Aggregations of organelles in meiotic cells of higher plants

During early prophase I in microsporocytes and sporocytes of various plants all mitochondria and plastids aggregate in a group, where some plastids seem to undergo division. This group desintegrates by middle prophase I. Further aggregations of plastids and mitochondria occur in microsporogenesis and sporogenesis is of a simultaneous type. Organelles aggregate the second time at the end of prophase 1 and during or after telophase I they form a dense equatorial plate which lasts until telophase IL Since the phragmoplast is dismantled after telophase I and there is no cytokinesis, organelles aggregated in the plate apparently prevent merging of the nuclei and spindles of meiosis II, thus taking over a role of a phragmoplast and cell wall. In some plants after telophase II organelle aggregation changes shape and occupies the planes where cell walls will be built in simultaneous cytokinesis. Positioning of plastids and mitochondria along these planes may facilitate their equal apportionment among the postmeiotic cells.

Patterns of amyloplast distribution during microsporogenesis in Tradescantia, Impatiens and Larix

During the meiotic prophase I in <em>Tradescantia</em> and <em>Impatiens</em> microsporocyte becomes temporarily asymmetric, with excentrically situated nucleus and all amyloplasts gathered in a dense group close to the nuclear envelope.. Further microsporogenesis in <em>Impatiens</em> differs in amyloplast distribution from that in <em>Tradescantia</em> and <em>Larix</em>. In Impatiens at the telophase I amyloplasts are assembled in a dense equatorial plate. At the late telophase II this plate reshapes and separates a meiocyte into four areas (a tetrad) until cell plates are formed in simultaneous cytokinesis. Similar assemblages of amyloplasts do not occur in telophase meiocytes of <em>Tradescantia</em> and <em>Larix</em> where cytokinesis is of a successive type.

Artificial drainage devices for glaucoma surgery: an overview

Artificial drainage devices (ADD) create an alternative pathway for aqueous drainage from the anterior chamber of an eye through a tube to the subconjunctival bleb connected to an equatorial plate under the conjunctiva. The ADDs, both valved and non-valved, are available for end stage or refractory glaucoma. Currently, some of these devices, particularly the Express shunt, are recommended for the primary treatment of glaucoma. In this article, we highlight various ADDs, their indications and contraindications, surgical techniques and associated complications.DOI: http://dx.doi.org/10.3126/nepjoph.v4i2.6547 Nepal J Ophthalmol 2012; 4 (2): 295-302

Cytological evidence for assortment mitosis leading to loss of heterozygosity in rice

In the root meristem cells of the rice line AMR, which causes loss of heterozygosity in its hybrids, both normal and assortment mitoses were observed. During normal mitosis, chromosomes did not form homologous pairs at metaphase; all chromosomes lined up at the equatorial plate and 2 chromatids of each chromosome disjoined at the centromere and moved toward opposite poles. During assortment mitosis, varying numbers of paired homologues were observed at mitotic metaphase. Two groups of 12 chromosomes separated and moved towards the opposite poles of daughter cells with few chromosomes having their chromatids separated at anaphase. These observations support the proposed mechanism that is responsible for early genotype fixation in rice hybrids involving AMR.Key words: mitosis, homologous chromosome, genotype fixation, loss of heterozygosity, rice.

Mechanisms and inheritance of first division restitution in hybrids of wheat, rye, and Aegilops squarrosa

First division restitution (FDR) in intergeneric Triticeae hybrids provides an important meiotic mechanism for the production of amphidiploids without the use of colchicine and similar chemicals. The genetic controls of FDR were investigated by examining microsporogenesis and fertility in F1 hybrids of two- and three-way crosses of durum wheat (Triticum turgidum L. var. durum) cultivars Langdon (LDN) and Golden Ball (GB), 'Gazelle' rye (Secale cereale L.), and one accession (RL5286) of Aegilops squarrosa L. The results from two-way crosses indicated that the first meiotic division varied, depending on the hybrid. GB crossed with Ae. squarrosa developed tripolar spindles and prevented congregation of chromosomes at the equatorial plate. The hybrid of GB with rye had a delayed first division. But, the hybrids of LDN with both Ae. squarrosa and rye had a high frequency of FDR. Analysis from the three-way crosses indicated that inheritance in rye crosses differed from those with Ae. squarrosa. FDR segregated in a 1:1 ratio in the rye cross, suggesting that the FDR is controlled by a single gene from LDN. However, FDR fit a 1:3 ratio in the three-way crosses with Ae. squarrosa. Cytological data suggested that tripolar spindles are a major factor preventing FDR in Ae. squarrosa crosses. Some progenies from the three-way cross with rye had a high frequency of monads that resulted from second division failure of FDR cells.Key words: durum wheat, rye, Aegilops squarrosa, first division restitution, tripolar spindle.

Human acrosome biogenesis: immunodetection of proacrosin in primary spermatocytes and of its partitioning pattern during meiosis

Proacrosin biosynthesis timing during human spermatogenesis has been studied using the monoclonal antibody 4D4 (mAb 4D4). Frozen and paraffin-embedded sections of testicular biopsies were labelled by standard indirect immunofluorescence and avidin-biotin immunoperoxidase procedures. The labelling specificity was checked by immunochemistry assays on unrelated tissues and by western blotting of testis extracts showing that only the 50–55 × 10(3) Mr proacrosin was recognized by mAb 4D4. Proacrosin was first observed in the Golgi region of midpachytene primary spermatocytes. In late pachytene primary spermatocytes, proacrosin was observed in two regions located at opposite nuclear poles. During the subsequent steps of the first meiotic division, the two bodies containing proacrosin were located: (i) on opposite sides of the equatorial plate during metaphase; (ii) along the microtubular spindle during anaphase; and (iii) close to each chromosomal aggregate during telophase. Two bodies containing proacrosin were still observed in interphasic secondary spermatocytes. The single labelled area observed in early spermatids was found to increase considerably in size during spermiogenesis. Anomalies of proacrosin scattering were observed in patients with Golgi complex partitioning failure. These data reveal proacrosin biosynthesis during diploid and haploid phases of human spermatogenesis and the proacrosin partitioning pattern during meiosis.

Microtubule polarity in taxol-treated isolated spindles

Spindles were isolated from Spisula oocytes in the presence or absence of taxol to determine if cell lysis procedures previously used to analyze spindle microtubule polarity may have resulted in the loss of any microtubules of a particular polarity. Electrophoretic analysis indicated that spindle preparations isolated in the presence of taxol contained considerably more tubulin than did those isolated in the absence of taxol. Although there was no corresponding increase in the birefringence of the taxol-treated isolated spindles, thereby suggesting that they did not possess a greater concentration of aligned microtubules between the poles and the equatorial plate, electron microscopy revealed that the taxol-treated isolated spindles did, in fact, contain more microtubules than did the nontaxol-treated isolated spindles. These microtubules were predominantly localized immediately around the centrioles, suggesting that assembly may have occurred during the lysis into taxol. The spindles were decorated with Chlamydomonas dynein to display microtubule polarity. The majority of microtubules, located between the chromosomes and poles, possessed a uniform polarity in both taxol- and nontaxol-treated isolated spindles. In the region of the chomosomes, however, up to 45% of the microtubules were oriented with a polarity opposite to the remainder and were intermingled among them. It is probable that microtubules with opposite polarities arise from the opposing poles and overlap in the equatorial region. The extent of overlap appears to be quite substantial and thus may be of significance during mitotic movements.

Ultrastructure of Persisting Mitotic Nucleoli of Mung Beans

Although nucleoli are generally believed to disperse during mitotic prophase, various groups of algae, fungi, and protozoans regularly possess persisting, in some cases “autonomous,” nucleoli during mitosis. Persisting nucleoli also occur in some higher plants and animals, but there have been only a few ultrastructural observations of such nucleoli. This study was initiated to better characterize cell divisions of a plant in which nucleoli regularly persist during mitosis.Aceto-carmine squash preparations for staining nucleoli for light microscopy reveal that mung bean primary roots possess mitotic divisions in which over 90% of the metaphases exhibit nucleoli. One micrometer sections of plastic embedded tissue stained with aqueous methylene blue for light microscopy also show nucleoli at metaphase (Fig. 1). Light microscopic observations show that some metaphase nucleoli are roughly spherical and occur on or near the equatorial plate; some are elongated perpendicularly to the plane of the equatorial plate and extend toward one or the other, or both, pole(s); while others appear spherical and occur at either pole.