Meiosis In Microspore Mother Cells Research Articles

Alternative Splicing of OsRAD1 Defines C-Terminal Domain Essential for Protein Function in Meiosis

Alternative splicing can generate multiple mRNAs that differ in their untranslated regions or coding sequences, and these differences might affect mRNA stability or result in different protein isoforms with diverse functions and/or localizations. In this study, we isolated a sterile mutant in rice with abnormal meiosis of microspore mother cells and megaspore mother cells that carried a point mutation in OsRAD1 gene. Cloning of OsRAD1 cDNAs revealed three transcript variants, named as OsRAD1.1, OsRAD1.2 and OsRAD1.3, respectively, which were derived from alternative splicing of the last intron. Proteins derived from the three transcripts were mostly identical except the difference in the very C-terminal domain. The three transcripts exhibited similar expression patterns in various tissues, but the expression level of OsRAD1.1 was the highest. Specific knockout of OsRAD1.1 led to sterility, while knockout of OsRAD1.2 and OsRAD1.3 together did not change the plant fertility. Overexpression of OsRAD1.2 and OsRAD1.3 cDNAs in OsRAD1.1-specific mutant did not complement the plant fertility. Yeast two-hybrid assay showed that OsRAD1.1, but not OsRAD1.2 and OsRAD1.3, interacted with the three other meiosis proteins OsHUS1, OsRAD9 and OsRAD17, suggesting that the C-terminal domain of OsRAD1.1 is critical for the protein function.

Cellular and molecular characteristics of pollen abortion in chrysanthemum cv. Kingfisher.

Microspore degeneration at the tetrad stage is associated with tapetum degeneration retardation. Some genes and proteins related to cell senescence and death are the key factors for pollen abortion. Chrysanthemum (Chrysanthemum morifolium) is a major floriculture crop in the world, but pollen contamination is an urgent problem to be solved in chrysanthemum production. C. morifolium 'Kingfisher' is a chrysanthemum cultivar that does not contain any pollen in mature anthers, thus it is a very important material for developing chrysanthemum without pollen contamination. However, the mechanism of its pollen abortion remains unclear. In this study, the cellular and molecular mechanisms of 'Kingfisher' pollen abortion were investigated using transmission electron microscopy, RNA sequencing, isobaric tags for relative and absolute quantitation, and bioinformatics. It was found that the meiosis of microspore mother cells was normal before the tetrad stage, the microspores began to degenerate at the tetrad stage, and no microspores were observed in the anthers after the tetrad stage. In addition, transcriptomic and proteomic analyses showed that some genes and proteins related to cell senescence and death were identified to be implicated in chrysanthemum pollen abortion. These results indicated that the tetrad stage was the main period of pollen abortion, and the genes and proteins related to cell senescence and death contributed to pollen abortion. These add to our understanding of chrysanthemum pollen abortion and will be helpful for development of flowers without pollen contamination in the future.

OsFTIP7 determines auxin-mediated anther dehiscence in rice.

Anther dehiscence determines successful sexual reproduction of flowering plants through timely release of pollen grains for pollination and fertilization. Downregulation of auxin levels during pollen mitosis is essential for promoting anther dehiscence along with pollen maturation. How this key transition of auxin levels is regulated in male organs remains elusive. Here, we report that the rice FT-INTERACTING PROTEIN 7 is highly expressed in anthers before pollen mitotic divisions and facilitates nuclear translocation of a homeodomain transcription factor, Oryza sativa homeobox 1, which directly suppresses a predominant auxin biosynthetic gene, OsYUCCA4, during the late development of anthers. This confers a key switch of auxin levels between meiosis of microspore mother cells and pollen mitotic divisions, thus controlling the timing of anther dehiscence during rice anthesis. Our findings shed light on the mechanism of hormonal control of anther dehiscence, and provide a new avenue for creating hormone-sensitive male sterile lines for hybrid plant breeding.

Anther structure and pollen development in Melicoccus lepidopetalus (Sapindaceae): An evolutionary approach to dioecy in the family

Anther and pollen development in staminate and pistillate flowers of dioecious Melicoccus lepidopetalus (Sapindaceae) were examined by light and electron microscopy. Young anthers are similar in both types of flowers; they consist of epidermis, endothecium, two to four middle layers and a secretory tapetum. The microspore tetrads are tetrahedral. The mature anther in staminate flowers presents compressed epidermal cells and endothecium cells with fibrillar thickenings. A single locule is formed in the theca by dissolution of the septum and pollen grains are shed at two-celled stage. The mature anthers of pistillate flowers differ anatomically from those of staminate flowers. The epidermis is not compressed, the endothecium does not develop fibrillar thickenings, middle layers and tapetum are generally persisting, and the stomium is nonfunctional. Microspore degeneration begins after meiosis of microspore mother cells. At anthesis, uninucleate microspores and pollen grains with vegetative and generative nuclei with no cytokinesis are observed. Some pollen walls display an abnormal exine deposition, whereas others show a well formed exine, although both are devoid of intine. These results suggest that in the evolution towards unisexuality, the developmental differences of anther wall tissues and pollen grains between pistillate and staminate flowers might become more pronounced in a derived condition, such as dioecy.

Microsporogenesis and development of the male gametophyte in Allium senescens L. (Liliaceae) in China

Microsporogenesis and development of the male gametophyte of Allium senescens L. were studied by use of paraffin sections. The anther was found to be four-sporangia. Its wall includes four layers: epidermis, endothecium, middle layer, and secretory tapetum. Cytokinesis during meiosis of microspore mother cells (MMCs) is successive. Most mature pollen grains are two-celled, a few are three-celled. In addition, anomalies were observed during meiosis of MMC and in uninucleate microspores, including laggard chromosomes, lagging chromosomes, anaphase bridges, and micronucleus. These anomalies are possible reasons for abortive pollen.

Distribution of Starch and Neutral Lipids in the Developing Anthers ofLpomoea cairica

The Periodic Acid-Schiff (PAS) reaction was used to test for the presence of starch, and Sudan black was applied to detect neutral lipids (lipid drops) during anther development in Ipomoea cairica. Starch was observed in sporogenous and anther wall cells. Prior to meiosis in microspore mother cells (MMCs), starch was not evident, although small lipid drops appeared. A substantial amount of starch accumulated in the epidermal and endothecium cells, but starch and lipid drops were not identified in the tapetum. At the tetrad stage, starch appeared in microspores, and the amount of starch remained constant in anther cells. Early in the microspore stage, the tapetum degenerated, starch remained in the microspores, and lipid drops were completely lost. A large and conspicuous vacuole was formed in the microspores and lipid drops reformed in the cells at the late microspore stage. Following microspore division, the vegetative cell of bicellular pollen grains was filled with starch and lipid drops, and the inner middle layer degenerated. Finally, at anthesis, lipid drops and starch constituted the stored nutritive material in the mature pollen.

Microsporogenesis in Rauvolfia serpentina (L.) Benth ex Kurz (Apocynaceae): An evidence for dual cytokinesis in microspore mother cells

Rauvolfia serpentina is being used worldwide for its extensive medicinal value. A very few studies were done about microsporogenesis and male gametophyte formations in R. serpentina and they lack in accurate information about it. The aim of the present study was to give accurate information regarding microsporogenesis and male gametophyte formations in R. serpentina. Results explain the most important characteristic features ofR. serpentina that was tetrasporangiate anther, dicotyledonous type of anther wall formation, the occurrence of both successive and simultaneous cytokinesis during the meiosis in microspore mother cells, uninucleate and highly vacuolated glandular tapetum, tetrahedral, tetragonal and decussate pollen tetrad and three-celled mature pollen grain during shedding time. These results were compared and discussed with other previous studies about Rauvolfia. Some of the studies contradicted with each other in terms of anther development and microsporogenesis, within genus and even in the species R.serpentina. Through this study, we clarified all these controversial information of microsporogenesis and concluded that R. serpentina undoubtedly follows both successive and simultaneous cytokinesis. Appearance of both types of cytokinesis is common inRauvolfia, even though simultaneous is prevalent. Key words: Rauvolfia serpentine, Apocynaceae, microsporogenesis, simultaneous cytokinesis, successive cytokinesis.

Cryptic dioecy in Mussaenda pubescens (Rubiaceae): a species with stigma-height dimorphism.

Evolutionary transitions from heterostyly to dioecy have been proposed in several angiosperm families, particularly in Rubiaceae. These transitions involve the spread of male and female sterility mutations resulting in modifications to the gender of ancestral hermaphrodites. Despite sustained interest in the gender strategies of plants, the structural and developmental bases for transitions in sexual systems are poorly understood. Here, floral morphology, patterns of fertility, pollen-tube growth and floral development are investigated in two populations of the scandent shrub Mussaenda pubescens (Rubiaceae), native to southern China, by means of experimental and open-pollinations, light microscopy, fluorescence microscopy and scanning electron microscopy combined with paraffin sectioning. Mussaenda pubescens has perfect (hermaphroditic) flowers and populations with two style-length morphs but only weak differentiation in anther position (stigma-height dimorphism). Experimental pollinations demonstrated that despite morphological hermaphroditism, the species is functionally dioecious. The long-styled (L) morph possesses sterile pollen and functions as a female, whereas the short-styled (S) morph is female sterile and functions as a male. Self- and intra-morph pollinations of the S-morph were consistent with those expected from dimorphic incompatibility. The two populations investigated were both S-morph (male) biased. Investigations of early stages of floral development indicated patterns typical of hermaphroditic flowers, with no significant differences in organ growth between the floral morphs. Meiosis of microspore mother cells was of the simultaneous type with tetrads isobilateral in shape. The tapetal cells in anther walls of the L-morph became vacuolized during meiosis I, ahead of the uninucleate microspore stage in the S-morph. In the L-morph, the microspore nucleus degenerated at the tetrad stage resulting in male sterility. Microsporogenesis and male gametophyte development was normal in the S-morph. Failure in the formation of megaspore mother cells and/or the development of megagametophytes resulted in female sterility in the S-morph, compared with normal megasporogenesis in the L-morph. In M. pubescens, cryptic dioecy has evolved from stigma-height dimorphism as a result of morph-specific sterility mutations.

Calcium Distribution in Developing Anthers of Lettuce (Lactuca sativa)

Potassium antimonite was used to locate calcium in the anthers of lettuce (Lactuca sativa). There are no calcium precipitates in young anthers. After meiosis of microspore mother cells, calcium precipitates first appear in the tapetal cells, from which some small secretive vesicles containing many calcium precipitates are secreted into the locule. At a late stage of the microspore, tapetal cells completely degenerate and their protoplasts move into the locule with many calcium precipitates. The calcium precipitates increase in the early microspores, and in the exine. When the microspores form some small vacuoles containing calcium precipitates, and those vacuoles then fuse to form a large one, the calcium precipitates evidently decrease. The large vacuole of bicellular pollen grain discomposes and calcium precipitates again appear in the cytoplasm and then decrease. When the pollen matures, most calcium precipitates are located in its exine with only a few in the cytoplasm.

Differential expression of proteins in the wild type and 7B-1 male-sterile mutant anthers of tomato (Solanum lycopersicum): A proteomic analysis

In the 7B-1 male-sterile mutant of tomato, pollen development breaks down prior to meiosis in microspore mother cells (MMCs). We have used the proteomic approach to identify differentially expressed proteins in the wild type (WT) and mutant anthers with the objective of analyzing their roles in normal pollen development and in male sterility. By using 2-DE and DIGE technologies, over 1800 spots were detected and of these 215 spots showed 1.5-fold or higher volume ratio in either WT or 7B-1 anthers. Seventy spots, either up-regulated in WT, or in 7B-1, were subjected to mass spectrometry and 59 spots representing 48 distinct proteins were identified. The proteins up-regulated in WT anthers included proteases, e.g., subtilase, proteasome subunits, and 5B-protein with potential roles in tapetum degeneration, FtsZ protein, leucine-rich repeat proteins, translational and transcription factors. In 7B-1 anthers, aspartic protease, superoxide dismutase, ACP reductase, ribonucleoprotein and diphosphate kinase were up-regulated. Also, cystatin inhibitory activity was high in the mutant and correlated with the expression of male sterility. Other proteins including calreticulin, Heat shock protein 70, glucoside hydrolase, and ATPase, were present in both genotypes. The function of identified proteins in tapetum and normal pollen development, and in male sterility is discussed.

Embryology of Hortonioideae and Monimioideae (Monimiaceae, Laurales): characteristics of the ‘lower’ monimioids

We investigated the embryology of the ‘lower’ monimioids, i.e. Monimioideae (Monimia, Palmeria and Peumus) and Hortonioideae (Hortonia), which are poorly described embryologically. Our results show that, contrary to what has been reported in the literature, ‘lower’ monimioids show very little variation in their embryological characters. Comparisons with Mollinedioideae (a large derived subfamily in Monimiaceae) and other families in Laurales show that the ‘lower’ monimioids are relatively consistent in sharing predominantly isobilateral tetrads of microspores and megaspores, a non-specialized chalaza, and a mesotestal–endotestal seed coat (with tracheoidal cells of the meso- and endotesta). It is likely that, while the shared successive cytokinesis during meiosis of microspore mother cells supports the Monimiaceae–Hernandiaceae–Lauraceae clade obtained by molecular evidence, no synapomorphies exist to support a sister-group relationship of Monimiaceae with Hernandiaceae or Lauraceae. Instead, the lack of hypostase in ovules and/or young seeds, the lack of endosperm in mature seeds and the amoeboid tapetum in the anther are likely synapomorphies of Hernandiaceae and Lauraceae. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 228–241.

Floral structure and development in the dioecious Australian endemic Lomandra longifolia (Lomandraceae)

The micromorphology and histology of the development of male and female flowers of the dioecious Australian endemic species Lomandra longifolia Labill. was studied by means of scanning electron microscopy and light microscopy of entire and sectioned material. Although mature flowers are functionally unisexual, in the early stages of development pistillate and staminate flowers are identical and apparently bisexual. In a sequential fashion, six perianth parts are initiated within two alternating whorls, the sepals first and the petals second; six stamens are initiated in two alternating whorls of three stamens each, the first opposite the sepals and the second opposite the petals; and last, a central gynoecium is initiated. Following initiation, the two flower types diverge developmentally when the stamens become bilobed. In male flowers, cytological analysis of the slowly growing abortive pistil shows that megasporogenesis does not occur. Pistil abortion happens before meiosis whereas the stamens continue to develop until maturity and dehiscence. In female flowers, stamen arrest occurs before the onset of meiosis in microspore mother cells, after which the pistil continues its development through megasporogenesis and megagametogenesis. In all, 14 stages of floral development of both male and female flowers have been designated. Stages 1–6 of the two flower types were common to both sexes.

Embryological Studies on Narcissus tazetta var. chinensis

Chinese narcissus (Narcissus tazetta var. chinensis Roem) blooms but has no seeds. Embryological studies on the species were conducted to discover the causes of its sterility. Its anther wall is composed of four layers of cells, and its tapetum is of the secretory type. The cytokinesis of microspore mother cells is of the successive type, and the tetrad is tetrahedral. During meiosis of microspore mother cells, some chromosomes lagged, and several micronuclei were found in tetrads. Only 27.7% of the pollen grains contained full cytoplasm, and 1.3% of them germinated in culture medium. No pollen grain, however, could germinate on the stigma. The ovary is trilocular with axile placenta, and the ovules are bitegmic, tenuinucellate, and anatropous. Its embryo sac is of the polygonum type. Most embryo sacs degenerated, and only about 4.5% of the ovules contained a normal embryo sac with an egg cell, two synergids, three antipodal, and a central cell containing two polar nuclei. One reason for the sterility of Chinese narcissus is the abnormality of microsporogenesis and megasporogenesis, in which only a few functional pollen grains and embryo sacs are produced. The other reason is that the pollen grains cannot germinate on the stigma.

Microsporogenesis and pollen development in Leymus chinensis with emphasis on dynamic changes in callose deposition

Leymus chinensis is an economically and ecologically important grass that exhibits low seed production. To better understand the causes of its low sexual reproductivity, the microsporogenesis and pollen development of this species were investigated, with emphasis on dynamic changes in callose deposition. A variety of histochemical stains were employed, including Heidenhain's hematoxylin, decolorized aniline blue, DAPI, and acetocarmine, along with a temporary mount method. Microsporogenesis and pollen development generally took place from June 12 to 26. The meiosis of microspore mother cells (MMCs) was of the successive type and the tetrad was isobilateral in shape. Mature pollen grains comprised two sperms and a vegetative nucleus. Callose initially appeared in the center of the anther locule at the premeiotic phase, and then gradually and unevenly deposited around the MMC before the commencement of meiosis. At the onset of meiosis, the accumulation of callose enclosing the MMC peaked, accompanied by the disappearance of callose in the center of the locule. At the dyad and tetrad stages, the dyads and tetrads were surrounded by callose wall and the microspores in the tetrads were isolated by a crossed cell plate composed of callose. Microspores just released from tetrads were still enclosed in callose wall, and then callose gradually disappeared in the pollen wall. Ultimately, callose almost completely disappeared from the walls of mature pollen grains. In the large numbers of sections observed, most of the cases of meiosis of the MMCs, pollen development, and callose dynamics were normal, with only a few abnormities observed. The results suggest that microsporogenesis, male gametogenesis, and callose dynamics during these processes are generally normal in this species, and that the callose wall plays an important role in the production of functional pollen grains. The small numbers of abnormities of these processes that occurred likely do not adversely affect the production of viable pollen grains. Therefore, microsporogenesis and pollen development may not be factors in the low seed production of L. chinensis.

Chromosome Behavior During Meiosis and Development of Spore Mother Cells in the Chinese Quillwort Isoetes sinensis T. C. Palmer (Isoetaceae)

Abstract Chromosome behavior during meiosis of the tetraploid Isoetes sinensis was observed to be similar to that of basic diploid Isoetes species. This observation was consistent with the previous report that polyploid species of Isoetes are allopolyploids. Meiosis was generally similar in both megaspore and microspore mother cells, but differences were observed. Due to the smaller size of the microspore mother cells, during prophase I, chromosomes are not as dispersed as those in megaspore mother cells. Cytomixis was observed in all stages of meiosis in microspore mother cells, but it was not seen at any stage of meiosis in megaspore mother cells. Cytomixis, lagging chromosomes, chromosome bridges, chromosome fragments, and micronuclei, observed during meiosis in I. sinensis, can affect sexual reproduction, but it does not appear to be a major cause of population decline in this species. The major cause of decline is habitat degradation from human disturbance. The few remaining populations of the Chines...

Early signs of disruption of wheat anther development associated with the induction of male sterility by meiotic-stage water deficit

Water deficit during meiosis in microspore mother cells of wheat (Triticum aestivum L.) induces male sterility, which reduces grain yield. In plants stressed during meiosis and then re-watered, division of microspore mother cells seems to proceed normally, but subsequent pollen development is arrested. Stress-affected anthers generally lack starch. We employed light microscopy in conjunction with histochemistry to compare the developmental anatomy of water-stress-affected and normal anthers. The earliest effects of stress, detectable between meiosis and young microspore stages, were the degeneration of meiocytes, loss of orientation of the reproductive cells, and abnormal vacuolization of tapetal cells. Other effects observed during subsequent developmental stages were deposition of starch in the connective tissue where it is normally not present, hypertrophy of the middle layer or endothecial cells, and deposition of sporopollenin-like substances in the anther loculus. The resulting pollen grains lacked both starch and intine. These results suggest that abnormal degeneration of the tapetum in water-stressed anthers coupled with a loss of orientation of the reproductive cells could be part of early events leading to abortion of microspores.

Chromosome numbers and a new model for karyotype evolution in Ruppia L. (Ruppiaceae)

Populations of three species in the genus Ruppia that inhabit the western part of the Mediterranean region were studied caryologically. All three species present bimodal karyotypes. Ruppia drepanensis Tineo ex guss. (2 n=20) has a karyotype asymmetry of the 2C type. Ruppia cirrhosa (Petagna) Grande and Ruppia maritima L. (both with 2 n=40) present a 2B asymmetry. Observations of meiosis of microspore mother cells revealed that R. drepanensis forms ten bivalents at diakinesis and Metaphase I. The other two species exhibit 20 bivalents. The long arm of subtelocentric, large chromosomes in all three species shows no sign of chiasmata at meiosis.

Cell differentiation in microsporangia of Pinus sylvestris. III. Late pachytene

Cycles of hyperactivity were observed in tapetal and microspore mother cells of Pinus sylvestris L. during the pachytene stage of meiosis in microspore mother cells. Hyperactive periods were characterized by dilated rough ER, hypersecretory dictyosomes, autophagic vesicles having one to two sequestration envelopes, and maze‐like whor‐les of the endomembrane system. The extent and sequence of differentiation differed between the two cell types. During distinct phases of development there was either fi‐brillar flocculent or lipoidal material or both within dilations and at cell surfaces. Tapetal cell transfer of material involved endocytotic and exocytotic vesicles and channels opening directly to the cell surface. Dilations of the nuclear envelope of microspore mother cells in late pachytene intruded into the nucleus and, in conjunction with dilated ER, dominated cell profiles. Cellular morphogenesis in a microspo‐rangium was seldom synchronous except for intervals of dedifferentiation when plas‐modesma‐like connections were formed between tapetal cells. Cycles of differentiation and dedifferentiation were correlated each spring season for five years with the progressive change of pachytene chromosomes, suggesting control by a genetic program rather than annual variations in the environment.

The Bases of Angiosperm Phylogeny: Embryology

Many of the embryological characteristics that may be useful, when employed judiciously and in conjunction with other characters, in arriving at taxonomic conclusions are listed. Several characteristics that show a non-random distribution between families of the Magnoliatae and those of the Liliatae are discussed. Features which are more predominant in the monocotyledons than dicotyledons are: monocotyledonous type of development of the anther wall; amoeboid tapetum; successive cytokinesis of the microspore mother cells to form isobilateral tetrads; helobial endosperm development; and a single cotyledon in the mature embryo. In contrast, those characteristics that are more prevalent among dicot families than monocot families include: basic and dicotyledonous patterns of anther wall formation; simultaneous cytokinesis of microspore mother cells with the formation of tetrahedral tetrads; hemitropous, amphitropous, or circinotropous ovules; ovules with a single integument; an endothelium; Oenothera, Penaea, Peperomia, Plumbago, or Plumbagella types of megagametophyte development; cellular endosperm; and two cotyledons in the mature embryo. In spite of these differences, those characteristics that are most common-occurring in at least 70%, and usually more, of all angiosperms -are evenly distributed between the two classes and afford a strong embryological unity to the angiosperms. These widespread characters include: four microsporangia per anther; differentiated endothecium; two-celled pollen grains; bitegmic anatropous ovules; Polygonum type of megagametophyte development; and nuclear endosperm. Within the two classes distribution of the various characters is not always proportional among the several subclasses and superorders; for example, a unitegmic, tenuinucellate ovule with an endothelium, cellular endosperm with haustoria and Solanad embryogeny predominates in the Ericanae and Asteridae; or helobial endosperm is a distinctive feature of the Alismidae. On the whole, embryological characteristics are remarkably constant at the family level. In those families where variation does occur, genera are usually constant, although a few notable examples of intrageneric, and even intraspecific, variation do exist, as for example, in patterns of megagametophyte development. In addition to the taxonomic usefulness of the grosser aspects of embryology-the major categories of structure or development-some evidence is presented suggesting that variation in details within a single category, such as size, shape, and cellular characteristics of the developing and mature megagametophyte, may be helpful in determining relationships within families, genera, or species. I Since the time of the nineteenth century landmarks in embryological knowledge and the men who made the observations (Amici's discovery of the pollen tube, Hofmeister's recognition of the general structure of the mature megagametophyte and meiosis in microspore mother cells, Strasburger's working out of stages in megagametophyte development and observation of fertilization, and finally the independent recognition that fertilization was double by Nawaschin and Guignard [see Maheshwari, 1950]), many descriptions of various aspects of sexual reproduction (embryology in the broad sense) in a wide variety of angiosperm plants have been published by a host of botanists. During the early part of this century some use was made of embryological characteristics for systematic purposes, for example, Samuelsson's (1913) treatment of the Ericaceae, but it was only with the publication of Schnarf's (1931) Vergleichende Embryologie der Angiospernen that impetus was given to this type of synthesis of the accumulating embryological information. Since that time a number of papers, review articles, or books have