Tetrad Cells Research Articles

Phenomenon of cell breakdown and phenotypic observation on surviving blades in inter-species hybridization progeny between pigment mutants of Pyropia haitanensis and P. acanthophora (Bangiales, Rhodophyta)

Pyropia haitanensis is a species of red algae native to China. Its meiosis occurs during the first two divisions of germinating conchospores and a tetrad with different genotypes is formed in the second division. Then each cell continues to undergo mitosis and finally, the conchosporeling develops into a genotype chimeric blade. Conchospores were formed from the inter-species hybridization between a red-type pigmentation mutant of P. haitanensis and a green-type pigmentation mutant of Pyropia acanthophora, among which, a phenomenon of serious cell breakdown occurred in the early developmental stage of germination. The phenomenon of cell breakdown occurred not only in the direct products of meiosis (conchosporelings containing 2–4 cells), but also in conchosporelings whose cell number was more than four, but large-scale cell breakdown occurred in conchosporelings containing 3–4 cells. After 35 days in culture, 99.2% of conchosporelings was unable to form thallus due to the heavy breaking down of somatic cells and only about 0.8% of the conchosporelings could form thallus, but most of them could not develop from the complete tetrads but just developed from 1 to 2 surviving tetrad cells. The F1 gametophytic blades developed from conchospores showed two parental colors (R and G) and four new colors (R’, redder in color than R; G’, lighter in color than G; T, tawny in color; W, light brown in color). The results confirmed that the hybrid breakdown of Pyropia could not only be used to assist in the more accurate identification of species; but also could be used to select new strains with recombination advantage from the surviving offspring.

Pollen development in male sterile mangosteen (Garcinia mangostana L.) and male fertile seashore mangosteen (Garcinia celebica L.).

Mangosteen (Garcinia mangostana L.) is an economically important tropical fruit, yet the reproductive biology of this dioecious plant is complex. Male trees are not known, and female trees have sterile anthers leading to apomixis. We hypothesized that pollen abortion in mangosteen is due to altered tapetum activity during microgametogenesis. Developmental events at the cellular and sub-cellular levels during pollen development in G. mangostana were therefore examined and compared with seashore mangosteen (G. celebica L.), a closely related species with fertile anthers. In G. mangostana, the microspore mother cell had disorganized cytoplasm, including lack of Golgi apparatus and its vesicles, as well as abnormal callose wall accumulation. Globular droplets, which resembled orbicules or Ubisch bodies, were abundant in the locule, including pre-Ubisch bodies found along the tapetal plasma membrane. The tapetum of G. mangostana underwent cell death earlier than the fertile G. celebica, and during the premature death, the mitochondria had dramatically altered shapes. Low accumulation of starch in collapsed microspore mother cells and tetrad cell remnants also suggested that altered cell metabolism is related to pollen abortion in mangosteen. The present results demonstrate the importance of coordinated development between the tapetum and microspores in pollen development and provide new insights into male sterility in mangosteen (G. mangostana).

Morphogenesis and spontaneous chromosome doubling during the parthenogenetic development of haploid female gametophytes in Pyropia haitanensis (Bangiales, Rhodophyta)

Pyropia haitanensis is one of the most economically important seaweeds growing in the coastal regions of south China. Previous studies revealed that parthenogenesis could emerge in P. haitanensis under certain culture conditions. In the present study, detailed cytological observations were made of morphogenesis and chromosomal behaviors of female gametophytes of P. haitanensis during parthenogenesis. Unisexual cultures of female gametophytes, derived from isolated somatic cells of wild gametophytes or obtained from cloned sporophytes, ultimately led to their development into parthenosporophytes. Based on the changes in shape and color of the cellular chromatophore, as well as the metamorphosis and condition of the released cells, the parthenogenesis of P. haitanensis was divided into six developmental stages: vegetative cells (VCs) with multiple stellate chromatophores, carpogonium-like cells (CLCs) with dispersed chromatophores, carpogonium-like protoplasts (CLPs) released post-cell wall dissolution, carpospore-like cells (CCs) with regenerated cell wall, carpospore-like germlings (CGs), and parthenosporophytes. Chromosomal observations showed that VCs were haploid (n = 5), small proportions of CLCs, and CLPs and CCs were diploid (2n = 10), while all the CGs, filamentous conchocelis cells, and conchosporangial branch cells of parthenosporophytes were diploid (2n = 10). Haploid, aneuploid, and polyploidy were not observed in the latter group of cells. Spontaneous chromosome doubling occurred during the parthenogenesis of P. haitanensis, first in highly differentiated CLCs. Furthermore, pit connections could be seen throughout the parthenosporophyte development process similar to that in heterozygous sporophytes. The chromosomes were seen undergoing meiosis during the germination of conchospores released from mature parthenosporophytes, leading to the generation of tetrad cells, which developed into haploid female gametophytes. These results provide evidence for better understanding the mechanism underlying parthenogenesis in Pyropia.

Micronucleus Assay with Tetrad Cells of Tradescantia.

The Tradescantia micronucleus assay has been used since 50years for the detection of genotoxins (including carcinogens) in the environment. A large database concerning the effects of individual chemicals and complex environmental mixtures (soil, airand waters) has accumulated. In contrast to other mutagenicity test systems, the effects of low concentrations of heavy metals, radionuclides, certain herbicides, pesticides and gaseous mutagens can be detected and it is also possible to conduct in situ biomonitoring studies with plant. The test system has been validated and standardized protocols have been developed for laboratory experiments and for field studies which are described in this chapter.

Revisiting Meiosis in Sugarcane: Chromosomal Irregularities and the Prevalence of Bivalent Configurations.

Traditional sugarcane cultivars (Saccharum officinarum) proved highly susceptible to diseases, and this led breeders to progress to interspecific crosses resulting in disease resistance. A backcrossing program to S. officinarum was then required to boost sucrose content. Clonal selection across generations and incorporation of other germplasm into cultivated backgrounds established the (narrow) genetic base of modern cultivars (Saccharum spp.), which have a man-made genome. The genome complexity has inspired several molecular studies that have elucidated aspects of sugarcane genome constitution, architecture, and cytogenetics. However, there is a critical shortage of information on chromosome behavior throughout meiosis in modern cultivars. In this study, we examined the microsporogenesis of a contemporary variety, providing a detailed analysis of the meiotic process and chromosome association at diakinesis, using FISH with centromeric probes. Chromosomal abnormalities were documented by examining high quality preparations of pollen mother cells (700 in total). Approximately 70% of the cells showed abnormalities, such as metaphase chromosomes not lined up at the plate, lagging chromosomes and chromosomal bridges, and tetrad cells with micronuclei. Some dyads with asynchronous behavior were also observed. Due to the hybrid composition of the sugarcane genome, we suggest that bivalent incomplete pairing may occur in the first prophase leading to univalency. The presence of rod bivalents showing the lagging tendency is consistent with a reduction in chiasma frequency. Finally, the presence of chromatin bridges indicates the indirect occurrence of chromosomal inversions, although chromosome fragments were not clearly recognized. Possible reasons for such meiotic abnormalities and the large prevalence of bivalent formation are discussed.

10. Isolation and Identification of Lactic Acid Bacteria Genus Pediococcus from Sumatran Orangutan (Pongo abelii) faeces at Kandi Zoo and Kinantan Zoo West Sumatera

This research has purposes to isolating and identifying the lactic acid bacteria genus Pediococcus in sumatran orangutan (Pongo abelii) feaces. Feaces are isolated from one orangutan at Kandi Zoo and two orangutans at Kinantan Zoo. The isolating of the lactic acid bacteria was done by using streak plate method with the MRSA (de Man Rogosa Sharpe Agar) specific media. Identification was done by the morphological observing, Gram stain, catalase test, oxidase test and biochemical test. The result showed that one isolate feaces from Kandi Zoo has cocci shaped with the isolate prediction approaches genus Pediococcus sp. The characteristic features of isolate are cocci shaped, Gram positive, tetrad cell structure, nonmotile, catalase negative, and oxidase negative. Based on these characteristics, it can be concluded that there is a lactic acid bacteria coloni which grouped into genus Pediococcus in male orangutan feaces from Kandi Zoo

Traffic-related air pollution biomonitoring with Tradescantia pallida (Rose) Hunt. cv. purpurea Boom in Brazil.

This study aimed to verify the capacity of Tradescantia pallida in the biomonitoring of air pollution in urban areas with different traffic intensities and under varying environmental conditions. Experiments were carried out in Ribeirão Preto, in the Southeastern Brazil, with more than 660,000 inhabitants and a fleet of more than 485,000 motor vehicles. Ten seedlings of T. pallida were exposed in three areas in the city, differing in traffic vehicle flow, in two seasons (wet and dry). At the end of each sampling period, which lasted 4 months, samples of leaves were collected, and the content of As, Ba, Ca, Cd, Cr, Cu, Fe, Hg, Mg, Mn, P, Pb, S, and Zn was determined by inductively coupled plasma mass spectroscopy (ICP-MS). The same elements were determined in soil samples for a seasonal characterization in conjunction with secondary data of environmental parameters. Additionally, micronucleus assay with early pollen tetrad cells of Tradescantia (Trad-MN) was conducted by collecting flower buds and analyzing the micronuclei frequencies in pollen mother cells. Although pollutant levels in air were below the Brazilian legal limits, plants exposed in the high-traffic flow area presented higher concentrations of elements related to vehicle emissions, especially under dry conditions, and higher micronuclei frequency in pollen mother cells. These results show the sensitivity of T. pallida to low-level urban air pollution and its suitability as bioindicator for trace elements. This alternative tool for biomonitoring can serve as a support methodology for the adoption of more restrictive public environmental policies in Brazil and extendible to other developing countries.

Effects of atmospheric pollutants on somatic and germ cells of Tradescantia pallida (Rose) D.R. Hunt cv. purpurea.

Anatomical alterations in leaves and DNA damage in cells caused by the accumulation of atmospheric pollutants can be measured by epidermal leaf analyses and Tradescantia micronuclei assay with early pollen tetrad cells. The present study examined the feasibility of using somatic and germ cells of Tradescantia pallida for biomonitoring purposes in the city of Dourados, state of Mato Grosso do Sul (MS), Brazil. Stomatal, micronucleus and epidermal leaf analyses were performed, using standard methodologies, on plants growing at three locations during six different time periods. Tradescantia micronuclei data were analyzed using SAS 9.2 software package and stomatal data were analyzed using SANEST software. Analyses of stomatal characteristics and micronuclei examination in T. pallida were found to be an efficient tool for monitoring atmospheric pollution. The micronucleus assay suggested that the number of micronuclei in early pollen tetrad cells was related to the intensity of vehicular traffic. Increased number of epidermal cells and stomata and increased stomatal density observed at locations with greater vehicular traffic are likely physiological responses of those plants to the increased gas exchange in highly polluted environments.

Acute toxic and genotoxic activities of widely used cytostatic drugs in higher plants: Possible impact on the environment

Cytostatic drugs are highly toxic pharmaceuticals and it was repeatedly postulated that they may cause adverse effects in ecosystems. The acute toxic and genotoxic properties of these drugs have not been adequately investigated in higher plants so far; therefore, we studied the most widely used drugs (5-flurouracil, 5FU; etoposide, Et; cisplatin, CisPt; carboplatin, CaPt; vincristine sulfate, VinS and cyclophosphamide monohydrate, CP) in micronucleus (MN) assays with meiotic pollen tetrad cells of Tradescantia and with root cells from Allium cepa. MNi are formed as a consequence of chromosome breaks and aneuploidy. We monitored also the acute toxic properties of the drugs, i.e. inhibition of cell division (mitotic indices and retardation of root growth) in the latter species. All compounds caused in both indicator plants genotoxic effects. The order of genotoxic potencies expressed as NOELs in µM was CisPt (0.1)≥Et (0.5)>CP (1.0)>CaPt (10)>5FU (30)>VinS (100) in Tradescantia. A similar order was seen in Allium MN but Et was less active (5.0µM). Four compounds caused alterations of the mitotic indices under the present conditions namely CisPt (0.5), Et (10.0), 5FU (10.0) and VinS (100). Inhibition of root growth decreased in the order CisPt (0.5)>Et (1.0)≥VinS (1.0)>5FU (5.0)>CaPt (33.0)>CP (>1000). Comparisons of the NOELs with the predicted environmental concentrations (PEC) show that the latter values are at least 5 orders of magnitude lower and indicate that it is unlikely that their release in the environment may cause adverse effects in higher plants. However, it is notable that the levels of both platinum compounds and of 5FU in hospital effluents may reach levels which may induce damage of the genetic material.

Assessment of genotoxicity and acute toxic effect of the imatinib mesylate in plant bioassays

Imatinib mesylate (IM) is at present one of the most widely used cytostatic drugs in developed countries but information on its ecotoxicological activities is scarce. This article describes the results of the first investigation in which genotoxic and acute toxic properties of the drug were studied in higher plants. IM was tested in two widely used plant bioassays namely in micronucleus (MN) assays with meiotic tetrad cells of Tradescantia (clone #4430) and in mitotic root tip cells of Allium cepa. Additionally, acute toxic effects (inhibition of cell division and growth of roots) were monitored in the onions. Furthermore, we studied the impact of the drug on the fertility of higher plants in pollen abortion experiments with three wildlife species (Chelidonium majus, Tradescantia palludosa and Arabidopsis thaliana). In MN assays with Tradesacantia a significant effect was seen with doses ⩾10μM; the Allium MN assay was even more sensitive (LOEL⩾1.0μM). A significant decrease of the mitotic indices was detected at levels ⩾10μM in the onions and reduction of root growth with ⩾100μM. In the pollen fertility assays clear effects were observed at doses ⩾147.3mgkg−1. Data concerning the annual use of the drug in European countries (France, Germany, Slovenia) enable the calculation of the predicted environmental concentration (PEC) values which are in the range between 3.3 and 5.0ngL−1. Although comparisons with the genotoxic potencies of other commonly used cytostatic drugs and with highly active heavy metal compounds show that IM is an extremely potent genotoxin in higher plants, it is evident that the environmental concentrations are ⩾5 orders of magnitude lower as the levels which are required to cause adverse effects.

Evidence for second division restitution as the basis for 2n + n maternal chromosome transmission in a sugarcane cross

Chromosome doubling in megaspores of sugarcane was first reported over 70 years ago and was seen primarily in interspecific crosses between Saccharum officinarum and Saccharum spontaneum. Since then, there has been robust debate on the mechanism(s) responsible for this doubling with hypotheses ranging from second division restitution (SDR), post-meiotic restitution to fusion of the two innermost cells of the megaspore tetrad. In the present study, we sought to answer this question using molecular marker data from a cross which demonstrated 2n + n chromosome transmission between an S. officinarum clone (IJ76-514; 2n transmission) and a commercial hybrid (Q165 ; n transmission). Molecular marker data from four other bi-parental crosses were used to form a “base-line” for expected segregation ratios (n + n transmission). Comparison of segregation ratios showed that 2n transmission from the S. officinarum clone could be identified by the increased segregation ratios, a characteristic of both SDR and tetrad cell fusion. Simulation was then undertaken based on current understandings of sugarcane meiosis, to determine if the observed segregation ratios matched those simulated for SDR/tetrad cell fusion. Analysis of the simulation confirmed that most and perhaps all progeny appear to have been formed from a mechanism akin to SDR/tetrad cell fusion. The genetic consequences of this are discussed.

Micronucleus assays with Tradescantia pollen tetrads: an update

Micronucleus (MN) assays with early pollen tetrad cells of Tradescantia (Trad-MN assays) are at present the most widely used bioassays with plants for the detection of genotoxins in the environment. So far, ∼ 160 chemicals have been tested and ∼ 100 articles that concern complex environmental mixtures were published. This article summarises the results of Trad-MN studies, which have been carried out during the last 15 years with individual compounds and investigations concerning the pollution of environmental compartments (soil, water and air). The evaluation shows that the effects of certain genotoxins such as heavy metals, radionuclides, pesticides and air pollutants can be easily detected with this test. Comparisons with results obtained in MN studies with mitotic (root tip) cells indicate that meiotic tetrad cells are in general more sensitive. Important issues for future research concern the evaluation of the suitability of wildlife Tradescantia species that are sometimes used instead of specific clones (such as #4430 for which standardised protocols have been developed) as well as the assessment of the predictive value of Trad-MN results in regard to the prediction of cancer hazards in humans and adverse effects at the ecosystem level. The fact that the genotoxic effects of certain compound such as metals, which can be detected with plant bioassays, in particular with the Trad-MN assay but not in other commonly used bioassays (e.g. in bacterial tests) makes them an essential element in the batteries for environmental monitoring.

Megasporogenesis and Megagametogenesis in Autotetraploid Indica/Japonica Rice Hybrid

Autotetraploid indica/japonica rice hybrid combines both the advantages of polyploidy and the heterosis between indica and japonica rice. Embryo sac abortion is an important factor influencing spikelet fertility in autotetraploid rice hybrid. To clarify the cytological mechanism of embryo sac abortion, the megasporogenesis and megagametogenesis in an autotetraploid japonica/indica hybrid were examined by the whole-mount eosin B-staining confocal laser scanning microscopy (WE-CLSM) technique. Abnormalities were observed from the megasporocyte stage to the mature embryo sac stage. The degeneration of the tetrad cells and the functional megaspore was the characteristic of abnormalities during megasporogenesis. Abnormal small embryo sacs and disordered number of nuclei were frequently observed during embryo sac development. Some interesting phenomena, such as two functional megaspores, the diplospory-like megasporocyte, and five-nucleate embryo sac were found. The abnormalities that occurred during female gametophyte development resulted in more than five types of abnormal embryo sacs (i.e. embryo sac degeneration, embryo sac without female germ unit, embryo sac without egg apparatus, embryo sac with abnormal polar nuclei and abnormal small embryo sac) in autotetraploid japonica/indica hybrid. Embryo sac fertility was lower in diploid japonica/indica hybrid than in autotetraploid japonica/indica hybrid although many abnormal phenomena were observed in autotetraploid hybrid.

Early signs of heat stress-induced abnormal development of anther in rice

田间条件下持续高温(而非短期高温)是导致水稻生殖生长期高温危害的重要条件, 由此推测水稻花粉母细胞减数分裂至抽穗的一段期间, 可能均为水稻的高温敏感期, 且高温诱导可能具有累积效应。本研究模拟田间典型灾害天气条件, 在人工气候箱内对杂交水稻"金优63"花粉母细胞减数分裂期进行连续3 d的热害胁迫处理, 对处理后不同发育时期的花药组织取样切片观察, 从组织、细胞水平探讨水稻受高温胁迫后花药可能出现的早期异常特征。结果表明, 受高温胁迫后, 在小孢子形成阶段, 水稻花粉母细胞发育异常、四分体无法适时分散; 在花粉粒成熟阶段, 水稻生殖细胞失去正确的排列方向、绒毡层细胞发生非正常分解、花药壁和花粉粒发生形态异常并出现败育。此外, 植株减数分裂期受高温胁迫后, 开花时花粉活力显著降低。这些结果表明, 抽穗前的高温直接导致水稻花药组织和生殖细胞异常发育, 从而减少有效花粉的形成和降低裂药与授粉性能, 可能成为田间条件下持续高温引起水稻不育的重要原因。

Meiotic Behavior of Wild, Synthetic and Cultivated Wheats

Wild relatives of bread wheat are potential sources of valuable genetic materials for wheat improvement. Genomic relationship and cross-ability between plant species can be deduced from chromosomal structure, size and behavior during meiotic division. In this study, the meiotic behavior of 21 wheat genotypes possessing the 3 ploidy levels of diploid, tetraploid and hexaploid and belonging to 3 wild, cultivated and synthetic growing statuses was investigated. The results indicated that the average number of ring bivalents at metaphase I ranged from 60 to 100% in the studied genotypes with the lowest rate belonging to the diploid wild relative wheat species. Four meiotic abnormalities including (1) precocious chromosome migration to the poles at metaphase I, (2) laggard chromosomes at anaphase I and telophase I, (3) chromosome stickiness and chromosome bridge at anaphase I and (4) formation of micronuclei at telophase I and in the tetrad cells were found in the studied genotypes. The highest meiotic abnormalities were found in synthetic wheat accessions. The average value of the meiotic index for the studied wheat genotypes was above 99%, revealing their normal meiotic behavior.

STUDIES OF MEIOSIS IN LUZULA PURPUREA

In Luzula purpurea, which has diffuse centromeres and only six chromosomes, a study was made of the separation of chromatids during the first meiotic division, the pairing of the free chromitids at interkinesis, and the chromosomes of first mitosis of the pollen tetrads. Two strains were used, the normal type of L. purpurea with 2n = 6, and certain plants selected among the x- irradiated survivors. The normal plants had six somatic chromosomes of equal size that could not be distinguished from each other. The x-irradiated plants originated from material treated with 2500 or 1000 r as seedlings. Mitotic chromosome patterns were examined in progenies of the treated plants. Several of the irradiated plants were found to have 2n = 7 with five normal-sized chromosomes and one chromosome fragmented into two pieces of about equal size. Pairing of chromosomes during meiosis in these irradiated plants was compared with that in the normal L. purpurea with 2n = 6, and the distribution of large and small chromosomes between the four cells of the pollen tetrads was examined. Five of the original six chromosomes were unaffected by the x-ray treatment. A study of meiosis verified the postulated type of fragmentation of themore » 6th one. One heteromorphic association is formed in each cell of meiosis, originating from the pairing between the two fragments and their homologous unbroken partner. The association is open at metaphase and separates equationally during first anaphase. In the tetrad the two fragments regularly substitute the broken chromosome. The plants behave cytologically in the same way as the hybrids between diploid strains and naturally occurring endonuclear polyploids with half-sized chromosomes. In the next generation plants homozygote for the fragmented chromosome were found, showing a regular meiosis with two large and two small bivalents. The origin of the single fragmented chromosome in the irradiated material is difficult to explain; however, it was found earlier that chromosomes broken by x rays may persist as fragments in L. purpurea. It is noteworthy that the result of the fragmentation corresponds to the naturally occurring changes of chromosome pattern found in the genus Luzula. The pairing behavior of the chromosomes during meiosis in the heterozygote is the same as the one described for corresponding hybrids of L. campestris as well as the distribution of the large and the small chromosomes between the tetrad cells, where two half-sized chromosomes always substitute one large one. In such a case the progeny plants, homozygous for the fragmented chromosome, can give rise to a population which may be considered as an artificially produced endonuclear aneuploid strain, similar to the ones naturally found in the genus Luzula. (BBB)« less

Ultrastructure in Microspore Abortion of Genic Male Sterile Line in Sesame ( Sesamum indicum L.)

To investigate the abortion mechanism of genic male sterile (GMS) line in sesame ( Sesamum indicum L.), a comparative study was conducted on the fertile and sterile microsporogenesis of ms86-1 using transmission electron microscopy (TEM) techniques. According to the morphologic characteristics of the microspores, the developmental process of sesame pollen could be tentatively divided into 7 stages, namely microsporocyte formation, microsporocyte meiosis, tetrad, early microspore, middle microspore, late microspore, and pollen maturation stage. The abnormal phenomena observed in sterile anthers indicated that male sterility might arise in microsporocyte formation stage. With the growth and development of sterile anthers, cell walls of the sterile microsporocytes were irregular during their formation. In the meiosis stage, the cell walls were distorted obviously, and the microsporocytes failed to form the early exine component designated as probaculums on the outside of the plasma membrane. Subsequently, abnormal villiform deposits were observed on the outside of the callose wall at the tetrad stage. As soon as the tetrad cells disintegrated, the released sterile microspores represented aberrantly dumbbell-shaped, and their exines were undergrown without any baculum. Accompanying with delay of the degeneration process, inclusions of the tapetum cells became more abundant and few abnormal ubisch bodies were secreted. Later on, the sterile microspore was gradually crimpled as its cytoplasm agglomerated to an electron dense clot, and ultimately degraded to the complete abortion.

Ontogeny of the Calliandra – massulae (Mimosaceae: Ingeae), and the associated viscin body

Polyads, called also massulae, are common in the Mimosaceae. Within this family, only in Calliandra (s. l.) polyads show a remarkable morphological variation: 16-grained lens-shaped massulae in the neotropical Zapoteca (syn. Calliandra p.p.), and highly asymmetric eight-grained massulae in Calliandra (s. str.). As a further specialisation the massulae in Calliandra (s. str.) possess a sticky appendage called a viscin body. The form and ontogeny of this unique two-dimensional construction of the massula is of particular interest. In Calliandra (s. str.) the octad is normally the developmental product of the initiation stage, beginning with one pollen mother cell (PMC). In total, Calliandra (s. str.) possesses eight PMCs in each anther. The dicotyledons are characterised by the simultaneous type of cytokinesis, but wall formation in Calliandra (s. str.) during meiotic division is successive, as common in monocotyledons. The first wall divides the PMC diagonally, and during the tetrad period, two clear variants of tetrads are found. One shows the typical rhomboidal arrangement and the other forms two congruent symmetrical halves. The latter probably results from early fixed, quite inflexible walls. The cells of tetrad do not separate, and four successive mitotic divisions give rise to the eight-celled massula. The direction of growth of the PMC and the massula, the sequence of division, and the position of the walls all show a strict polarity. The normal number of eight cells in each massula is sometimes exceeded without loss of viability. Calliandra (s. str.) lacks a developed “Pollenkitt”, and its asymmetrical massula is combined with the viscin body, which is involved in pollination. This viscin body is located on a specialised pollen grain at the top of the massula. With the viscin body, Calliandra (s. str.) massulae have a mechanism for immediate and persistent attachment to different surfaces. SEM is used to understand the mechanisms of attachment in detail. Furthermore, the relation between pollinators and the massula shape is investigated. Massula transport and the role of the viscin body in pollen–stigma interaction are discussed as well. The stigma of Calliandra (s. str.) is papillate and in the receptive stage, it is characterised by acquisition of a copious exudate. Zapoteca (syn. Calliandra p.p.) massulae could be distinguished histochemically from those of Calliandra (s. str.) by the main components of the “Pollenkitt”. Histochemical and physical properties of the viscin body suggest a waxy nature, including lipids in combination with unsaturated fatty acids. Proteins are present in less amounts and polysaccharides and polyglucans are absent. These results are discussed in relation to analogous phenomena in other families. The term “apex cell” is introduced to indicate the specialisation of the tip-cell of the massula by ontogeny and polarity.

Electron-translucent angular areas in developing tapetum cell walls and pollen grains ofTilia platyphyllos

InTilia platyphyllos, the anther tapetal cell walls undergo significant modifications from the tetrad stage onwards. During the tetrad stage the inner tangential and radial parts of the tapetal walls begin to dissolve, while the distal parts swell. After the tetrad stage, the distal and outer radial tapetal cell walls become covered by a thick, irregular, highly electron-dense, polysaccharide layer. Striking features of the maturing tapetal walls (microspore stage and later) are electron-translucent, structureless, unstainable angular areas of variable dimensions. Similar electron-translucent areas occur in the exine arcades and apertures, but also isolated in the locular fluid ofT. platyphyllos. Electron-translucent areas, that are also found in the exine arcades and tapetal cells of other angiosperms, can be interpreted as the products of poorly understood metabolic processes.

Monitoring the genotoxicity of soil extracts from two heavily polluted sites in Prague using the Tradescantia stamen hair and micronucleus (MNC) assays

We have taken soil samples from two sites in Prague, the capital of the Czech Republic, that are heavily polluted by motor vehicles. As a negative control, soil samples from a recreational site in Prague with no motor vehicle traffic were used. Soil samples from these sites were extracted with water or 5% dimethylsulphoxide (DMSO) for 24 h and cuttings of Tradescantia clone 4430 were immersed for 12 h at 25°C in the extraction solutions. As a positive control Tradescantia plants have been treated with the promutagenic arylamine o-phenylenediamine at the same treatment conditions. None of the tested soil extractions significantly increased the frequency of somatic mutations in the stamen hair assay. By contrast, a 5% DMSO soil extract from one of the tested sites (entrance of the Letná tunnel) significantly increased the frequency of micronuclei (MNC) in the pollen mother tetrad cells. A repetition of the treatment 14 days later also resulted in an increase in the frequency of MNC, however the increase was not statistically significant. This study was conducted for the International Programme on Plant Bioassays.