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Keith R Slotkin - One of the best experts on this subject based on the ideXlab platform.
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cytoplasmic connection of sperm cells to the Pollen vegetative cell nucleus potential roles of the male germ unit revisited
Journal of Experimental Botany, 2011Co-Authors: Andrea D Mccue, M Cresti, Jose A Feijo, Keith R SlotkinAbstract:The male germ cells of angiosperm plants are neither free-living nor flagellated and therefore are dependent on the unique structure of the Pollen Grain for fertilization. During angiosperm male gametogenesis, an asymmetric mitotic division produces the generative cell, which is completely enclosed within the cytoplasm of the larger Pollen Grain vegetative cell. Mitotic division of the generative cell generates two sperm cells that remain connected by a common extracellular matrix with potential intercellular connections. In addition, one sperm cell has a cytoplasmic projection in contact with the vegetative cell nucleus. The shared extracellular matrix of the two sperm cells and the physical association of one sperm cell to the vegetative cell nucleus forms a linkage of all the genetic material in the Pollen Grain, termed the male germ unit. Found in species representing both the monocot and eudicot lineages, the cytoplasmic projection is formed by vesicle formation and microtubule elongation shortly after the formation of the generative cell and tethers the male germ unit until just prior to fertilization. The cytoplasmic projection plays a structural role in linking the male germ unit, but potentially plays other important roles. Recently, it has been speculated that the cytoplasmic projection and the male germ unit may facilitate communication between the somatic vegetative cell nucleus and the germinal sperm cells, via RNA and/or protein transport. This review focuses on the nature of the sperm cell cytoplasmic projection and the potential communicative function of the male germ unit.
Jose A Feijo - One of the best experts on this subject based on the ideXlab platform.
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cytoplasmic connection of sperm cells to the Pollen vegetative cell nucleus potential roles of the male germ unit revisited
Journal of Experimental Botany, 2011Co-Authors: Andrea D Mccue, M Cresti, Jose A Feijo, Keith R SlotkinAbstract:The male germ cells of angiosperm plants are neither free-living nor flagellated and therefore are dependent on the unique structure of the Pollen Grain for fertilization. During angiosperm male gametogenesis, an asymmetric mitotic division produces the generative cell, which is completely enclosed within the cytoplasm of the larger Pollen Grain vegetative cell. Mitotic division of the generative cell generates two sperm cells that remain connected by a common extracellular matrix with potential intercellular connections. In addition, one sperm cell has a cytoplasmic projection in contact with the vegetative cell nucleus. The shared extracellular matrix of the two sperm cells and the physical association of one sperm cell to the vegetative cell nucleus forms a linkage of all the genetic material in the Pollen Grain, termed the male germ unit. Found in species representing both the monocot and eudicot lineages, the cytoplasmic projection is formed by vesicle formation and microtubule elongation shortly after the formation of the generative cell and tethers the male germ unit until just prior to fertilization. The cytoplasmic projection plays a structural role in linking the male germ unit, but potentially plays other important roles. Recently, it has been speculated that the cytoplasmic projection and the male germ unit may facilitate communication between the somatic vegetative cell nucleus and the germinal sperm cells, via RNA and/or protein transport. This review focuses on the nature of the sperm cell cytoplasmic projection and the potential communicative function of the male germ unit.
Andrea D Mccue - One of the best experts on this subject based on the ideXlab platform.
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cytoplasmic connection of sperm cells to the Pollen vegetative cell nucleus potential roles of the male germ unit revisited
Journal of Experimental Botany, 2011Co-Authors: Andrea D Mccue, M Cresti, Jose A Feijo, Keith R SlotkinAbstract:The male germ cells of angiosperm plants are neither free-living nor flagellated and therefore are dependent on the unique structure of the Pollen Grain for fertilization. During angiosperm male gametogenesis, an asymmetric mitotic division produces the generative cell, which is completely enclosed within the cytoplasm of the larger Pollen Grain vegetative cell. Mitotic division of the generative cell generates two sperm cells that remain connected by a common extracellular matrix with potential intercellular connections. In addition, one sperm cell has a cytoplasmic projection in contact with the vegetative cell nucleus. The shared extracellular matrix of the two sperm cells and the physical association of one sperm cell to the vegetative cell nucleus forms a linkage of all the genetic material in the Pollen Grain, termed the male germ unit. Found in species representing both the monocot and eudicot lineages, the cytoplasmic projection is formed by vesicle formation and microtubule elongation shortly after the formation of the generative cell and tethers the male germ unit until just prior to fertilization. The cytoplasmic projection plays a structural role in linking the male germ unit, but potentially plays other important roles. Recently, it has been speculated that the cytoplasmic projection and the male germ unit may facilitate communication between the somatic vegetative cell nucleus and the germinal sperm cells, via RNA and/or protein transport. This review focuses on the nature of the sperm cell cytoplasmic projection and the potential communicative function of the male germ unit.
Tsuneyoshi Kuroiwa - One of the best experts on this subject based on the ideXlab platform.
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unequal distribution of dna containing organelles in generative and sperm cells of erythrina crista galli fabaceae
Sexual Plant Reproduction, 2000Co-Authors: Chieko Saito, Kimie Mori, Noriko Nagata, Atsushi Sakai, Haruko Kuroiwa, Tsuneyoshi KuroiwaAbstract:The generative cell at anthesis in the mature Pollen Grain of Erythrina crista-galli (Fabaceae) was examined by 4,6-diamidino-2-phenylindole(DAPI)-fluorescence microscopy using the squash method. An unequal, polarized distribution of DNA-containing organelles (plastids and/or mitochondria) within the generative cell was observed in every mature Pollen Grain examined. Polarization of DNA-containing organelles is obvious when generative cells are freed and assume a spherical shape soon after microspore mitosis, as revealed by fluorescence-microscopic observations of specimens embedded in Technovit 7100 resin and thin-sectioned at different developmental stages. Early establishment of polarized localization of organelles in young generative cells of E. crista-galli and maintenance of this unequal distribution until Pollen maturation strongly suggests that the organelles may still be clustered at Pollen mitosis. Production of a dimorphic pair of sperm cells, as has been reported in Plumbagozeylanica, was observed in some Pollen tubes germinated in vitro. The differentiation of the two sperm cells is discussed in relation to possible preferential double fertilization in angiosperms.
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quantitative study of organelle nucleoids during the second Pollen Grain mitosis in oenothera biennis
Protoplasma, 1997Co-Authors: Haruko Kuroiwa, Noriko Nagata, X L Guan, Zhaohui Qian, H Liu, Tsuneyoshi KuroiwaAbstract:The behavior of organelle nucleoids in the generative cell was examined at the second (Pollen Grain) mitosis by epifluorescence microscopy after staining with 4′,6-diamidino-2-phenylindole (DAPI) inOenothera biennis. TheO. biennis generative cell contained a large number of organelle nucleoids distributed randomly in the cytoplasm before mitosis. The epifluorescence images of the nucleoids could be classified distinctly into two groups which corresponded to plastid nucleoids (pt-nucleoids) and mitochondrial nucleoids (mt-nucleoids). Discrimination between pt- and mt-nucleoids was carried out with the aid of DNA immunogold electron microscopy. At metaphase, both pt- and mt-nucleoids migrated to the pole regions of the generative cell. After mitosis, organelle nucleoids in both of the sperm cells scattered in the cytoplasm again. A quantitative examination of pt-nucleoids on 202 pairs of sperm cells showed that the leading sperm cell (Svn) contained 0–39 pt-nucleoids (19.0 ± 7.4) and the trailing sperm cell (Sua) contained 0–40 pt-nucleoids (15.4 ± 6.5). For mt-nucleoids, examination of 28 pairs of sperm cells showed that Svn contained 5–32 mt-nucleoids (14.5 ± 6.8) and Sua contained 6–30 mt-nucleoids (13.4 ±7.5). These results showed that (1) the number of organelle nucleoids per sperm cell varied considerably in the cells studied; (2) quantitative difference in pt- and mt-nucleoids between Svn and Sua could occur in some gametophytes studied; but (3) it was unlikely that there was any pre-differentiational cytoplasm localization and essential sperm heteromorphy with respect to organelle nucleoid content in the gametophyte population.
David Twell - One of the best experts on this subject based on the ideXlab platform.
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small rna pathways are present and functional in the angiosperm male gametophyte
Molecular Plant, 2009Co-Authors: Robert Grantdownton, David Twell, Said Hafidh, H G DickinsonAbstract:Small non-coding RNAs are essential for development of the sporophyte, the somatic diploid phase of flowering plants. They are integral to key cellular processes such as defense, generation of chromatin structure, and regulation of native gene expression. Surprisingly, very little is known of their presence and function in the male haploid phase of plant development (male gametophyte/Pollen Grain), where dramatic cell fate changes leading to gametogenesis occur over just two mitotic divisions. We show that critical components of small RNA pathways are expressed throughout Pollen development, but in a pattern that differs from the sporophyte. We also demonstrate that mature Pollen accumulates a range of mature microRNAs, the class of small RNA most frequently involved in post-transcriptional regulation of endogenous gene expression. Significantly, these miRNAs cleave their target transcripts in developing Pollen—a process that seemingly contributes to the purging of key regulatory transcripts from the mature Pollen Grain. Small RNAs are thus likely to make a hitherto unappreciated contribution to male gametophyte gene expression patterns, Pollen development, and gametogenesis.
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genetic control of male germ unit organization in arabidopsis
Plant Physiology, 2002Co-Authors: Eric Lalanne, David TwellAbstract:In flowering plants, the vegetative nucleus and the two sperm cells are proposed to form a functional assemblage, the male germ unit (MGU). Here, we describe the developmental pathway of MGU assembly in Arabidopsis and report two classes of mutations that affect the integrity and/or the positioning of the MGU in the mature Pollen Grain. In germ unit malformed ( gum ) mutants, the vegetative nucleus is positioned adjacent to the Pollen Grain wall, separate from the two sperm cells, whereas in MGU displaced ( mud ) mutants, the intact MGU is displaced to the Pollen Grain wall. mud and gum mutants correspond to male-specific gametophytic mutations that also reduce Pollen fitness. Genetic mapping showed that the gum1 and gum2 mutations are genetically linked, possibly allelic, whereas the mud1 and mud2 mutations correspond to two unlinked loci mapping on different chromosomes. The hierarchical relationship between mud and gum mutations was investigated by phenotypic analysis of double mutants. gum1 appeared to act earlier than mud1 and mud2 , affecting initial MGU assembly and its stability during Pollen maturation. In contrast, mud1 and mud2 mutations appear to act only on MGU positioning during final maturation. From in planta analyses of Pollen germination in mud and gum mutants, we conclude that the initial proximity and positioning of MGU components is not required for their entrance into the Pollen tube, but the efficiency of MGU translocation is reduced.