Tomato POLLEN DEFICIENT 2 encodes a G-type lectin receptor kinase required for viable pollen grain formation.

Pollen development is a crucial biological process indispensable for seed set in flowering plants and for successful crop breeding. However, little is known about the molecular mechanisms regulating pollen development in crop species. This study reports a novel male-sterile tomato mutant, pollen deficient 2 (pod2), characterized by the production of non-viable pollen grains and resulting in the development of small parthenocarpic fruits. A combined strategy of mapping-by-sequencing and RNA interference-mediated gene silencing was used to prove that the pod2 phenotype is caused by the loss of Solanum lycopersicum G-type lectin receptor kinase II.9 (SlG-LecRK-II.9) activity. In situ hybridization of floral buds showed that POD2/SlG-LecRK-II.9 is specifically expressed in tapetal cells and microspores at the late tetrad stage. Accordingly, abnormalities in meiosis and tapetum programmed cell death in pod2 occurred during microsporogenesis, resulting in the formation of four dysfunctional microspores leading to an aberrant microgametogenesis process. RNA-seq analyses supported the existence of alterations at the final stage of microsporogenesis, since we found tomato deregulated genes whose counterparts in Arabidopsis are essential for the normal progression of male meiosis and cytokinesis. Collectively, our results revealed the essential role of POD2/SlG-LecRK-II.9 in regulating tomato pollen development.

Evolution and diversity of the angiosperm anther: trends in function and development.

KEY MESSAGE: Anther development and dehiscence is considered from an evolutionary perspective to identify drivers for differentiation, functional conservation and to identify key questions for future male reproduction research. Development of viable pollen and its timely release from the anther are essential for fertilisation of angiosperm flowers. The formation and subsequent dehiscence of the anther are under tight regulatory control, and these processes are remarkably conserved throughout the diverse families of the angiosperm clade. Anther development is a complex process, which requires timely formation and communication between the multiple somatic anther cell layers (the epidermis, endothecium, middle layer and tapetum) and the developing pollen. These layers go through regulated development and selective degeneration to facilitate the formation and ultimate release of the pollen grains. Insight into the evolution and divergence of anther development and dehiscence, especially between monocots and dicots, is driving greater understanding of the male reproductive process and increased, resilient crop yields. This review focuses on anther structure from an evolutionary perspective by highlighting their diversity across plant species. We summarise new findings that illustrate the complexities of anther development and evaluate how they challenge established models of anther form and function, and how they may help to deliver future sustainable crop yields.

Nymphaea colorata, another basal angiosperm species with bidirectional cytokinesis in microsporogenesis.

Comparing cellular features in microsporogenesis across taxa may yield important clues to evolution of meiosis in plants. We previously provided evidence that bidirectional cytokinesis occurs in M. denudata and suggested that the same may also occur in P. trimera based on a published report. Both M. denudata and P. trimera are basal angiosperm species that belong to the order of Magnoliales. For comparison, only unidirectional cytokinesis, either centripetal or centrifugal cytokinesis, has been found in microsporogenesis in eudicots and monocots. These observations raise the possibility that bidirectional cytokinesis is a common feature of microsporogenesis in basal angiosperms but not in eudicots and monocots. In this report, we provide evidence that bidirectional cytokinesis also occurs in another basal angiosperm species, Nymphaea colorata. The new findings, together with the previous findings, indicate that bidirectional cytokinesis is a prominent feature of microsporogenesis in at least some basal angiosperm species, and it occurs independently of cytokinesis types with respect to the timing of cytokinesis and tetrad configurations.

Cytological and genetic characterisation of dominant GMS line Shaan-GMS in Brassica napus L.

Genic male sterility (GMS) is an effective pollination control system applied in the hybrid breeding of Brassica napus L. Shaan-GMS is a spontaneous mutant of dominant GMS in B. napus. In this research, anther abortion in the homozygous two-type line 9A15AB derived from Shaan-GMS was characterised with the combined use of light microscopy and transmission electron microscopy. Results indicated that the most striking differences between the fertile and sterile plants occurred in the tapetum in the early microsporocyte stage. In sterile plants, the tapetal cells were irregularly arranged, multi-layered and occupied the growing space of microsporocytes. When entering into meiosis, the tapetum cells degraded and the cytoplasm fused. Some oval monolayer or bilayer membrane organelles existed in the tapetal cells in sterile anthers. Mitochondria in the tapetal cells were abnormal, and middle layer cells degraded early. Pollen mother cells of Shaan-GMS degenerated at the start of meiosis and ceased at the anaphase I stage, with no dyads or tetrads formed. The combined effects of the abnormal development of the tapetum, the middle layer cells and meiosis lead to male sterility in Shaan-GMS. Inheritance of male sterility of Shaan-GMS is controlled by a monogenically multiallelic locus with three different alleles (Ms, ms and Mf), with a relationship expressed as Mf > Ms and Ms > ms. The findings help lay the foundation for illustrating the mechanism of male sterility and the utilisation of Shaan-GMS in rapeseed.

Distribution of plastids and mitochondria during male gametophyte formation in Tinantia erecta (Jacq.) Fenzl.

During meiosis in microsporogenesis, autonomous cellular organelles, i.e., plastids and mitochondria, move and separate into daughter cells according to a specific pattern. This process called chondriokinesis is characteristic for a given plant species. The key criterion for classification of the chondriokinesis types was the arrangement of cell organelles during two meiosis phases: metaphase I and telophase I. The autonomous organelles participate in cytoplasmic inheritance; therefore, their precise distribution to daughter cells determines formation of identical viable microspores. In this study, the course of chondriokinesis during the development of the male gametophyte in Tinantia erecta was analyzed. The study was conducted using optical and transmission electron microscopes. During microsporogenesis in T. erecta, autonomous cell organelles moved in a manner defined as a neutral-equatorial type of chondriokinesis. Therefore, metaphase I plastids and mitochondria were evenly dispersed around the metaphase plate and formed an equatorial plate between the daughter nuclei in early telophase I. Changes in the ultrastructure of plastids and mitochondria during pollen microsporogenesis were also observed.

Low temperature-induced aberrations in male and female reproductive organ development cause flower abortion in chickpea.

Chickpea (Cicer arietinum L.) is susceptible to low temperature (LT) at reproductive stage. LT causes flower abortion and delays pod set in chickpea until terminal drought becomes an issue, thereby decreasing yield potential. In chickpea, flower and anther/pollen development as well as LT-induced abnormalities on anther and pollen development are described inadequately. In the present manuscript, we report flower development stages, anther development stages, and aberrations in male gamete formation in chickpea under LT. Flower length was linearly correlated to flower and anther stages and can be used to predict these stages in chickpea. LT affected male gamete development in a flower/anther age-dependent manner where outcome ranged from no pollen formation to pollen sterility or no anther dehiscence to delayed dehiscence. In anthers, LT inhibited microsporogenesis, microgametogenesis, tapetum degeneration, breakage of septum and stomium, and induced pollen sterility. Whereas disruption of male function was the prime cause of abortion in flowers below vacuolated pollen stage, flower abortion was due to a combination of male and female reproductive functions in flowers with mature pollen. The study will help in elucidating mechanisms governing flower development, anther and pollen development, and tolerance/susceptibility to LT.

Formation pattern in five types of pollen tetrad in Pseuduvaria trimera (Annonaceae).

In basal angiosperms, there are several types of permanent tetrad but their formation pattern remains elusive. Pseuduvaria trimera has five types of tetrads and is the species with the most abundant tetrad types in Annonaceae. In order to interpret the formation pattern of different tetrad types, pollen development was investigated from the microspore mother cell stage to the bicellular pollen stage and the ultrastructure of pollen wall in the five tetrad types using light microscopy, transmission electron microscopy, and confocal laser scanning microscopy. Both successive and intermediate cytokinesis were observed within the same anther. The nucleus location of the microspores together with cytokinesis determine the number and the spatial arrangement of callose plates, and further have an effect on the tetrad types. The anthers with or without septation and the arrangement of microsporocytes might be also related to the tetrad type. The individual pollen grains within the tetrads are connected with each other by crosswall cohesion and cytoplasmic channels at localized points in the proximal walls. The various types of tetrads, cytokinesis, and cohesion in P. trimera reflect the high diversity in pollen development, which enhances the dramatic variety in pollen morphology in this family. Our observations of the development of tetrads provided some new insights for interpreting the factors influencing the types of tetrads, and reported the existence of a cytoplasmic channel in Annonaceae for the first time.

The role of triploids in the origin and evolution of polyploids of Turnera sidoides complex (Passifloraceae, Turneroideae).

Triploids can play an important role in polyploid evolution. However, their frequent sterility is an obstacle for the origin and establishment of neotetraploids. Here we analyzed the microsporogenesis of triploids (x = 7) and the crossability among cytotypes of Turnera sidoides, aiming to test the impact of triploids on the origin and demographic establishment of tetraploids in natural populations. Triploids of T. sidoides exhibit irregular meiotic behavior. The high frequency of monovalents and of trivalents with non-convergent orientations results in unbalanced and/or non-viable male gametes. In spite of abnormalities in chromosome pairing and unbalanced chromosome segregation, triploids are not completely sterile and yielded up to 67% of viable pollen. Triploids that originated by the fusion of 2n × n gametes of the same taxon showed more regular meiotic behavior and higher fertility than triploids from the contact zone of diploids and tetraploids or triploids of hybrid origin. The reproductive isolation of T. sidoides cytotypes of different ploidy level is not strict and the 'triploid block' may be overcome occasionally. Triploids of T. sidoides produce diploid and triploid progeny suggesting that new generations of polyploids could originate from crosses between triploids or from backcrosses with diploids. The capability of T. sidoides to multiply asexually by rhizomes, would enhance the likelihood that a low frequency of neopolyploids can be originated and maintained in natural populations of T. sidoides.

An Introduction to Male Germline Development.

In this introductory chapter, we describe male germline development in plants taking Arabidopsis thaliana as a reference species. We first describe the transition from sporophytic to germline development, then microsporogenesis including meiosis, followed by male gametophyte development prior to pollination, and finally the progamic phase culminating in double fertilization, which leads to the formation of the embryo and the endosperm. For detailed information on some of these processes or on the molecular underpinning of certain fate transitions, we refer the reader to recent reviews. An important but often neglected aspect of male gametophyte development is the formation of the unique pollen cell wall. In contrast to that of other plant cells, the pollen cell wall is composed of two principal layers, the intine and exine. While the intine, the inner pecto-cellulosic cell wall layer, is biochemically and structurally similar to a "classical" plant cell wall, the exine is a unique composite with sporopollenin as its main component. Biosynthesis of the cell wall is remarkably similar between the spores of mosses and ferns, and pollen of seed plants, although slight differences exist, even between closely related species (reviewed in Wallace et al., AoB Plants 2011:plr027, 2011). In the latter sections of this chapter, we will present a brief overview of cell wall development in Arabidopsis pollen, where this aspect has been intensively studied.

Ultrastructural aspects of pollen ontogeny in an endangered plant species, Pancratium maritimum L. (Amaryllidaceae).

Pollen ontogeny in Pancratium maritimum L. was studied from the sporogenous cell to mature pollen grain stages using transmission electron, scanning electron, and light microscopy to determine whether the pollen development in P. maritimum follows the basic scheme in angiosperms or not. In the course of microsporogenesis and microgametogenesis, special attention was given to the considerable ultrastructural changes that are observed in the cytoplasm of microsporocytes, microspores, and mature pollen grains throughout the successive stages of pollen development. Microsporocyte differentiation concerning number and ultrastructure of organelles facilitates the transition of microsporocytes from the sporophytic phase to the gametophytic phase. However, cytoplasmic differentiation of generative and vegetative cells supports their functional distinctness and pollen maturation. Although microsporogenesis and microgametogenesis in P. maritimum generally follow the usual angiosperm pattern, abnormalities such as formation of unreduced gametes were observed. During normal microsporogenesis, meiocytes undergo meiosis and successive cytokinesis, resulting in the formation of isobilateral, decussate, and linear tetrads. Subsequent to the development of free and vacuolated microspores, the first mitotic division occurs and bicellular monosulcate pollen grains are produced. Pollen grains are shed from the anther at binucleate stage. During pollen ontogeny, three periods of vacuolization were observed: in meiocytes, in mononucleate free microspores, and in the generative cell.

Comprehensive transcriptome-based characterization of differentially expressed genes involved in microsporogenesis of radish CMS line and its maintainer.

Microsporogenesis is an indispensable period for investigating microspore development and cytoplasmic male sterility (CMS) occurrence. Radish CMS line plays a critical role in elite F1 hybrid seed production and heterosis utilization. However, the molecular mechanisms of microspore development and CMS occurrence have not been thoroughly uncovered in radish. In this study, a comparative analysis of radish floral buds from a CMS line (NAU-WA) and its maintainer (NAU-WB) was conducted using next generation sequencing (NGS) technology. Digital gene expression (DGE) profiling revealed that 3504 genes were significantly differentially expressed between NAU-WA and NAU-WB library, among which 1910 were upregulated and 1594 were downregulated. Gene ontology (GO) analysis showed that these differentially expressed genes (DEGs) were mainly enriched in extracellular region, catalytic activity, and response to stimulus. KEGG enrichment analysis revealed that the DEGs were predominantly associated with flavonoid biosynthesis, glycolysis, and biosynthesis of secondary metabolites. Real-time quantitative PCR analysis showed that the expression profiles of 13 randomly selected DEGs were in high agreement with results from Illumina sequencing. Several candidate genes encoding ATP synthase, auxin response factor (ARF), transcription factors (TFs), chalcone synthase (CHS), and male sterility (MS) were responsible for microsporogenesis. Furthermore, a schematic diagram for functional interaction of DEGs from NAU-WA vs. NAU-WB library in radish plants was proposed. These results could provide new information on the dissection of the molecular mechanisms underlying microspore development and CMS occurrence in radish.

A study on calcium oxalate crystals in Tinantia anomala (Commelinaceae) with special reference to ultrastructural changes during anther development.

Calcium oxalate (CaOx) crystals in higher plants occur in five forms: raphides, styloids, prisms, druses, and crystal sand. CaOx crystals are formed in almost all tissues in intravacuolar crystal chambers. However, the mechanism of crystallization and the role of CaOx crystals have not been clearly explained. The aim of this study was to explore the occurrence and location of CaOx crystals in organs of Tinantia anomala (Torr.) C.B. Clarke (Commelinaceae) with special attention to ultrastructural changes in the quantity of tapetal raphides during microsporogenesis. We observed various parts of the plant, that is, stems, leaves, sepals, petals, anthers, staminal trichomes and stigmatic papillae and identified CaOx crystals in all parts except staminal trichomes and stigmatic papillae in Tinantia anomala. Three morphological forms: styloids, raphides and prisms were found in different amounts in different parts of the plant. Furthermore, in this species, we identified tapetal raphides in anthers. The number of tapetal raphides changed during microsporogenesis. At the beginning of meiosis, the biosynthesis of raphides proceeded intensively in the provacuoles. These organelles were formed from the endoplasmic reticulum system. In the tetrad stage, we observed vacuoles with needle-shaped raphides (type I) always localised in the centre of the organelle. When the amoeboid tapetum was degenerating, vacuoles also began to fade. We observed a small number of raphides in the stage of mature pollen grains.

Evolutionary stasis in pollen morphogenesis due to natural selection.

The contribution of developmental constraints and selective forces to the determination of evolutionary patterns is an important and unsolved question. We test whether the long-term evolutionary stasis observed for pollen morphogenesis (microsporogenesis) in eudicots is due to developmental constraints or to selection on a morphological trait shaped by microsporogenesis: the equatorial aperture pattern. Most eudicots have three equatorial apertures but several taxa have independently lost the equatorial pattern and have microsporogenesis decoupled from aperture pattern determination. If selection on the equatorial pattern limits variation, we expect to see increased variation in microsporogenesis in the nonequatorial clades. Variation of microsporogenesis was studied using phylogenetic comparative analyses in 83 species dispersed throughout eudicots including species with and without equatorial apertures. The species that have lost the equatorial pattern have highly variable microsporogenesis at the intra-individual and inter-specific levels regardless of their pollen morphology, whereas microsporogenesis remains stable in species with the equatorial pattern. The observed burst of variation upon loss of equatorial apertures shows that there are no strong developmental constraints precluding variation in microsporogenesis, and that the stasis is likely to be due principally to selective pressure acting on pollen morphogenesis because of its implication in the determination of the equatorial aperture pattern.

Pollen and microsporangium development in Hovenia dulcis (Rhamnaceae): a different type of tapetal cell ultrastructure.

Despite that there is some literature on pollen morphology of Rhamnaceae, studies addressing general aspects of the microsporogenesis, microgametogenesis, and anther development are rare. The aim of this paper is to describe the ultrastructure of pollen grain ontogeny with special attention to tapetum cytology in Hovenia dulcis. Anthers at different stages of development were processed for transmission and scanning electron microscopy, bright-field microscopy, and fluorescence microscopy. Different histochemical reactions were carried out. The ultrastructural changes observed during the development of the tapetal cells and pollen grains are described. Large vesicles containing carbohydrates occur in the tapetal cell cytoplasm during the early stages of pollen development. Its origin and composition are described and discussed. This is the first report on the ontogeny and ultrastructure of the pollen grain and related sporophytic structures of H. dulcis.

Ultrastructure of microsporogenesis and microgametogenesis in Brachypodium distachyon.

Brachypodium distachyon has emerged as a model system for forage grass and cereal grain species. Here, we report B. distachyon pollen development at the ultrastructural level. The process of microsporogenesis and microgametogenesis in B. distachyon follows the typical angiosperm pollen development sequence. Pronounced evaginations of the nuclear envelope are observed prior to meiosis, indicating active nucleocytoplasmic exchange processes. The microspore mother cells undergo meiosis and subsequent cytokinesis, forming isobilateral tetrads. Following dissolution of the callose wall and release of free and vacuolated microspores, mitotic divisions lead to the formation of mature, three-celled pollen grains. In B. distachyon, pollen wall formation begins at the tetrad stage by the formation of the exine template (primexine). The exine is tectate-columellate, comprising a foot layer and endexine. Development of the tectum and the foot layer is complete by the free microspore stage of development, with the tectum formed discontinuously. The endexine initiates in the free microspore stage but becomes compressed in mature grains. The intine layer is deposited after mitosis and comprises three layers during the mature pollen stage of development. Pore development initiates during early free microspore development stage and Brachypodium pollen has a single germination pore consisting of a slightly raised annulus surrounding a central operculum. The tapetum is of the secretory type with loss of the tapetal cell walls beginning at about the time of microsporocyte meiosis. This is the first report on ultrastructure of microsporogenesis and microgametogenesis in B. distachyon. In general, Brachypodium microsporogenesis and microgametogenesis conform to a typical grass pollen development pattern.

Arabidopsis CHROMOSOME TRANSMISSION FIDELITY 7 (AtCTF7/ECO1) is required for DNA repair, mitosis and meiosis.

The proper transmission of DNA in dividing cells is crucial for the survival of eukaryotic organisms. During cell division, faithful segregation of replicated chromosomes requires their tight attachment, known as sister chromatid cohesion, until anaphase. Sister chromatid cohesion is established during S-phase in a process requiring an acetyltransferase that in yeast is known as Establishment of cohesion 1 (Eco1). Inactivation of Eco1 typically disrupts chromosome segregation and homologous recombination-dependent DNA repair in dividing cells, ultimately resulting in lethality. We report here the isolation and detailed characterization of two homozygous T-DNA insertion mutants for the Arabidopsis thaliana Eco1 homolog, CHROMOSOME TRANSMISSION FIDELITY 7/ESTABLISHMENT OF COHESION 1 (CTF7/ECO1), called ctf7-1 and ctf7-2. Mutants exhibited dwarfism, poor anther development and sterility. Analysis of somatic tissues by flow cytometry, scanning electron microscopy and quantitative real-time PCR identified defects in DNA repair and cell division, including an increase in the area of leaf epidermal cells, an increase in DNA content and the upregulation of genes involved in DNA repair including BRCA1 and PARP2. No significant change was observed in the expression of genes that influence entry into the endocycle. Analysis of meiocytes identified changes in chromosome morphology and defective segregation; the abundance of chromosomal-bound cohesion subunits was also reduced. Transcript levels for several meiotic genes, including the recombinase genes DMC1 and RAD51C and the S-phase licensing factor CDC45 were elevated in mutant anthers. Taken together our results demonstrate that Arabidopsis CTF7/ECO1 plays important roles in the preservation of genome integrity and meiosis.

Variation of microsporogenesis in monocots producing monosulcate pollen grains.

BACKGROUND AND AIMS: Microsporogenesis leading to monosulcate pollen grains has already been described for a wide range of monocot species. However, a detailed study of additional callose deposition after the completion of the cleavage walls has been neglected so far. The study of additional callose deposition in monosulcate pollen grain has gained importance since a correlation between additional callose deposition and aperture location has recently been revealed. METHODS: Microsporogenesis is described for 30 species belonging to eight families of the monocots: Acoraceae, Amaryllidaceae, Alstroemeriaceae, Asparagaceae, Butomaceae, Commelinaceae, Liliaceae and Xanthorrhoeaceae. KEY RESULTS: Five different microsporogenesis pathways are associated with monosulcate pollen grain. They differ in the type of cytokinesis, tetrad shape, and the presence and shape of additional callose deposition. Four of them present additional callose deposition. CONCLUSIONS: In all these different microsporogenesis pathways, aperture location seems to be linked to the last point of callose deposition.

Caracterização citogenética para identificação dos níveis de ploidia em cinco espécies do gênero Mentha L / Citogenetic characterization to determination of ploidy level on five Mentha L. species

Neste trabalho foi feita a caracterização citogenética da: microsporogênese, tétrades, estimativa da viabilidade do pólen pelo método de coloração e contagem do número máximo de nucléolos por célula interfásica, para identificação dos níveis de ploidia, em cinco espécies do gênero Mentha L. Foram coletadas inflorescências em 30 plantas de cada espécie, em duas florações sucessivas, nos anos 2006 e 2007. As inflorescências foram tratadas em etanol-ácido acético (3:1), em temperatura ambiente durante seis horas, transferidas para álcool 70% (v/v) e conservadas em geladeira até análise. Nas análises da microsporogênese, tétrades e pólen o corante usado foi carmin propiônico 2% e na identificação dos nucléolos nitrato de prata (AgNO3). Os resultados demonstraram que as cinco espécies são poliplóides. M. crispa heptaplóide (2n=7x=84) com 11 nucléolos, M. spicata tetraplóide (2n=4x=48) com 8 nucléolos, M.x gentilis pentaplóide (2n=5x=60) com 12 nucleólos, M. piperita e M.x piperita ambas hexaplóides (2n=6x=72) com 8 e 9 nucléolos respectivamente. M. spicata e M. crispa mantiveram as mais altas porcentagens de células normais na microsporogênese, na formação de tétrades e na estimativa da viabilidade do pólen por coloração, sugerindo maior estabilidade meiótica quando comparados aos demais poliplóides estudados.

The cytogenetic characterization of five species of Mentha L. genus, including the data: regularity of microsporogenesis and tetrads, and polen viability, using the coloration method and the counting of the maximum number of nucleolus by interphasic cell were carried out in this study to identify the ploid levels. These analyses were performed from inflorescences collected in 30 plants of each species, during two successive florations in 2006 and 2007. Inflorescences were treated in 3:1 ethanol:acetic acid mixture at room temperature during six hours, then transferred to 70%(v/v) ethanol solution and refrigerated until the analysis. For microsporogenis, tetrad and pollen analysis, we used carmine propionic 2% (m/v) and for nucleolus identification, we used AgNO3 solution. It was possible to observe that all five species were polyploids. M. crispa heptaploid (2n=7x=84) with 11 nucleolus, M. spicata tetraploid (2n=4x=48) with 8 nucleolus, M. x gentilis pentaploid (2n=5x=60) with 12 nucleolus, M. piperita and M. x piperita both hexaploid (2n=6x=72) with 8 and 9 nucleolus respectively. M. spicata and M. crispa kept the highest percentual values of normal cells in microsporogenesis as well as in tetrads formation and pollen viability, suggesting a higher meiotic stability when compared to the other polyploids studied.

Abnormal behavior of spindle during microsporogenesis of passiflora (passifloraceae) / Comportamento anormal de fuso durante a microsporogênese de passiflora (passifloraceae)ien

Passiflora genus, Passifloraceae family, has more than 500 species and 120 of them are native species of Brazil. All species produce fruits that are used as food, medicine and decoration. Floral buttons of five species were collected and fixed in a mixture of ethanol and acetic acid (3:1). The slides were prepared by squashing and staining with 1% propionic carmine. Results showed that during microsporogenesis there were few irregularities, mostly frequently related to chromosome irregular segregation as: precocious migration to poles in metaphase I and II, non-oriented bivalent chromosomes at metaphase I and II, and laggard chromosomes in anaphase I and II, forming micronuclei in telophases I and II and tetrad with microcyte. Another observed irregularity is related to the organization of spindle fibers in meiosis II as they organize themselves in T and V shapes and in sequential spindle. However, in the V-shaped spindle configuration, there was fusion between two nuclei that were close, forming triads instead of tetrads. Irregular chromosome segregation, abnormal spindles and irregularities in the cytokinesis process were responsible for the formation of monads, dyads, triads and polyads. However, the pollen grain viability was not harmed, presenting an 83.98% to 98.59% fertility variation.

O gênero Passiflora, família Passifloraceae, apresentam mais de 500 espécies, havendo no Brasil aproximadamente 120 espécies nativas. Todas as espécies produzem frutos que são utilizados como produtos alimentícios, medicinais e ornamentais. Botões florais de cinco espécies foram coletados e fixados em etanol/acido acético (3:1). As lâminas foram preparadas utilizando a técnica de esmagamento e coradas com carmim propiônico a 1%. Como resultado, observou-se que durante a microsporogênese poucas irregularidades foram encontradas, as mais frequentes estão relacionadas à segregação irregular dos cromossomos, tais como: migração precoce para os pólos em metáfase I e II, bivalente não orientado em metáfase I e II, e cromossomos retardatários em anáfase I e II, levando a formação de micronúcleos em telófases I e II, e micrócito em tétrades. Outra irregularidade observada esta relacionada a organização das fibras dos fusos em meiose II, que se organizam na forma em T, em V e fuso sequencial. Na configuração de fuso na forma de V ocorreu fusão entre dois núcleos que estavam próximos, formando tríade ao invés de tétrade. A segregação irregular dos cromossomos, a formação de fusos anormais e as irregularidades no processo de citocinese foram responsáveis pela formação de mônades, díades, tríades e políades como produtos final da meiose. Porém, a viabilidade dos grãos de pólen não foi comprometida, apresentado uma variação de 83,98% a 98,59% de fertilidade.

Anther and pollen development in some species of Poaceae (Poales) / Desenvolvimento da antera e do grão de pólen em espécies de Poaceae (Poales)

Anther and pollen development were studied in Olyra humilis Nees, Sucrea monophylla Soderstr, (Bambusoideae), Axonopus aureus P. Beauv., Paspalum polyphyllum Nees ex Trin. (Panicoideae), Eragrostis solida Nees, and Chloris elata Desv. (Chloridoideae). The objective of this study was to characterise, embryologically, these species of subfamilies which are considered basal, intermediate and derivate, respectively. The species are similar to each other and to other Poaceae. They present the following characters: tetrasporangiate anthers; monocotyledonous-type anther wall development, endothecium showing annular thickenings, secretory tapetum; successive microsporogenesis; isobilateral tetrads; spheroidal, tricellular, monoporate pollen grains with annulus and operculum. Nevertheless, the exine patterns of the species studied are distinct. Olyra humilis and Sucrea monophylla (Bambusoideae) show a granulose pattern, whereas in the other species, it is insular. In addition, Axonopus aureus and Paspalum polyphyllum (Panicoideae) have a compactly insular spinule pattern, while Chloris elata and Eragrostis solida (Chloridoideae) show a sparsely insular spinule pattern. The exine ornamentation may be considered an important feature at the infrafamiliar level.

O desenvolvimento da antera e do grão de pólen de Olyra humilis Nees, Sucrea monophylla Soderstr. (Bambusoideae), Axonopus aureus P. Beauv., Paspalum polyphyllum Nees ex Trin. (Panicoideae), Eragrostis solida Nees and Chloris elata Desv. (Chloridoideae) foi estudado visando caracterizar embriologicamente essas espécies de subfamílias consideradas basal, intermediária e derivada, respectivamente. As espécies são similares entre si e entre as demais Poaceae. Apresentam os seguintes caracteres: anteras tetrasporangiadas; desenvolvimento da parede da antera do tipo monocotiledôneo, endotécio com espessamento de parede anelar, tapete secretor; microsporogênese sucessiva; tétrades isobilaterais; grãos de pólen esféricos, tricelulares, monoporados, com anel e opérculo. Por outro lado, o padrão de ornamentação da exina do grão de pólen é distinto. Olyra humilis e Sucrea monophylla (Bambusoideae) apresentam padrão granuloso e as demais espécies padrão insular. Axonopus aureus e Paspalum polyphyllum (Panicoideae) apresentam espínulos densamente agrupados, enquanto Chloris elata e Eragrostis solida (Chloridoideae) espínulos esparsamente agrupados. A ornamentação da exina dos grãos de pólen pode ser considerada caráter importante a nível infrafamiliar.