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We have developed an experimental system in which the irradiation with a red light pulse induces stomatal disorientation in the hypocotyl epidermis ofCucumis sativus L. In this system, the orientation of the division plane in guard mother cells was not defined correctly. Preprophase bands formed in these cells but their orientation was abnormal.

In a comparison of cambial cells and their derivatives between naturally occurring dwarf and normal trees, vessel elements and fibers in the annual rings of dwarf trees were found to be shorter, narrower and fewer than those of normal trees. The frequency of anticlinal divisions and loss of cambial initials were low during the differentiation of xylem cells from cambial initials in dwarf trees. The length and intrusive growth of fusiform initials were slightly less than those of normal trees. Thus, it was concluded that the shortening of vessel elements and fibers in dwarf trees was due to the fact that cambial initials were themselves shortened and underwent inactive intrusive growth during differentiation of the xylem mother cells.

Budding yeast cells divide asymmetrically, giving rise to a mother and its daughter. Mother cells have a limited division potential, called their lifespan, which ends in proliferation-arrest and lysis. In this report we mutate telomerase in Saccharomyces cerevisiae to shorten telomeres and show that, rather than shortening lifespan, this leads to a significant extension in lifespan. This extension requires the product of the SIR3 gene, an essential component of the silencing machinery which binds to telomeres. In contrast, longer telomeres in a genotypically wild-type strain lead to a decrease in lifespan. These findings suggest that the length of telomeres dictates the lifespan by regulating the amount of the silencing machinery available to nontelomeric locations in the yeast genome.

From a comparison of cambial cells and their derivatives between naturally occurring dwarf trees and normal ones, it was concluded that tracheids in the annual rings of dwarf trees are shorter, narrower and fewer than those of normal trees. The frequency of anticlinal division and loss of cambial initials is low during differentiation of xylem cells from cambial initials in dwarf pines. The length and intrusive growth of fusiform initials are slightly less than those of normal trees. Thus, it is concluded that the shortening of tracheids in dwarf trees is due to the fact that cambial initials are themselves shortened and that intrusive growth during differentiation of xylem mother cells has occurred.

Two kinds of poles, the PP and the MP, are manifested just prior to and during the synaptic stage of meiosis in the SMCs of Equisetum. A spectroscopic and ultracytochemical characterization of these poles has been carried out to elucidate their functions. The former pole not only works as the intracellular center of carbohydrate metabolism in this stage, but also as a possible supply center of intermediates for protein and fat biosyntheses. In contrast, the latter pole functions as the intracellular center of ATP production in this stage. This synaptic pole formation is causally related to the “chromosome and molecular pairing” of meiosis.

Ultrastructural analysis of B chromosome synapsis in surface-spread (2B) pollen mother cells of the leek, Allium porrum, has clarified their structural organization and shed new light on their origin. In pachytene cells containing two B chromosomes, these chromosomes either formed a pair of univalents showing foldback hairpin loops or synapsed together to form bivalents of several different types. The synaptic configurations of univalents and bivalents indicate that these B chromosomes have a basically isochromosome organization, but this is modified by a slight centric shift giving an arm ratio of 1.1:1. This analysis adds to the growing number of B chromosomes that have been shown to be isochromosomes or isochromosome derivatives. Key words : Allium porrum, B chromosomes, synapsis, synaptonemal complex, isochromosome.

SUMMARYThe present study was aimed to assess the impact of air pollutants from the Kerala Minerals and Metals Ltd. on meiosis in Datura metel L. growing at different sites around the factory. Cytological studies in the pollen mother cells revealed the presence of chromosome breakages, chromosomal interchanges and spindle abnormalities.

International audience; We designed a microfluidic chemostat consisting of 600 sub-micron trapping/growth channels connected to two feeding channels. The microchemostat traps E. coli cells and forces them to grow in lines for over 50 generations. Excess cells, including the mother cells captured at the start of the process, are removed from both ends of the growth channels by the media flow. With the aid of time-lapse microscopy, we have monitored dynamic properties such as growth rate and GFP expression at the single-cell level for many generations while maintaining a population of bacteria of similar age. We also use the microchemostat to show how the population responds to dynamic changes in the environment. Since more than 100 individual bacterial cells are aligned and immobilized in a single field of view, the microchemostat is an ideal platform for high-throughput intracellular measurements. We demonstrate this capability by tracking with sub-diffraction resolution the movements of fluorescently tagged loci in more than one thousand cells on a single device. The device yields results comparable to conventional agar microscopy experiments with substantial increases in throughput and ease of analysis.

Over the past 15 years, the number of papers published on sirtuins has exploded. The initial link between sirtuins and aging comes from studies in yeast, in which it was shown that the life span of yeast mother cells (replicative aging) was proportional to the SIR2 gene dosage. Subsequent studies have shown that SIR2 homologs also slow aging in C. elegans, Drosophila, and mice. An important insight into the function of sirtuins came from the finding that yeast Sir2p and mammalian SIRT1 are NAD(+)-dependent protein deacetylases. In mammals, there are seven sirtuins (SIRT1-7). Their functions do not appear to be redundant, in part because three are primarily nuclear (SIRT1, 6, and 7), three are mitochondrial (SIRT3, 4, and 5), and one is cytoplasmic (SIRT2). The past decade has provided an avalanche of data showing deacetylation of many key transcription factors. In this chapter, I will address the evidence that sirtuins mediate the effects of CR on physiology and will then turn to the evidence of a relationship between sirtuins and aging and life span. Finally, I will discuss the roles of sirtuins in diseases of aging and the prospects of translating these findings to novel therapeutic strategies to treat major diseases.

SUMMARYMeiotic studies in the pollen mother cells and embryo-sac mother cells were undertaken in Brassica oxyrrhina Coss. which carry several agronomically important traits. Unlike the earlier reports suggesting higher chiasma frequency on the female side, presently higher chiasma frequency was observed in the male sex cells. It is concluded that the chiasma formation in the two sex cells is regulated by different controlling systems of genes.

Cytomixis, representing the migration of chromatic material from one cell to another, was observed in PMC's of Polygonum tomentosum Schrank. Cytomixis was observed at all stages of meiosis, but became less frequent in the later stages of meiosis. Direct nuclear fusion and cytoplasmic connections between cells were noted, so that a series of PMC's were sometimes connected togther.Cytomictic cells were often accompined by other meiotic aberrations such as univalents, laggard and disoriented chromosomes. Levels of pollen stainability are low, indicating a high of male sterility in these populations.

SUMMARYThis study was carried out in Devon, UK, using Apis mellifera colonies that were naturally infested with Varroa jacobsoni. Study frames with uniform areas of similarly aged sealed brood were used in order to reduce the possibility of fluctuations in infestation rate occurring. Cells were examined at regular intervals and their contents (mother mites and offspring at different stages of development, alive or dead) were determined. A total of 908 worker cells containing 1334 mother mites and 2671 drone cells containing 3455 mother cells were found in the 3228 worker cells and 16 252 drone cells examined. The number of cells containing different numbers of mother mites did not differ significantly from a random (Poisson) distribution, irrespective of brood type (drone or worker), at any constant infestation level. The maximum number of viable adult offspring (male and female) observed in a single drone or worker cell was 16 and eight respectively. The mean number of eggs laid per mite in both drone an...

Initial vascular differentiation is generally considered to occur in procambium. In ferns, however, a provascular tissue immediately subjacent to the promeristem has been suggested as an initial stage within which the procambium is subsequently formed. In contrast to this interpretation, a zonation concept applied in ferns recognizes a promeristem consisting of several layers of cells in which no differentiation takes place. This study demonstrates that the shoot apex of Matteuccia struthiopteris has one cell layer of promeristem. Immediately subjacent to the promeristem is the provascular tissue surrounding a central group of pith mother cells. The developmental continuity between the provascular tissue and the mature vascular tissue, and between the pith mother cells and the pith, through transitional stages, indicates that the initial differentiation of vascular tissue and pith takes place in this prestelar tissue. The continuity of vascular differentiation in the area confronting young leaves or incipient leaf positions is interrupted by the formation of leaf gap initials. Developing leaves thus begin to exert influence on the vascular system at the prestelar stage. Small protoxylem elements with helical cell wall thickening, and distinctive protophloem elements are present in the leaf traces, but end abruptly near the junction regions of leaf traces to the meristele.

The yeast Saccharomyces cerevisiae typically divides asymmetrically to give a large mother cell and a smaller daughter cell. As mother cells become old, they enlarge and produce daughter cells that are larger than daughters derived from young mother cells. We found that occasional daughter cells were indistinguishable in size from their mothers, giving rise to a symmetric division. The frequency of symmetric divisions became greater as mother cells aged and reached a maximum occurrence of 30% in mothers undergoing their last cell division. Symmetric divisions occurred similarly in rad9 and ste12 mutants. Strikingly, daughters from old mothers, whether they arose from symmetric divisions or not, displayed reduced life spans relative to daughters from young mothers. Because daughters from old mothers were larger than daughters from young mothers, we investigated whether an increased size per se shortened life span and found that it did not. These findings are consistent with a model for aging that invokes a senescence substance which accumulates in old mother cells and is inherited by their daughters.

Protein damage segregates asymmetrically in dividing yeast cells, rejuvenating daughters at the expense of mother cells. Zhou et al. now show that newly synthesized proteins are particularly prone to aggregation and describe a mechanism that tethers aggregated proteins to mitochondria. This association constrains aggregate mobility, effectively retaining and sorting toxic aggregates away from younger cells.

In Saccharomyces cerevisiae, the bud site selection of diploid cells is regulated by at least four persistent landmarks, Bud8p, Bud9p, Rax1p, and Rax2p. Bud8p and Bud9p are essential for the establishment of bipolar budding and localize mainly to the distal and the proximal poles, respectively. Their subcellular localizations are regulated through interaction with Rax1p/Rax2p. We investigated when and where Bud8p and Bud9p physically interact with Rax2p in vivo using a split-GFP method. GFP fluorescence showed that Bud8p physically interacted with Rax2p at the proximal or distal pole in unbudded cells; a physical interaction was also observed at the opposite pole to the growing bud in mother cells with a large-size bud. Bud9p physically interacted with Rax2p at the birth scar in budded mother cells. These observations suggest that the interaction of Rax2p with Bud8p and Bud9p may contribute to the translocation of bipolar landmarks to the correct sites.

We propose a hypothetic mechanism of ordering and shaping cells during C. elegans embryogenesis. The mechanism is based on the assumption that during each round of division of cells, daughter cells acquire electric charges from its mother cells (charge conservation law is taken into account). Between the acts of division, the total electric field, generated by a system of charged cells, change relative positions of the charged cells within the region. In one’s turn, the positions of the charged cells determine the pattern of the electrostatic field. A mathematical model of such self-consistent mechanism is developed. The process of developing the sixteen-cell structure starting with one cell is simulated. The results correspond to the known experimental data.

We have shown that the red cells found in the Red Rain (which fell on Kerala, India, in 2001) survive and grow after incubation for periods of up to two hours at 121 oC . Under these conditions daughter cells appear within the original mother cells and the number of cells in the samples increases with length of exposure to 121 oC. No such increase in cells occurs at room temperature, suggesting that the increase in daughter cells is brought about by exposure of the Red Rain cells to high temperatures. This is an independent confirmation of results reported earlier by two of the present authors, claiming that the cells can replicate under high pressure at temperatures up to 300 oC. The flourescence behaviour of the red cells is shown to be in remarkable correspondence with the extended red emission observed in the Red Rectangle planetary nebula and other galactic and extragalactic dust clouds, suggesting, though not proving, an extraterrestrial origin., Comment: 11 pages 10 figures SPIE Conference 7819 Instruments, Methods, and Missions for Astrobiology XIII Aug. 3-5 2010 San Diego, Ed. Richard B. Hoover

Summary A second find of Tetrasporopsis fuscescens in Austria and a fifth altogether is reported. From four finds one can conclude that this species requires cool and slow- or moderately fast-flowing water. In raw culture, reproduction of cells for limited time, but no normal organization of thalli could be achieved. Characteristic details of thallus structure as well as morphology and development of cells are stressed. Repeated observation of stigmata throughout the year in a number of cells and of emptied cells in large fields indicates the capacity to produce zoospores. Release of thin-walled stigmaless cells from their mother cells occurs sporadically; whether they get free from thalli remains open. Conspicuous changes induced by winterly conditions throw some light on normal developmental processes. - The alga gathered in 1853 is not Braun's but De Baby's collection. It is a green alga and not, as thought by some authors, T. fuscescens .

In pollen mother cells of triploid Petunia axillaris (Lam.) B. S. P. at the stage of late diakinesis some of the chain trivalents revealed an unusual form of rigidity. These are here described as “hook-shaped”, although earlier documented as ‘L’ shaped chain trivalents (Reddi and Padmaja 1979). The other point considered was whether a similar form of rigidity is also true for some rod bivalents, where the single chiasma was terminalized. Such“ paranormal bivalents” were in fact observed. The corresponding observation of hook-shaped trivalents at late diakinesis is interpreted to be a factor that could limit the frequency of alternate orientation and incidentally increase the frequency of adjacent orientation of such chains at metaphase I.

The paper considers a number of abnormal phenotypes with impaired temporal regulation of cytokinesis during the meiotic division of pollen mother cells. The phenomenon of “non-stop” cytokinesis with blocked arrest of the phragmoplast centrifugal motion and cell plate growth as well as incomplete and premature cytokinesis are described. The obtained data suggested a model for regulation of the processes involved in the arrest of the main cytokinesis processes during its completion in the plant meiosis.

A diminutive species of Aglaothamnion (Ceramiaceae, Rhodophyta), A. diaphanum sp. nov., is described from Brittany (Atlantic France), the Isles of Scilly (off S.W. England) and western Ireland. Aglaothamnion diaphanum is confined to the sublittoral zone, where it grows almost exclusively on algae and sessile animals attached to hard substrata. Thalli are delicate, and branched distichously in one plane. The main axes are ecorticate but may form loose non-corticating rhizoidal filaments. The lateral branches bear a characteristic, regularly alternate distichous series of branchlets, the first of which is always adaxial. All vegetative cells are uninucleate. The majority of field-collected plants bear only bisporangia, but a few bisporangial plants also form spermatangia; some male plants and a single female specimen have been collected. The spermatangial branchlets consist of 3–5 spermatangial mother cells each bearing 2–4 spermatangia, which are constricted around a central nucleus. None of the U...

Treatment ofZea mays seedlings with a 5 mM caffeine solution inhibits cytokinesis in guard cell mother cells (GMCs), producing unicellular, binucleate aberrant stomata (a-stomata). Ventral wall (VW) strips of limited length, which usually meet the wall portions of GMCs adjoining the cortical zone of the preprophase microtubule band (PMB), are laid down in many a-stomata.

Chytridiopsis typographi Weiser, 1954, the microsporidian pathogen of the spruce bark beetle, Ips typographus L. (Coleoptera: Scolytidae), has an early developmental period with plurinucleate mother cells, each of which produces a single bud. The globular bud is connected with the mother cell by a collar and the cellular constituents are pushed to the distant end of the bud. Both the mother cell and the bud continue to develop; the bud then separates from the mother cell and grows to produce a cell of the same type. Both cells then continue sporogonial development and produce sporophorous vesicles with 16-32 spores. The process of a single mother cell producing a single bud that grows to an identical stage is new in the development of C. typographi and has no analogy in other Microsporidia.

Reproductive apparatus of Gracilaria/Gracilariopsis lemaneiformis collected from Qingdao city were studied with a light and a transmission electron microscope. The special superficial arrangement of spermatangium for this species was clearly observed, and the ultrastructure of spermatangial development revealed the similar cytodynamic pattern followed by all the Gracilariaceae members developed from spermatangial mother cells to spermatangium. The female reproductive apparatus before fertilization was also observed and trichogyne was found protruding above the cortex, contrary to the earlier reports. Tetrasporangium was formed by an outer cortical cell and the tetraspores became spherical and expended after being released.

Pollen mother cells of the lily (Lilium speciosum) were found to have a histone-H1-like protein (PMCP) not detected in other tissues. The PMCP appears from the late S-G(2) period of premeiosis and is present in mature pollen. PMCP and H1 were extracted from pollen mother cells with 5% perchloric acid and isolated by reverse-phase high-performance liquid chromatography. The amino acid composition of PMCP differs from that of somatic H1. However, PMCP is similar to H1t in mammalian testis with regard to amino acid composition.

Zusammenfassung Die Salzdrusen der Gattung Limonium leiten sich ontogenetisch von einer einzelnen epidermalen Zelle ab, die sich in funf Teilungsschritten zu einem 20-zelligen Drusenkomplex differenziert. Die Cutinisierung des Drusenkomplexes erfolgt bereits nach dem vierten Teilungsschritt bei der Bildung der vier Sammel- und der vier Bechermutterzellen. Diese werden durch den funften Teilungsschritt in innere und ausere Becherzellen geteilt. Abstract The Limonium-salt gland develops from only one epidermal cell in five steps of cell-division to a gland complex of 20 cells. Cutinisation on the gland complex starts after the fourth step of cell-division, when four collecting cells and four mother cells of the cup cells are formed. In the last step the mother cup cells divide into four inner cup cells and four outer cup cells.

Cytomixis has been observed for the first time in a tetraploid Alopecurus arundinaceus (2n=4x=28). This phenomenon has resulted in the formation of hypo- and hyperploid cells which, however, failed to reach later stages of meiosis.

The whole position in L. nivea can be summed up as follows. In the control material, parts of the otherwise normal inflorescence contained asynaptic pollen mother cells; the implication being that the asynapsis was due to a mutant gene, present in a sector of the inflorescence. In the irradiated material, in the M1 generation, in accordance with expectation that the plants will be chimaeras, buds are found on the same plant which may be normal, or asynaptic, or produce diplobivalents, or in which the daughter nuclei degenerate following meiosis.

Realizou-se o estudo do comportamento meiótico de C. canephora tetraplóide com 2n =44 cromossomos por tratar-se de uma espécie considerada possível ancestral de C. arabica (2n = 44): constatou-se, em 92,0% das células-mães de pólen, em todas as fases da microsporogênese estudada, 2n = 44 cromossomos. Em diacinese os cromossomos se apresentaram na forma de mono-, bi-, tri- e tetravalentes. Em metáfase 1, somente 13,16% das células apresentaram 22II sendo a seguinte a fórmula média do pareamento: 3,61I; 15,21II 0,71III e 1,93IV. As irregularidades anafásicas resumiram-se praticamente na disjunção desigual dos cromossomos para os pólos de 21-23, 20-24 e 19-25. Somente 37,65% das células apresentaram segregação normal de 22 cromossomos para cada pólo. Em anáfase II, observaram-se sete tipos diferentes de distribuição cromatídica e, também, somente em 26,0% das células foi encontrada distribuição normal dos cromossomos. Após a citocinese, foram observadas tríades (1,6%), tétrades (77,0%) e políades (21,4%). A inviabilidade dos grãos de pólen foi alta, 79,0%. Observações em cortes transversais medianos de frutos mostraram 43,4% do tipo normal, sendo 11,0% do tipo moca e 32,4% do chato. Em 56,6% dos frutos, não houve desenvolvimento de sementes, formando-se apenas perisperma.

We applied environmental stresses, namely dehydration, pruning and bending, to woody taproots of Fraxinus ornus L. in order to: (i) identify a method that could be applied in routine studies of lateral root development from a secondary structure; and (ii) carry out anatomical investigations to identify the tissue involved in the recruitment of lateral root mother cells (LRMC). We found that all three methods induce the formation of new lateral roots from a woody parental root. However, bending stress considerably reduced the zone of the woody parental root (the curvature) for analysis when studying the process of emission of a new lateral root. The trace left by a new lateral root in the taproot secondary xylem forms a V-shaped insertion zone that starts in contact with a growth ring and enlarges toward the periphery. This type of insertion zone suggests that the vascular cambium is the tissue-source of initials that produce the root primordium of a new lateral root. In the case of root bending, ...

I have a long-term interest in protein homeostasis in single cell organisms including E. coli and S. cerevisiae . Developments in my laboratory lead to the discovery that damaged proteins are inherited in a non-Mendelian, asymmetrical, fashion in budding yeast such that most damaged proteins are retained in old mother cells, which will allow for rejuvenation of the progeny (Aguilaniu et al. 2003; Erjavec et al. 2007; Liu et al. 2010). This discovery highlighted that protein quality control entails spatial control and provided the impetus for my and other labs to elucidate the mechanism by which organisms sequester and harness cellular damage (Liu et al. 2010; Liu et al. 2011; Malmgren Hill et al. 2014). For this research I have received the Goran Gustavsson Award in Molecular Biology from the Royal Swedish Academy of Sciences and a Wallenberg Scholar Award from the Wallenberg Foundation. > Q:You have recently received a prestigious award for your work on yeast. Can you tell us more about that? > > I was awarded the Emil Christian Hansen Gold Medal 2015 for “groundbreaking studies on …

Copyright © 2006 International Phycological Society. Specimens from the eastern Atlantic, Mediterranean and Adriatic seas previously reported as Botryocladia chiajeana showed differences in morphology, and re-examination of Meneghini's original collection of Chrysymenia chiajeana (basionym B. chiajeana) revealed that only the Mediterranean and Adriatic specimens are in agreement with the original protologue, whereas plants reported from the eastern Atlantic are recognised here as Botryocladia macaronesica Afonso-Carrillo, Sobrino, Tittley & Neto sp. nov. The vegetative and reproductive morphology of western Mediterranean plants is examined in detail for the first time, and B. chiajeana is characterised by the following combination of features: solid axes bearing frequently dichotomously branched vesicles, vesicle walls three layered, outer cortical cells arranged in rosettes, secretory cells borne on modified medullary cells, spermatangia cut off from scattered spermatangial mother cells, cystocarps strongly protuberant and tetrasporangia cruciately divided and exposed on the outer cortical layer at maturity. From the Meneghini collection, a lectotype specimen of C. chiajeana was selected. Botryocladia macaronesica, known so far only from the islands of Azores, Madeira, Canaries and Cape Verde, differs from other Botryocladia species by a unique combination of significant attributes including elongate saccate vesicles, near-continuous cortication of vesicle walls, secretory cells on unmodified medullary cells and completely immersed cystocarps. An analysis of the morphological characters currently used for separating Botryocladia from related genera (i.e. Chrysymenia, Gloiosaccion and Irvinea), showed that there is considerable overlap between Botryocladia and Irvinea. These genera are presently discriminated mostly by molecular evidence as the supposed morphological characters are shown here to vary considerably within the genus Botryocladia.

This article aims to study the homoeologous chromosome pairing and translocation induced by 5A/5R x 6A/6R wheat-rye substitution lines. To clarify the mechanism of homoeologous chromosome pairing and create wheat-rye translocation lines, two wheat-rye substitution lines, 5A/5R and 6A/6R were crossed. The chromosome behavior of pollen mother cells (PMCs) in meiosis was investigated in hybrid F 1 . Homoeologous chromosome pairing between wheat and rye occurred in 22.91% of PMC. Wheat-rye translocation lines were identified via C-banding and in situ hybridization (GISH) in hybrid F 2 and later generations. In F 2 generation, translocations happened in 9 of 45 plants, reached to 20%. These translocation lines were generated from homoeologous chromosome pairing, or mis-division and reconstruction of univalent chromosomes.

We propose a new theory to explain developmental aberrations in plant hybrids. In our theory, hybrid incompatibilities arise from imbalances in the mechanisms that cause male sterility in hermaphroditic plants. Mitochondria often cause male sterility by killing the tapetal tissue that nurtures pollen mother cells. Recent evidence suggests that mitochondria destroy the tapetum by triggering standard pathways of programmed cell death. Some nuclear genotypes repress mitochondrial male sterility and restore pollen fertility. Normal regulation of tapetal development therefore arises from a delicate balance between the disruptive effects of mitochondria and the defensive countermeasures of the nuclear genes. In hybrids, incompatibilities between male-sterile mitochondria and nuclear restorers may frequently upset the regulatory control of programmed cell death, causing tapetal abnormalities and male sterility. We propose that hybrid misregulation of programmed cell death may also spill over into other tissues, explaining various developmental aberrations observed in hybrids.

Biotrophic plant pathogenic fungi often develop a sophisticated series of infection structures for non-destructive host tissue penetration. In vitro, early infection structures of rust fungi-germ tube, appressorium, substomatal vesicle, infection hyphae-can easily be induced, but in vitro differentiation rates of late infection structures-haustorial mother cells (hmc), haustoria-are low at best. Under appropriate conditions (humid atmosphere), a combination of physical (mild heat shock) and chemical signals (trans-2-hexen-1-ol) induced the in vitro differentiation of hmc in the wheat stem rust fungus, Puccinia graminis f. sp. tritici. Around two thirds of the in vitro differentiated germlings developed up to three hmc which were cytologically identical to hmc formed in planta. Efficient in vitro differentiation of hmc will allow us to analyse in molecular detail the processes involved in the induction and differentiation of this critically important developmental stage of the economically important plant pathogenic rust fungi.

Cytomixis (i.e., chromatin migration between meiocytes) has been detected in many plant species, but not in Medicago sativa spp. In the present study we report the identification of a few cytomictic alfalfa plants. Those plants, the "mother plants," were selfed and crossed with a normal control plant. Microsporogenesis analysis was performed on the mother plants, on the S(1) and F(1) plants, and on controls. The S(1) and F(1) plants, like the mother plants, were found to be cytomictic. Single or multiple chromatin bridges between two or more meiocytes were observed almost exclusively in prophase I. Some completely empty meiocytes were also observed. In addition to cytomixis, other meiotic abnormalities were found. Control plants showed an almost regular meiosis. The highest values of cytomixis were observed in the mother plants, and the lowest in their F(1) progenies. Variability of cytomixis in the F(1) plants is probably due to a heterozygotic condition of the parents for this trait. No significant correlation was found between cytomixis and pollen viability, even if the cytomictic plants showed low values of pollen viability.

Publisher Summary The budding yeast Saccharomyces cerevisiae ( S. cerevisiae ) divides asymmetrically. In vegetative growth, yeast cells reproduce by budding, and the position where the bud forms ultimately determines the plane of cell division. This chapter describes the detailed procedures for the separation and isolation of mothers and daughters. These protocols have been used by investigators studying aging, bud site selection, and other aspects of asymmetric cell division. The chapter describes the procedures for performing life span analysis by micromanipulation and the steps for the large-scale collection of old cells. At the beginning and the end of a life span, it can be difficult to distinguish mothers from daughters. At most points in the life span, daughter cells are smaller than the mothers that produced them. In addition, mother cells will generally bud a second time before their daughter cells form their first bud. One method for effective isolation of virgin daughter cells from mother cells, but not for recovery of old mothers, is called a “baby machine.” Mother cells are attached to a membrane and allowed to divide. Daughter cells from these attached cells are eluted continuously by washing the membrane.

Reproductive structures of Laurencia pelagosae are described for the first time. Tetrasporangia, in parallel arrangement, are cut off from the mother cells adaxially; antheridial branches, which are unramified, are inserted in depressions lacking a row of axial cells on their bases; cystocarps are sessile and subspherical. The occurrence of secondary pit-connections between epidermal cells and of lenticular thickenings in the walls of medullary cells is documented. The species is included in the new section Pelagosae within the subgenus Laurencia.

O presente trabalho cita a ocorrência de Trichogloea requienii no litoral da Bahia, nordeste do Brasil. O gênero é caracterizado por apresentar calcificação moderada na região entre os filamentos assimiladores (córtex) e medula, células mães dos espermatângios dispostas em verticilos sobre as células subterminais corticais, carpogônio localizado no final do filamento assimilador e desenvolvimento de filamentos estéreis curtos nas células inferiores do ramo carpogonial. São apresentadas descrição e ilustração detalhadas do táxon, além da comparação com entidades afins. Esta é a primeira citação do gênero para o Atlântico Sul. Trichogloea requienii was collected in Bahia (northeastern Brazil). The genus is recognized easily for presenting moderate calcification between assimilatory filaments (cortex) and medulla, spermatangia mother cells in whorls on subterminal cortical cells, carpogonial branch at the end of the assimilatory filaments and sterile filaments at the lower cells of the carpogonial branch. Description and detailed illustrations of the taxon are presented as well as comparation with related species. This is the first citation of this genus to the South Atlantic.

RFLP analyses were carried out in the progeny from a cross of two phylogenetically distant rice species, wild rice Oryza alta Swallen (CCDD, 2n = 48) and cultivated rice O. sativa L. (AA, 2n = 24). The sterile plants gave heterozygous RFLP patterns at most of the loci detected. They looked more like their wild rice parent, with 36 chromosomes in their root-tip cells and pollen mother cells. In two partially fertile plants, however, most of the markers that were used showed RFLP patterns similar to the cultivated parent, O. sativa. By cytological study, it was found that nearly one-third of the chromosomes had been eliminated in the partially fertile plants. Their seeds have short awns, which is a characteristic of their wild parent, O. alta. An introgression occurred in one of the partially fertile plants, which led to the discussion about a nonconventional mechanism in wide hybridization for transference of wild rice chromosome segments to cultivated rice chromosomes.Key words: RFLP, Oryza alta, rice, Oryza sativa, wide hybridization.

Dissect young ears (2–4 cm long) from husk leaves and fix for 24 hours in Chemberlen’s fixative: 50% ethanol:40% formalin:glacial acetic acid in proportion 90:5:5, and rinse several times in 95% ethanol. Store in 70% ethanol in the refrigerator.

In Chapter 4.4, several different schemes were presented for distinguishing cambial initials from their derivatives (Figs. 4.15, 4.16). According to these schemes, the cambial initials and their immediate derivatives, the xylem and phloem mother cells, were collectively referred to as the cambial zone. However, as pointed out in previous chapters, it is seldom possible to precisely identify cambial initials in histological preparations. Consequently, characteristics of the initials must, by necessity, be determined retrospectively by examining cambial derivatives in various states of differentiation.

In corn, many of the stages of megasporogenesis and megagametogenesis may be harvested from the same ear; an external morphological gradient can be used to find specific stages in the progression. A 2-cm ear will contain the stages of meiosis and megasporogenesis, and those longer than 2 cm will contain later stages of megagametogenesis; developmental stages in the ears follow those in the tassels by about 10 days (D. P. West, unpublished). Silk length will differ between cultivars and plantings, but the following should provide a rough guide: 1–2 mm = megaspore mother cells, 2.5 mm = early tetrad of megaspores, 3.0 mm = late tetrad and early embryo sac, 4.5 mm = 2-nucleate (N) embryo sac, 7.0 mm = 4-N embryo sac, 8.5 mm = 8-N embryo sac, 10 mm to maturity = maturing embryo sac (Russell, unpublished). Fixing a morphological progression (as is present in each ear) will facilitate staging. The normal sequence of development has been reported by Weatherwax (1919), Cooper (1937), and Russell (1979). Earlier stages of floral organ initiation and staging are reported by Cheng et al. (1983).

The microsporocyte material in the young developing tassel is located inside the rolled leaf sheaths. The readiness of material for study of meiosis can be checked by squeezing the upper part of plant stem between the fingers. When the region feels soft, the material is at or near meiosis. Also see Figure 72.37 in the chapter by Chang and Neuffer (this volume) for an orientation to tassel development.

Modelling of plasmid containing cell cultures aids in developing a greater understanding of these complex systems. For such modelling, a number of investigators have introduced key kinetic parameters: the frequency of generation of plasmid-free daughter cells from plasmid-carrying mother cells, the specific growth rate difference between plasmid-carrying (µ+) and plasmid-free cells (µ-) and the probability of plasmid loss pr [1,2,3]. However, little experimental data have been reported [4,5]. In the previous paper the probability of plasmid loss pr varies with the growth rate of the plasmid-carrying cells µ+ [6]. We propose a modelling approach, allowing the simulation of this variation.