Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Op weg naar homozygote planten uit microsporen van bolgewassen : eindverslag van het project "In vitro selectie met behulp van microsporen bij bolgewassen"
    Bulk, R.W. van den; Vries-van Hulten, H.P.J. de; Dons, J.J.M. - \ 1994
    Wageningen : CPRO-DLO - 19
    embryokweek - embryozak - bloembollen - stuifmeel - sporen - weefselkweek - tulipa - lilium - in vitro selectie - embryo culture - embryo sac - ornamental bulbs - pollen - spores - tissue culture - in vitro selection
    Revision of Ancylobotrys Pierre. Series of Apocynaceae XXXVII.
    Vonk, G.J.A. ; Leeuwenberg, A.J.M. ; Haegens, R.M.A.P. - \ 1994
    In: Series of revisions of Apocynaceae XXXVII, XXXVIII and pollination of Apocynaceae Wageningen : Agricultural University - ISBN 9789067543613 - 81
    apocynaceae - taxonomische revisies - bestuiving - embryozak - sporen - stuifmeel - apocynaceae - taxonomic revisions - pollination - embryo sac - spores - pollen
    The Tapetum: cytology, function, biochemistry and evolution
    Hesse, M. ; Pacini, E. ; Willemse, M.T.M. - \ 1993
    Berlin : Springer Verlag - ISBN 9783211824863 - 152
    biochemie - embryozak - metabolisme - stuifmeel - polymeren - sporen - celfysiologie - biochemistry - embryo sac - metabolism - pollen - polymers - spores - cell physiology
    The anther tapetum, present in all land plants, is a highly specialized, transient tissue surrounding the (micro-)spores and/or pollen grains during their development.Any tapetum malfunction causes male sterility. The exact knowledge of tapetum form and function therefore is indispensable not only for basic research, but also and especially in plant breeding and plant genetics.In fourteen contributions by reknown experts, a comprehensive account of the various characters and functions of the tapetum is provided, covering the areas of cytology, cytophysiology, biochemistry, tapetum development and function.
    Pollen tube - pistil interaction and fertilization in Lilium longiflorum
    Janson, J. - \ 1992
    Agricultural University. Promotor(en): M.T.M. Willemse. - S.l. : Janson - 145
    liliaceae - bestuiving - embryozak - sporen - stuifmeel - lilium longiflorum - liliaceae - pollination - embryo sac - spores - pollen - lilium longiflorum

    In this thesis the interaction between pollen tube growth and the pistil with the subsequent fertilization was studied both in intact flowers and after different flower manipulations and in vitro pollination. light and electron microscopy and electrophoresis were used.

    To achieve interspecific crosses in lily the cut-style pollination, in which the style is cut off just above the ovary and pollen grains are applied at the cut surface, is used. Just a few ovules are penetrated by a pollen tube. In an intraspecific compatible combination the penetration percentage of the ovules after cut-style pollination is however low as well. Complications occur in the interaction between the pollen tube and the ovule. It might be that the ovules lack an enhancement which takes place during pollination or germination at the stigma or during pollen tube growth in the style, which is absent after cut-style pollination.

    In chapter 1 a review is given of compatible, incompatible and interspecific pollen tube growth in Lilium, the guidance of the pollen tube and other aspects of the interactions between the pollen tubes and the pistil. Following this chapter interactions are first studied in an intact system of Lilium longiflorum .

    In chapter 2 the exudate production in the pistil, embryo sac development and pollen tube growth in L. longiflorum is studied and related to flower bud length and flowering stage. The exudate production on the stigma and in the style starts before the bud opens, as determined by cryo scanning electron microscopy. Just underneath the stigma the exudate first accumulates at the top of each secretory cell, followed by a merging of those accumulations as exudate production proceeds.

    After germination the pollen tubes grow across the stigma and enter the style in between the three stigma lobes. This growth over the stigma seems at least at first not directed. In the style the pollen tubes grow straight downward at a constant speed and are covered by exudate. As the pollen tube bundle reaches the ovary, the secretory pathway and thus also the pollen tube bundle is divided into three ovarian cavities. Hereby they spread out, but their growth is restricted to the area with secretory cells. The secretory cells covering the placenta are similar to those present in the stylar canal, although their surface shape is more spherical rather than elongated as in the style. The transfer wall of the placenta] cell is originating from fusing Golgi vesicles but the endoplasmic reticulum (ER) seems to have an important role as well.

    In between the two rows of ovules in one ovarian cavity a pollen tube bundle is formed in the exudate produced by the placental cells. After neglecting the first few ovules the pollen tubes bend from this bundle in between the ovules and grow towards the micropylar side. There they bend again to stay close to the secretory cells. At anthesis a part of the embryo sacs are in their seven-nucleate and six-cellate (the cell walls in the embryo sac were hard to detect after clearing) stage, i.e. mature. Penetration of the pollen tubes into the micropyle has only been observed in these ovules.

    About 8 days before anthesis exudate is observed in a flower bud. Pollen tube growth in the style is possible from seven days before anthesis. The pollen tube growth is then however strongly retarded compared with the pollen tube growth in a flower at anthesis. It seems that some pollen tubes are not covered by an exudate layer. Newly appearing pollen tube tips have a tendency to grow close to the secretory cells, resulting in a growth between these cells and preceding pollen tubes. If there is still little exudate produced it results in a lifting up of the pollen tubes, out of the exudate.

    The development of the embryo sacs in sector two (sector one is at the top and four is at the basis of the ovary) is ahead of the embryo sacs in the other sectors of the ovary. Pollination or pollen tube growth did not influence the development of the embryo sacs. When the pollen tubes formed after pollination of a flower bud finally reach the ovary, a part of the ovules have matured. From four days before till seven days after anthesis, pollination results in penetration of the ovules. The protein pattern of the ovules observed after electrophoresis did not show a consequent change in the period from anthesis till 9 days after anthesis or 7 days after pollination.

    In chapter 3 the ultrastructure of the embryo sac, the nucellus and parts of the micropyle of L.longiflorum is studied both before and after pollination. Before pollen tube penetration the three cells of the egg apparatus cannot be distinguished, neither in structure nor in their position. No filiform apparatus was detected, no degeneration of a synergid occurs without pollen tube penetration. The polar nuclei in the central cell do not fuse until fertilization. The metabolic activity of the cells of the egg apparatus and the central cell seems low. The nucleus of the most chalazal of the two antipodals has an irregular shape and in some embryo sacs a third antipodal cell, small in size and without a nucleus, is present. Pollen tube growth does not induce changes in the embryo sac.

    When the pollen tube arrives at the nucellus the cuticle surrounding this nucellus is lifted up. Enzymatic digestion of the cell wall of the at this place one cell layer thick nucellus has to take place to create a pathway for the pollen tube to enter the embryo sac. After entering the embryo sac, the pollen tube grows along the inside of the nucellus and finally penetrates one of the three cells of the egg apparatus, now distinguished as the degenerated synergid. Shortly after fertilization two enucleate cytoplasmic bodies of a different ribosome density were observed in the degenerated plasma of the synergid and the pollen tube. These structures border both the central cell, the egg cell and each other and are most likely the two empty sperm cells. The sperm nucleus in the central cell is probably transported by ER and first makes contact with the haploid polar nucleus which is, as the triploid polar nucleus, connected with ER as well. In the egg cell another process is more likely, because here strands of ER were not observed. Here the nuclei line up before fusion. The cells of the embryo sac become more metabolic active after pollen tube penetration. In this chapter an attempt is made to relate ultrastructure to function and processes.

    In chapter 4 the pollen tube growth in the ovary after cut-style pollination was observed with scanning electron microscopy. Different flower manipulations were carried out in an attempt to elucidate the interaction between the pollen tube growth and the pistil. Until the arrival of the pollen tube at the inner integument, the pollen tube growth did not show any difference between cut-style and stigmatic pollination, as studied in chapter 2. Using cut-style pollination the pollen tubes either grew past the inner integument and ignored it, or grew along but not into the micropyle or penetrated the micropyle.

    Grafting a stigma just above the ovary did not influence the penetration percentage, nor did a possible activation of the ovary induced by pollination or pollen tube growth in the style or even in the ovary itself, preceding or during cut-style, interstylar or placental pollination in a pistil. The percentage of penetration after cut-style pollination increased however when the stylar part present at the ovary was left longer.

    The presence of the ovary did not influence the pollen tube growth in the style as determined after isolation of styles from the ovary and comparing the pollen tube length.

    When pollen grains and stigmatic exudate were applied through a slit half-way down the style of an intact pistil the pollen tube growth was not influenced by a simultaneous pollination at the stigma.

    In chapter 5 placental pollination was carried out predominantly with L.longiflorum to study the interaction between the pollen tube and the placenta with ovules. The percentage of penetrated ovules is low when compared with compatible pollination at the stigma. After placental pollination the pollen tube growth between the ovules seems directed and the pollen tubes do find the inner integument. A reaction to the inner integument or the micropyle is observed, but hardly results in ovule penetration. Embryos were found, but did not develop vigorously. The similarities and differences with cut-style pollination, in which the percentage of ovule penetration is also low, are discussed. Grafting a style with pollen tubes to the placenta increased the penetration percentage obtained after placental pollination five times.

    In chapter 6 the data from chapter 2 and 3 are combined in a reproductive calendar.

    In chapter 7 the reproduction is considered as a regulated interaction process. Previous experimental results are considered as aspects of the system and are discussed in this context.

    A comparative ultrastructural study of the megagametophytes in two strains of Zea mays L. before and after fertilization.
    Lammeren, A.A.M. van - \ 1986
    Wageningen : Agricultural University (Agricultural University Wageningen papers 86-1) - ISBN 9789067540889 - 37
    zea mays - maïs - embryozak - zea mays - maize - embryo sac
    Megasporogenesis : a comparative study of the ultrastructural aspects of megasporogenesis in Lilium, Allium and Impatiens
    Boer-de Jeu, M.J. de - \ 1978
    Landbouwhogeschool Wageningen. Promotor(en): J.L. van Went, co-promotor(en): M.T.M. Willemse. - Wageningen : Veenman - 128
    liliaceae - alliaceae - allium - balsaminaceae - impatiens - embryozak - sierplanten - liliaceae - alliaceae - allium - balsaminaceae - impatiens - embryo sac - ornamental plants
    In higher plants the development of the female gametophyte - the embryo sac - involves two subsequent processes: megasporogenesis and megagameto genesis. Megasporogenesis is the process during which one functional mega spore is formed by meiosis of one particular nucellus cell. This functional mega spore can contain one, two or four haploid nuclei (respectively following the mono-, bi- or tetrasporic developmental type) depending on the circumstance whether a cell-wall is formed after the first and/or the second meiotic division or not. Additional megaspores, when formed, degenerate during megasporo genesis. The functional megaspore develops into the embryosac after a number of mitotic divisions. This process is called megagametogenesis. The cell in volved is called megasporocyte or megaspore mother-cell during megasporo genesis and forms a megagametophyte during megagametogenesis.

    In this thesis the ultrastructural aspects of megasporogenesis have been studied with the employ of electron-microscopic technics. Initially we intended to study the megasporogenesis in three species, each representing one of the three types mentioned above. For this purpose the species Impatiens walleriana Hook. f, Allium cepa L. and the Lilium hybrid 'Enchantment', were chosen which, according to other investigators respectively would show the mono-, bi- and tetrasporic types of development. However, our observations revealed a bisporic type of development for Impatiens as well, so that eventually two species having the bisporic type and one species having the tetrasporic type were examined.

    During our investigation the ultrastructural changes and the localization of the various cell organelles in the different developmental stages were observed. At the same time quantitative data concerning the number of the various cell organelles were collected during the whole of the developmental process. See enclosures I, II, III, IV and V.

    In the chapters 3, 4 and 5 the ultrastructural aspects of megasporogenesis respectively of Lilium, Allium and Impatiens are described and discussed separately. From the results we can conclude that each species shows its specific ultrastructural aspects during megasporogenesis. Lilium shows a very specific formation of an extensive endoplasmic reticulum, whereas in Allium the dictyosomes show a typical ultrastructure and localization. Impatiens shows an increasing amount of starch granules in the plastids, which is not found in the other two species.

    The differences and similarities in the ultrastructural changes of the cell organelles found in the three species are discussed more in detail per cell organelle in chapter 6. In chapter 7 a classification is given of these similarities and differences in different groups. Some of the similarities in the ultrastructural aspects of megasporogenesis between the three species examined seem to be specific for the process of meiosis, because of a known or presumed functional relation to this process. The other similarities and all the differences are specific for the process of megasporogenesis. The differences can be distinguished in species- specific and (developmental) type-specific characteristics.

    The similarities in the ultrastructural aspects of the three species, which are related to the process of meiosis, are in the first place found in the development of the nuclear chromatin and of the microtubules. The chromatin structure in the nucleus of each species shows similar ultrastructural changes, owing to the different developmental stages. The microtubules have a function in the spindle figure. Secondly, the ultrastructural changes of the nuclear envelope, the nucleolus, the nucleolus-like bodies in the cytoplasm and the cytoplasmic ribosomes show similarities between the three species examined. The undulations of the nuclear envelope, probably caused by a synthesis of new nuclear membrane before nuclear division and the sacculation of the inner nuclear membrane are probably related to a nucleo-cytoplasmic exchange of information, which takes place from nucleus to cytoplasm or vice versa during meiosis. The decrease of the number of ribosomes per cytoplasmic area during meiotic prophase is related to a low number of nuclear pores and an increase in volume of the nucleolus at this stage; the increase of the number of ribosomes per cytoplasmic area after metaphase I is related to the disintegration of the nuclear envelope before metaphase I and the presence of nucleolus-like bodies in the cytoplasm after metaphase I.

    Some similarities related to the process of megasporogenesis are the position of the developing megasporocyte in the nucellus, the localization of the plasmodesmata in the cell-wall and the storage of reserve-food in the cell. The developmental changes of the mitochondria, the plastids and the appearance of the central vacuole are related to both megasporogenesis and megagametogenesis. During megasporogenesis the developing megaspore mother-cell is surrounded by nucellus cells and is dependent on these cells for its nutrientsupply. There seems to be an interaction between the nucellus cells and the developing megaspore mother-cell, as a result of which the development of the megaspore mother-cell is influenced by the nucellus. A direct contact between the megaspore mother-cell and the nucellus cells is found only on the chalazal side of the megaspore mother- cell, where plasmodesmata are found in all three species examined. On the chalazal side of the nucellar tissue the vascular bundle ends and from this side a nutrient transport to the megaspore mother-cell takes place, causing a nutrient-gradient in the cell. This nutrient-gradient may define the polar distribution of some cell organelles in the cell. In the megasporocyte a storage of reserve-food takes place. The degree of heterotrophy of the megasporocyte can be determined by this storage of reserve-food and seems to be species-specific. During megasporogenesis the mitochondria and the plastids show ultrastructural changes, whereas they return to their original ultrastructure during megagametogenesis. The formation of a central vacuole during megagametogenesis is also related to the presence of small vacuoles during megasporogenesis.

    Apart from these general characteristics of the process of megasporogenesis we can distinguish species-specific and type-specific characteristics of the process. The species-specific characteristics are specific differences in the contact with the chalazal neighbour nucellus cells and in the reaction of the nucellus cells on the presence of the megasporocyte and the developing megagametophyte. The mitochondria and the plastids show specific ultrastructures, whereas the storage of reserve-food in the formation of starch and lipid bodies seem to be speciesspecific. The type-specific characteristics are concerned with the classification of the process in the bi- and tetrasporic types of development. The ultrastructural changes of the dictyosomes and of the endoplasmic reticulum, the polar localization of some cell organelles and the degeneration of the non-functional cell are specific characteristics related to the type of megasporogenesis.

    Bevruchting
    Sneep, J. - \ 1975
    Wageningen : LH, Plantenveredeling - 54
    bevruchting - bestuiving - plantenembryo's - voortplanting - embryozak - bedektzadigen - fertilization - pollination - plant embryos - reproduction - embryo sac - angiosperms
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