wall. The excess microsporocytes1 (ems1)/extrasporogenous cells (exs) mutants produce excess microsporocytes at the expense of the tapetum. To gain additional insights into microsporocyte and tapetum differentiation and to uncover potential genetic interactions, expression profiles were compared between wild-type anthers (stage 4-6) and those of the spl or ems1 mutants. A total of 1954 genes were found to be differentially expressed in the ems1 and/or spl anthers, and these were grouped into 14 co-expression clusters. The presence of genes with known and predicted functions in specific clusters suggests potential functions for other genes in the same cluster. To obtain clues about possible co-regulation within co-expression clusters, we searched for shared cis-regulatory motifs in putative promoter regions. Our analyses were combined with data from previous studies to develop a model of the anther gene regulatory network. This model includes hypotheses that can be tested experimentally to gain further understanding of the mechanisms controlling anther development.

Analysis of Differentially Expressed Genes in Genic Male Sterility Cotton ( Gossypium hirsutum L.) Using cDNA-AFLP

cDNA amplified fragment length polymorphism (cDNA-AFLP) analysis was used to investigate the differentially expressed genes between sterile and fertile plants of ms5ms6 double-recessive genic male sterility (GMS) two-type line cotton ( Gossypium hirsutum L.) at different stages, i.e., sporogenous cell stage, pollen mother cell (PMC) stage, and pollen grain stage. Seventeen differentially expressed fragments were identified. Functional analysis indicated that their corresponding genes may participate in the processes of signal transduction, transcription, energy metabolism, and plant cell wall development. Northern blot demonstrated the credibility of the result of cDNA-AFLP. A sterility restorer factor-like gene, which only expressed in fertile anther and was notably homologous to T cytoplasm male sterility restorer factor 2 of maize ( Zea mays L.), was identified in this research.

Metabolism of reactive oxygen species in cotton cytoplasmic male sterility and its restoration

To elucidate reactive oxygen species (ROS) metabolism of cotton cytoplasmic male sterility and the effects of restorer gene on the metabolism of ROS, the metabolism changes in the production and scavenging of ROS and gene expression related to ROS-scavenging enzymes were investigated in the anther mitochondria of CMS line, maintainer line and hybrid F(1). During the abortion preliminary stage (sporogenous cell division stage), anthers of CMS line had a little higher superoxide (O(2)(-)) production rate and hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) contents than those of maintainer or hybrid F(1. )Simultaneously, a little higher ROS contents might serve as a signal to increase the activity of superoxide dismutase (SOD) in anthers of CMS line to reduce the ROS damage to the anther development. But at the abortion peak (pollen mother cell meiosis stage), anthers of CMS line had extraordinarily higher ROS contents and lower ROS-scavenging enzymic activities compared with the hybrid F(1), during which the ROS contents and ROS-scavenging enzymic activities in hybrid F(1) were approximate to those of maintainer line. The expression of Mn-sod and apx mRNA in anther of CMS line was obviously inhibited when ROS produced with a great deal during anther abortion, however the gene expression in hybrid F(1) kept normal with the maintainer. Excessive accumulation of O(2)(*-) , H(2)O(2 )and MDA, significant reduction of ROS-scavenging enzymic activities and lower gene expression level of ROS-scavenging enzyme were coinstantaneous with male cells death in anthers of CMS line. But when the restorer gene was transferred into CMS line, excessive production of ROS could be eliminated in the anthers of hybrid F(1). The restorer gene likely plays an important role in keeping the dynamic balance between the production and elimination of ROS.

Metabolism of Reactive Oxygen Species in the Cytoplasmic Male-Sterile Cotton Anther

Reactive oxygen species (ROS) in plant cell, including superoxide (O 2), hydrogen peroxide (H 2O 2), and malondialdehyde (MDA), are thought to be important inducible factors of cell apoptosis if excessively accumulated in cells. To elucidate the metabolic mechanism of ROS production and scavenging in anthers of the cytoplasmic male-sterile (CMS) cotton. CMS line, maintainer, and hybrid F 1 anthers, were employed for studying the relationship between CMS and metabolism of ROS, by comparing ROS changes in the sterile and fertile anthers at different developmental stages. The results showed that during the abortion preliminary stage (sporogenous cell division stage), anthers of CMS line had higher contents of O 2, H 2O 2, and MDA than those of maintainer or hybrid F 1. Simultaneously, the higher activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in scavenging ROS were measured in the anthers of the CMS line, indicating that an increase of ROS in anthers of abortion preliminary stage had an inducible effect on the antioxidant enzymes. But during the abortion peak of CMS anther (pollen mother cell meiosis stage), on the one hand, contents of O 2. H 2O 2, and MDA were extraordinarily high in CMS anthers, on the other hand, the activities of SOD, CAT, and POD were excessively low, which disrupted the balance between the production and elimination of ROS and led to pollen mother cells apoptosis at this stage. In the following two stages (uninucleate microspore stage and mature pollen stage), the contents of O 2 and H 2O 2 in the aborted anthers were approximated to contents in the fertile anthers of the maintainer and hybrid F 1. However, MDA contents were continuously raised and enzymic activities of SOD, CAT, and POD were consistently decreased in sterile anthers, which indicated that ROS still had harmful effects on the anthers after the apoptosis of the male cells. Excessive accumulation of O 2, H 2O 2, and MDA and significant reduction of ROS scavenging-enzyme activities were coinstantaneous with male cells apoptosis in the anthers of the cotton CMS line. But when the restorer gene was transferred into the CMS line, excessive production of ROS could be eliminated in the anthers of hybrid F 1.

Cytological investigation on microsporogenesis of male sterility of pepper

Cytological investigation on microsporogenesis of male sterility of pepper were studied, the results were as following: Abortion was found from multiplication stage of sporogenous cells.Sporogenous cells were vacuolated, misshapen, stretched-out and the clearance between cells was enlarged. Tapetum cells were elongated, vacuolated or tapetum was made up of multilayer cells or discomposed tardily. The structure of powder chamber was abnormal and replaced by indifferentiated cells full of thin cytoplasm. Cell layers of powder chamber wall and middle-level were increased, tapetum cells were hypertrophied and sporogenous cells or microspore mother cells were disaggregated. Quartered microspore couldn’t be released because the callose wall of microspores couldn’t decompose. Cytoplasm of monocytic microspore were decompounded.

Regulation of Arabidopsis tapetum development and function by DYSFUNCTIONAL TAPETUM1 (DYT1) encoding a putative bHLH transcription factor

In flowering plants, male fertility depends on proper cell differentiation in the anther. However, relatively little is known about the genes that regulate anther cell differentiation and function. Here, we report the analysis of a new Arabidopsis male sterile mutant, dysfunctional tapetum1 (dyt1). The dyt1 mutant exhibits abnormal anther morphology beginning at anther stage 4, with tapetal cells that have excess and/or enlarged vacuoles and lack the densely stained cytoplasm typical of normal tapetal cells. The mutant meiocytes are able to complete meiosis I, but they do not have a thick callose wall; they often fail to complete meiotic cytokinesis and eventually collapse. DYT1 encodes a putative bHLH transcription factor and is strongly expressed in the tapetum from late anther stage 5 to early stage 6, and at a lower level in meiocytes. In addition, the level of DYT1 mRNA is reduced in the sporocyteless/nozzle (spl/nzz) and excess microsporocytes1/extra sporogenous cell (ems1/exs) mutants; together with the mutant phenotypes, this suggests that DYT1 acts downstream of SPL/NZZ and EMS1/EXS. RT-PCR results showed that the expression levels of many tapetum-preferential genes are reduced significantly in the dyt1 mutant, indicating that DYT1 is important for the expression of tapetum genes. Our results support the hypothesis that DYT1 is a crucial component of a genetic network that controls anther development and function.

Expression of ASK1-like genes in arrested stamens of female Silene latifolia plants

Silene latifolia is a dioecious plant in which sex is determined by heteromorphic sex chromosomes. In female plants, stamen development is arrested before microspore mother cells are formed. In this study, we isolated four cDNAs (SlSKP1-1 to 4) encoding ASK1-like protein as expression markers to reveal when expression levels are reduced in arrested stamens of female flowers. Expression patterns of the SlSKP1 genes were analyzed by in-situ hybridization. We use the flower development classification of Grant et al. (in Plant J 6:471-480, 1994). SlSKP1 genes were highly expressed in primary parietal cells and primary sporogenous cells that develop into microspore mother cells in male flowers. Expression levels started to be reduced in the external stamens of the female flowers when stamen development was arrested at stage 7. Although microspore mother cells could not be developed in female flowers and SlSKP1 expression may be unnecessary in arrested stamens, SlSKP1 genes were still expressed in sporogenous cells of degenerated stamens at stage 8. Parietal cells stopped differentiating earlier than sporogenous cells in arrested stamens. These results suggest that not all types of cell are arrested simultaneously at a particular stage of stamen development during stamen suppression of S. latifolia.

Cytoplasmic channels and their association with plastids in male meiocytes of tobacco, onion and lily

The ultrastructures of male meiocytes in tobacco, onion and lily were studied to elucidate the interaction between cytoplasmic channels (CCs) and plastids. Before meiosis, the male sporogenous cells had identically thickened cell walls (CWs) traversed by typical plasmodesmata (PDs). After entering meiosis, their CWs became uneven in thickness and 80-500nm aperture CCs were formed. Simultaneously, plastids or plastid-like bodies (PLBs) differing in size and morphology assembled at one or both ends of the CCs. These plastids and PLBs commonly orientated their sharper ends to face the CCs and were co-orientated on the axial line crossing the CC. Such pairs of plastids were often interconnected through the CC by thin (50-100nm) threads emanating from their membranes. Sometimes, plastids or PLBs extended directly from one side of a CW to the other, forming a bridge via the CC. In some cases, several plastids formed bridges between cells via one common CC. This is the first report that clearly demonstrates an intercellular continuum of, or communication between, plastids in male plant meiocytes.

Bibulocystisgen. nov. (Uredinales) onDaviesia(Fabaceae) andAlbizia(Mimosaceae) in Australasia, with comments on the generaCystomycesandDicheiriniaand rust genera with teliospore cysts

The five known genera of Uredinales with hygroscopic teliospore cysts, Cystomyces, Kemkampella, Ravenelia, Spumula and Uromycladium, are discussed. Of these, the monotypic Cystomyces, type species C. costaricensis, is the only one with teliospores composed of a simple, monohyphal pedicel attached to cysts, which bear the fertile cells. A rust of Daviesia species in south-eastern Australia was thought originally to be an undescribed species of Cystomyces. Type material of C. costaricensis has been studied. Whereas Cystomyces has teliospores borne on percurrently proliferating sporogenous cells and three, dark-walled fertile cells with apical germ slits, the Duviesia rust has teliospores borne on sympodially proliferating sporogenous cells and four, palewalled fertile cells, each with an apical germ pore. Its teliospores show a complex arrangement of cysts and fertile cells, which is described and illustrated. These and other differences indicate that the Duviesia rust represents a previously unknown genus, described here as Bibulocystis gen. nov., type species B. pulcherrima var. pulcherrima. A single collection from the Central Tablelands of NSW with smaller, often irregular, teliospores is described as B. pulcherrima var. monticola. Only pycnia and telia are known for the two varieties. An emended description of the genus Cystosnyces is given. The full-cycled rust of Albizia from New Caledonia described as Dicheirinia viennotii is compared with original material of the type species of Dicheirinia, D. binata. Whilst Dicheirinia has teliospores with ornamented fertile cells borne on sterile cells, teliospores of the Albizia rust have smooth fertile cells borne on hygroscopic cysts. As its teliospores closely resemble those of the Australian Daviesia rusts, it is transferred as Bibulocystis viennotii. The characteristics and taxonomic position of the other 11 species currently placed in Dicheirinia are summarised briefly. Bibulocystis is the sixth rust genus with hygroscopic teliospore cysts and the fourth recorded in Australia, with Kernkampella, Ravenelia and Uromycladium.

Ultrastructural analysis of the behavior of the dimorphic fungus Microbotryum violaceum in fungus-induced anthers of female Silene latifolia flowers

The development of male organs is induced in female flowers of the dioecious plant Silene latifolia by infection with the fungus Microbotryum violaceum. Stamens in a healthy female flower grow only to stage 6, whereas those in an infected female flower develop to the mature stage (stage 12), at which the stamens are filled with fungal teliospores instead of pollen grains. To investigate these host-parasite interactions, young floral buds and fungus-induced anthers of infected female flowers were examined by electron microscopy following fixation by a high-pressure freezing method. Using this approach, we found that parasitic hyphae of this fungus contain several extracellular vesicles and have a consistent appearance up to stage 8. At that stage, parasitic hyphae are observed adjacent to dying sporogenous cells in the infected female anther. At stage 9, an increased number of dead and dying sporogenous cells is observed, among which the sporogenous hyphae of the fungus develop and form initial teliospores. Several types of electron-dense material are present in proximity to some fungi at this stage. The initial teliospores contain two types of vacuoles, and the fungus cell wall contains abundant carbohydrate, as revealed by silver protein staining. The sporogenous cell is probably sensitive to infection by the fungus, resulting in disruption. In addition, the fungus accelerates cell death in the anther and utilizes constituents of the dead host cell to form the mature teliospore.