Course Of Microsporogenesis Research Articles

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.

Evaluation of the course of microsporogenesis in some selected peach (Prunus persica L./Batsch) cultivars

The evaluation of the microsporogenesis process was performed from January to April within the period of 2011-2013. The experiment involved 15 peach cultivars and the control cultivar Redhaven. The course of microsporogenesis was evaluated on the base of microscopic observations. It was found out that cultivars under study differed not only in the total length of microsporogenesis but also in dates of the onset of individual developmental stages. The shortest period of the development of pollen grains was detected in the cultivar W 13 (viz. 89 days) while the longest ones were found out in cultivars W 43 and Super Queen (in both of them the average duration of microsporogenesis was 106 days. In the control cultivar Redhaven the average length of the period of microsporogenesis was 104 days. In individual cultivars, the course of microsporogenesis was different and was dependent on meteorological conditions existing in individual years.

Disturbances in microsporogenesis and pollen grain development in Gagea lutea (L.) Ker. Gaw.

The meiotic division of microsporocytes and pollen grain development in <i>Gagea lutea</i> (L.) Ker.-Gaw. (Liliaceae) with fluorescence microscope (excitation light 400 nm) was observed after squashing the anthers in DAPI solution (fluorochrom dying DNA). Up to 70% of microsporocytes and pollen grains during the microsporogenesis and pollen grain development take a regular course. In the remaining microsporocytes and pollen grains (30%) the disturbances in course of both processes were observed. The most often observed disturbances are "late" chromosomes and a presence of micronuclei. The divisions of microsporocytes in the anther loculi show a big asynchrony, which, like the disturbances during the course of microsporogenesis and pollen grain development, may be caused by the external factors. The microsporogenesis takes place during autumn and winter months: the pollen grains develop in winter. At this time the dividing microsporocytes and developing pollen grains are under the influence of abiotic factors as low temperature and a lack of water. These factors disturb the formation of microtubular cytoskeleton of the dividing microsporocytes and pollen grains, which causes the formation of sterile pollen grains.

Meiosis and pollen formation in haploid Thuja plicata gracilis Oud.

Male strobili development and the course of microsporogenesis were studied on a tree growing in the Botanical Garden at Stockholm as well as on cuttings from a haploid and a diploid plant of Thuja plicata. The plants from cuttings were kept in a phytotron experiment at different photoperiods and treated with gibberellin in order to get rich flowering. The development of the strobili and the course of microsporogenesis were very variable under different ecological conditions. The best result (similar to that of the tree in Botanical Garden) was obtained when the plants from cuttings were kept for 17 weeks in long day during which period the plants were sprayed with gibberellin, twice a week. A rich initiation of buds was obtained but the development remained arrested at this initiation stage (corresponding to preprophase-pachytene). After transferring the plants to short day the strobili development and microsporogenesis continued and were completed after 14 weeks. Thus, the photoperiodical sequence necessary for complete development of pollen grains was long day — short day. The pollen grains in diploid plants were normally developed but those in haploid ones showed irregularities caused by meiotic disturbances.

In vitro protein synthesis in isolated microspores of Zea mays at several stages of development

A new procedure has been used providing large and homogenous populations of pollen from maize at different stages of their development. In order to label proteins synthesized during the course of microsporogenesis, a method has been developed that allows an efficient uptake of amino acids in the microspores. Results are presented showing that during pollen development three specific steps are involved: an early period active in protein synthesis, followed by a rest period when starch is accumulated, and a third period preceding the sorting out of mature pollen grains and during which protein synthesis starts again at a relatively low level. New polypeptides, some of which are very basic, appear at the time of starch deposition and accumulate up to the mature stage.

Changes in intracellular localization of peroxidase during Microsporogenesis in Gymnosperms

Cytochemical investigations on peroxidase localization during microsporogenesis inLarix europaea D.C.,Taxus baccata L. andPinus sylvestris L. have revealed striking differences in the localization and activity level of this enzyme linked with the developmental stage.The localization and level of activity of peroxidase, typical of each stage, changed in the course of microsporogenesis in a strictly orderly way, giving a characteristic and stable pattern. The pattern of intracellular peroxidase localization proved to be the same for microsporogenesis of all the gymnosperms in question.It is suggested that the identity of that pattern in plants so phylogenetically distant asTaxus baccata L. andPinus sylvestris L. indicates that peroxidase activity in gymnosperms’ microsporogenesis is connected with the fundamental and genetically well stabilized processes of meiotic cytodifferentiation.Moreover, enhanced peroxidase activity has been found in the sites of callose walls synthesis of dyads and tetrads, which suggests the participation of this enzyme in callose synthesis.

A case of early dissolution of the microsporocyte callose wall in male-sterile (CMS) sweet pepper (Capsicum annuum L.)

On squash preparations of anthers from pollen fertile and sterile plants of sweet pepper (Capsicum annuum L. cv. Severka) callose envelopes of microsporocytes, stained specifically with resorcin blue, were investigated microscopically. During normal course of microsporogenesis in fertile plants the envelopes remained intact up to the stage of microspore tetrads. Then callose begins to dissolve, and that from individual microspores towards the envelope periphery. In sterile analogues of the same cultivar the callose breakdown occurred precociously, usually in the course of the second, but sometimes as early as the first meiotic division of PMCs. Having completed meiosis sporadic microsporocytes formed microspore tetrads. Most PMCs contained an undivided four-nucleate protoplast rimmed with a narrow or wider unstained zone of dissolved callose. In certain cases more condensed callose septa pointing to the furrows on the surface of the PMC protoplast were well-observable in this lytic zone, as a residuum of normal mechanism of tetradogenesis.

In vivo embryoids from anthers of Narcissus biflorus Curt

Mature anthers of some plants of Narcissus biflorusCuri., cultivated under subtropical conditions at Jammu, were found to contain monads, microspore mother cell embryo sacs, and multinucleate ‘embryoids’. In addition, multicellular ‘embryoids’ resembling those obtained in vitro through anther culture were also observed. All these structures arise from the microspore mother cells which do not follow regular course of microsporogenesis.

The effect of gametocides on microsporogenesis of winter rye

The effect of gametocides FW-450, maleic hydrazide and Dalapone on the course of microsporogenesis, gametogenesis and starch synthesis in pollen grains of winter rye ev. ‘Esto’ was investigated. Solutions containing various concentrations of tested substances were applied on leaves in amount of 2.5 ml and 5.0 ml per plant at the beginning, at the full and at the end of shooting. The effect of gametocides was detectable already in the phase of microspore formation when a decrease of anther weight, pollen grain size and starch content in grains and an increase of the number of microspores with nonfinished development were observed. The manner and the extent of injuries were dependent on the applied substance, its concentration and on period of its application.

Synaptonemal-like complexes in Allium cepa Microspores

The paper describes the synaptonemal-like complexes found in the course of microsporogenesis in Allium cepa, during the young microspore stage. In longitudinal sections these structures are morphologically more or less like the synaptonemal complexes, which appear during the pachytene stage of meiosis, and consist of two regions resembling the lateral elements, separated from one another by a space measuring about 1000 A, in which a central element is occasionally observed. When observed in transverse or oblique sections, their shape indicates that they are tubular structures with a central axis; they are generally observed as independent units inside the nucleus, sometimes associated with the chromatin masses.

CYTOLOGICAL AND MORPHOLOGICAL STUDIES OF DIPLOID AND TETRAPLOID SPECIES OF <i>IPOMOEA BILOBA</i>

A detailed comparative cytomorphic study of the diploid Ipomoea biloba Forsk. (2n=30) and a naturally-occurring tetraploid form (2n=60) was made. The extent of morphological differences between the two chromosomal types have been presented and discussed. These differences relate to leaf shape and size, pollen size and length of seed coat hair. The course of microsporogenesis was investigated from pachytene stage onwards in both the taxa. Based on these data and their geographical distribution, the mode of origin of the tetraploid taxon and its relationship to the diploid was considered. The close similarity in their exomorphic characters, presence of both the diploid nucleolar chromosomal types in tetraploid and the sympatric distribution of the two taxa are advanced as evidences in favour of the direct role played by diploid biloba in the origin of the tetraploid taxon. However, in view of the prevalence of preferential pairing, low multivalent frequency and high fertility, a segmental allopolyploid origin seems probable.

Microsporogenesis in <i>Manihot esculenta</i>

Microsporogenesis was investigated in selected cultivars of Manihot esculenta being cultivated at the Instituto Interamericano de Ciencias Agricolas in Turrialba, Costa Rica. The course of microsporogenesis was found to be “normal” in these cultivars and various stages of the process were recorded.

The Climatic Influences upon the Pollen Development of the Italian Hemp

1. The microsporogenesis of the Italian hemp, grown up under Moscow and Caucasia conditions has been investigated. 2. The Italian hemp cultivated in Caucasia had with a very few exceptions, a quite normal course of pollen development. 3. The same hemp grown up in Moscow district showed a large number of different irregularities during the microsporogenesis. The most striking of them were: fusion of the nuclei in the archesporial tissue, in prophases and in the first and second telophases, failure of conjugation of chromosomes, formation of the restitution-nuclei in the first and second divisions etc. 4. The young pollen grains of the Italian hemp in Caucasia had regular round forms and a small coefficient of variation in size. 5. The young pollen of the Italian hemp in Moscow district had a great number of deformed, gigantic, dwarfish, polynuclear etc. grains. 6. As all the conditions, except the climatic ones, were the same in the both cases, we find that such a difference in the course of microsporogenesis may only be attributed to climatic influences.

The climatic influences upon the pollen development of the Italian hemp

1. The microsporogenesis of the Italian hemp, grown up under Moscow and Caucasia conditions has been investigated. 2. The Italian hemp cultivated in Caucasia had with a very few exceptions, a quite normal course of pollen development. 3. The same hemp grown up in Moscow district showed a large number of different irregularities during the microsporogenesis. The most striking of them were: fusion of the nuclei in the archesporial tissue, in prophases and in the first and second telophases, failure of conjugation of chromosomes, formation of the restitution-nuclei in the first and second divisions etc. 4. The young pollen grains of the Italian hemp in Caucasia had regular round forms and a small coefficient of variation in size. 5. The young pollen of the Italian hemp in Moscow district had a great number of deformed, gigantic, dwarfish, polynuclear etc. grains. 6. As all the conditions, except the climatic ones, were the same in the both cases, we find that such a difference in the course of microsporogenesis may only be attributed to climatic influences.