Role of cytoskeleton in plants reproduction

This review concerns the role of cytoskeletal elements: microtubules and microfilaments in plants reproduction brought to light by recent electron microscopic and immunofluorescence investigations on mitotic and meiotic cells, as well as on the development of male and female gametophytes. Configurations of the cytoskeleton depend on the cell cycle phase and on morphogenetic processes. The mitotic cell cycle contains five configurations of cytoskeletal fibers: cortical network, preprophase band, mitotic spindle and perinuclear radial arrangement. The cortical network exists at the stages G1, S and G2 but at the end of the G2 the preprophase band exists as a peculiar form of cortical microtubules, predicting the future division plane. The cytoskeleton of meiotic cells doesn´t contain the preprophase band configuration. In anthers, themicrosporocytes (the male line of generative cells) are divided into tetrads after successive or simultaneous cytokinesis. There are quite dense arrangements of microtubules and microfilaments in cytoplasm of prophasemicrosporocyte and two other configurations of the cytoskeleton; meiotic spindle and phragmoplast in the metaphase I and telophase I cytoskeleton. Such configurations are doubled in metaphase II and telophase II. The phragmoplast is arranged between sister and non sister nuclei in case of simultaneous cytokinesis, while in two separate bipolar phragmoplasts in case of successive cytokinesis. Before the first mitosis in the microspores an asymmetric microtubular cytoskleleton is developed, resulting in displacement of the nucleus to the cell periphery. Later the first, asymmetric, haploid mitosis forms a much bigger vegetative cell and a smaller generative one. The generative cell changes in the shape from a lens to spherical and to a spindle shape. This cell divides (in pollen grain or in pollen tube) forming two male gametes. The development of female line of generative cells starts in hypodermal cell at the micropylar end of the ovule. The megasporocyte performs random or perinuclear disposition of cytoskeletal elements in mitotic prophase with a temporary concentration during nucleus migration. During the meiosis the tetrad of megaspores is formedwith the linear or T shape arrangement. Finally the haploid embryo sac develops with a peculiar cytoskeletal organisation. The pollen tube and gametes entrance is an effect of interaction of the actin cytoskeleton and myosin (or a myosin like protein) on the surface of male gametes

Female gametophyte and pollen tube of Epilobium palustre L.

The monosporic, tetranucleate embryo sac of Epilobium palustre (Onagraceae) develops from the micropylar megaspore in a linear tetrad. In mononucleate embryo sacs a peculiar chromatic structure associated with a nucleolus appears in the nucleus. This structure seems to be formed by fibrillar material and is not visible in the subsequant stages of development. A large amount of rough ER cisternae occurs in the late mononucleate stage, during the binucleate stage their contents become optically dense. It the early tetranucleate stage the amount of ER is small, it increases again in the developing synergids and central cell. Numerous amyloplasts present in the mononucleate embryo sac loose their starch grains and some are transformed into cup-shaped plastids or proplastids. They are passed on to each of the embryo sac cells. The growth of the pollen tube ceases immediately after the penetration through the filiform apparatus of a synergid. At the apex of the tube a pore is formed. At the last stages of the penetration the apical part of the pollen tube becomes separated by a transverse partition from the distal part of the tube. The contents of the both parts differ in their internal structure. The distal part contains cytoplasm with numerous organoids, while the apical part is mainly filled with spherical bodies

Female gametophyte and pollen tube of Epilobium palustre L.

The monosporic, tetranucleate embryo sac of Epilobium palustre (Onagraceae) develops from the micropylar megaspore in a linear tetrad. In mononucleate embryo sacs a peculiar chromatic structure associated with a nucleolus appears in the nucleus. This structure seems to be formed by fibrillar material and is not visible in the subsequant stages of development. A large amount of rough ER cisternae occurs in the late mononucleate stage, during the binucleate stage their contents become optically dense. It the early tetranucleate stage the amount of ER is small, it increases again in the developing synergids and central cell. Numerous amyloplasts present in the mononucleate embryo sac loose their starch grains and some are transformed into cup-shaped plastids or proplastids. They are passed on to each of the embryo sac cells. The growth of the pollen tube ceases immediately after the penetration through the filiform apparatus of a synergid. At the apex of the tube a pore is formed. At the last stages of the penetration the apical part of the pollen tube becomes separated by a transverse partition from the distal part of the tube. The contents of the both parts differ in their internal structure. The distal part contains cytoplasm with numerous organoids, while the apical part is mainly filled with spherical bodies

Ultrastructural changes during megasporogenesis in Epipactis (Orchidaceae)

Plastids were temporarily localized within the micropylar portion of the early first prophase Epipactis meiocyte. Some of these plastids were observed in close proximity to the nuclear envelope. With the exception of this short period plastids were distributed randomly in the meiocyte. During late prophase, starch-containing plastids become cup-shaped and depleted of starch. Plastids were found within both dyad cells and all cells of the tetrad. Elongated segments of ER cisternae in various configurations were present. The chalazal wall of the prophase meiocyte differed from other walls in the presence of the ingrowths and plasmodesmata. The micropylar portion of the nuclear envelope at some stages of the I prophase seemed to be devoid of pores whereas the chalazal part contained numerous pores. These structural characters reflect a polar differentiation of the meiocyte along a micropylar-chalazal axis

Budowa pylnika i ziarna pyłku Deschampsia antarctica Desv. w mikroskopie konfokalnym

The structure of the anther and pollen grain was investigated in an Antarctic plant Deschampsia antarctica Desv. under a confocal microscope (CLSM). The Antarctic hair grass is one of the two native vascular plants growing in Antarctica. The structure of D. antarctica stamens with their short filaments and elongated anthers is typical of the family Poaceae. Microsporogenesis and development of D. antarctica pollen grains proceeds in a way typical of angiosperms from the family Poaceae. Beside the pistil, the hermaphroditic flower has three stamens with numerous pollen grains in pollen loculi. The monoporate and heteropolar pollen grains have a porus located at the distal pole. When observed under the confocal microscope (CLSM), D. antarctica microspores and pollen grains packed tightly inside the microsporangium exhibit strong fluorescence after eosin staining (green fluorescence). The use of calcofluor yielded blue fluorescence of anther endothecial cell walls. The D. antarctica anther endothecium is formed of a single layer of cells, although more than one layer of cells were observed at some sites.Budowę pylnika i ziaren pyłku badano za pomocą mikroskopu konfokalnego (CLSM) u antarktycznej rośliny Deschampsia antarctica Desv. Śmiałek antarktyczny jest jedną z dwóch rodzimych roślin naczyniowych rosnących na Antarktydzie. Pręciki D. antarctica mają budowę typową dla rodziny Poaceae z krótką nitką i wydłużonymi pylnikami. Mikrosporogeneza i rozwój ziaren pyłku D. antarctica przebiega w sposób typowy dla roślin okrytozalążkowych z rodziny Poaceae. W hermafrodytycznym kwiecie obok słupka występują trzy pręciki, z licznymi ziarnami pyłku w komorach pyłkowych. Ziarna pyłku są jednoporowe i różnobiegunowe, z porusem położonym na biegunie dystalnym. Mikrospory i ziarna pyłku u D. antarctica ułożone ściśle wewnątrz mikrosporangium, obserwowane w mikroskopie konfokalnym (CLSM) wykazują silną fluorescencję po zabarwieniu eozyną (zielona fluorescencja). Po zastosowaniu kalkafluoru ściany komórek endotecjum pylnika fluoryzują na niebiesko. Endotecjum pylnika D. antarctica zbudowane jest z jednej warstwy komórek; w niektórych miejscach obserwowano więcej niż jedną warstwę komórek

Structure of Deschampsia antarctica Desv. anther and pollen grain under the confocal microscope

The structure of the anther and pollen grain was investigated in an Antarctic plant Deschampsia antarctica Desv. under a confocal microscope (CLSM). The Antarctic hair grass is one of the two native vascular plants growing in Antarctica. The structure of D. antarctica stamens with their short filaments and elongated anthers is typical of the family Poaceae. Microsporogenesis and development of D. antarctica pollen grains proceeds in a way typical of angiosperms from the family Poaceae. Beside the pistil, the hermaphroditic flower has three stamens with numerous pollen grains in pollen loculi. The monoporate and heteropolar pollen grains have a porus located at the distal pole. When observed under the confocal microscope (CLSM), D. antarctica microspores and pollen grains packed tightly inside the microsporangium exhibit strong fluorescence after eosin staining (green fluorescence). The use of calcofluor yielded blue fluorescence of anther endothecial cell walls. The D. antarctica anther endothecium is formed of a single layer of cells, although more than one layer of cells were observed at some sites.Budowę pylnika i ziaren pyłku badano za pomocą mikroskopu konfokalnego (CLSM) u antarktycznej rośliny Deschampsia antarctica Desv. Śmiałek antarktyczny jest jedną z dwóch rodzimych roślin naczyniowych rosnących na Antarktydzie. Pręciki D. antarctica mają budowę typową dla rodziny Poaceae z krótką nitką i wydłużonymi pylnikami. Mikrosporogeneza i rozwój ziaren pyłku D. antarctica przebiega w sposób typowy dla roślin okrytozalążkowych z rodziny Poaceae. W hermafrodytycznym kwiecie obok słupka występują trzy pręciki, z licznymi ziarnami pyłku w komorach pyłkowych. Ziarna pyłku są jednoporowe i różnobiegunowe, z porusem położonym na biegunie dystalnym. Mikrospory i ziarna pyłku u D. antarctica ułożone ściśle wewnątrz mikrosporangium, obserwowane w mikroskopie konfokalnym (CLSM) wykazują silną fluorescencję po zabarwieniu eozyną (zielona fluorescencja). Po zastosowaniu kalkafluoru ściany komórek endotecjum pylnika fluoryzują na niebiesko. Endotecjum pylnika D. antarctica zbudowane jest z jednej warstwy komórek; w niektórych miejscach obserwowano więcej niż jedną warstwę komórek