Early embryogenesis in Arabidopsis thaliana. II. The developing embryo

1991 ◽  
Vol 69 (3) ◽  
pp. 461-476 ◽  
Author(s):  
S. G. Mansfield ◽  
L. G. Briarty
Keyword(s):  
Arabidopsis Thaliana ◽  
Embryo Sac ◽  
Early Embryogenesis ◽  
Total Cell ◽  
Filiform Apparatus ◽  
Globular Stage ◽  
Original Length ◽  
Total Cell Volume ◽  
End Wall ◽  
Arabidopsis Embryogenesis

Embryo differentiation in Arabidopsis thaliana follows the classical Capsella variation of the Onagrad type. Fertilization occurs approximately 3 h after flowering, whereupon vacuolar organization in the zygote changes and the cell elongates rapidly to approximately three times its original length. Cytoplasmic polarization is maintained. During the first two division steps there is very little increase in total cell volume, and during subsequent divisions vacuole number increases, with a concomitant decrease in size. Plastids remain undifferentiated up to the late globular stage, after which grana begin to develop. Ribosomal concentration increases significantly after fertilization. Differences between embryo proper cells become evident by the heart stage; vacuole, plastid, and mitochondrial abundance, size, and complexity vary within the embryo. There are no plasmodesmatal connections with the endosperm or integuments. Suspensor development is complete by the early globular stage, when it consists of seven to nine highly vacuolate cells, each linked by end wall plasmodesmata. Ribosome and volume densities of plastids and mitochondria are significantly lower than in the embryo proper organelles, and dictyosomes are infrequent. Embryo sac wall projections proliferate throughout the micropylar chamber, especially adjacent to the filiform apparatus and zygote base, and ingrowths form on the basal cell proximal wall. Key words: Arabidopsis, embryogenesis, embryo differentiation, wall ingrowths.

Capsella Embryogenesis: the Chalazal Proliferating Tissue

1971 ◽  
Vol 8 (1) ◽  
pp. 201-227
Author(s):  
PATRICIA SCHULZ ◽  
W. A. JENSEN
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Embryo Sac ◽  
Proximal Part ◽  
Ultrastructural Changes ◽  
Multivesicular Bodies ◽  
Proliferating Cells ◽  
Globular Stage ◽  
End Wall ◽  
Histochemical Changes

Electron-microscope and histochemical procedures were used to study the development and breakdown of the chalazal proliferating tissue in Capsella. This tissue is formed by the enlargement of several layers of nucellar cells at the chalazal end of the embryo sac. When the embryo reaches the early globular stage these enlarged cells start to disintegrate, beginning with those immediately bordering the embryo sac and continuing until all have broken down. Characteristic ultrastructural changes accompany the development and breakdown of the chalazal proliferating cells. The mature cells form increased numbers of dictyosomes and large amounts of endoplasmic reticulum (ER). This is accompanied by a thickening of the cell wall. As the cells begin to break down, electron density increases, plastids become polarized in the cells, dictyosomes disappear and the ER is dispersed and fragmented. Plastids, some mitochondria, and pieces of ER appear to be digested in autophagic vacuoles. Cell disorganization is accompanied by an increased number of microbodies and multivesicular bodies per cell. Finally, the nucleus breaks down and the plasmalemma disappears. The end wall ruptures and releases intact mitochondria, ribosomes, and portions of degenerated cytoplasm into the endosperm. Histochemical changes accompany these events. Also discussed are the antipodals and the destruction of the proximal part of the chalazal nucellus by the expanding megagametophyte prior to the development of the chalazal proliferating tissue.

Needle microepiphytes in a Douglas fir canopy: biomass and distribution patterns

1979 ◽  
Vol 57 (9) ◽  
pp. 1000-1007 ◽  
Author(s):  
George C. Carroll
Keyword(s):  
Cell Volume ◽  
Distribution Patterns ◽  
Douglas Fir ◽  
Total Cell ◽  
Microbial Cell ◽  
Microbial Cells ◽  
Cutting Out ◽  
Total Cell Volume ◽  
Volume Estimates ◽  
Cell Volumes

Distribution patterns and total cell-volume estimates for needle microepiphytes are presented for three strata in the canopy of a single old-growth Douglas fir tree. Microbial cell volume was estimated by photographing transverse sections of needles, tracing microbial profiles on Mylar film, cutting out the tracings, and determining the pooled trace weights from various zones of each needle section. Microbial cells are concentrated in the midrib groove and over the stomatal zones of individual needles. Microbial cell volume on the upper needle surfaces increases during the 1st year and declines in subsequent years. Cell volumes on the lower needle surfaces increase from the 1st to the 3rd year and decrease from the 3rd to the 4th year. An increase in microbial cell volume occurs on both upper and lower surfaces from year 7 to year 8. Total microbial cell volume in relation to available needle surface area is greatest in the lower canopy and decreases with increasing height in the canopy. The total volume of microbial cells on needles was estimated to be 1093 cm3 for the entire tree.

Development of a Heat-Inducible Gene Expression System Using Female Gametophytes of Arabidopsis thaliana

2019 ◽  
Vol 60 (11) ◽  
pp. 2564-2572 ◽  
Author(s):  
Dukhyun Hwang ◽  
Satomi Wada ◽  
Azusa Takahashi ◽  
Hiroko Urawa ◽  
Yasuhiro Kamei ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Expression System ◽  
Embryo Sac ◽  
Gene Induction ◽  
Central Cell ◽  
Egg Cell ◽  
Dominant Negative Mutant ◽  
Nucleate Cell ◽  
Recombination System ◽  
Induction System

Abstract Female gametophyte (FG) is crucial for reproduction in flowering plants. Arabidopsis thaliana produces Polygonum-type FGs, which consist of an egg cell, two synergid cells, three antipodal cells and a central cell. Egg cell and central cell are the two female gametes that give rise to the embryo and surrounding endosperm, respectively, after fertilization. During the development of a FG, a single megaspore produced by meiosis undergoes three rounds of mitosis to produce an eight-nucleate cell. A seven-celled FG is formed after cellularization. The central cell initially contains two polar nuclei that fuse during female gametogenesis to form the secondary nucleus. In this study, we developed a gene induction system for analyzing the functions of various genes in developing Arabidopsis FGs. This system allows transgene expression in developing FGs using the heat-inducible Cre-loxP recombination system and FG-specific embryo sac 2 (ES2) promoter. Efficient gene induction was achieved in FGs by incubating flower buds and isolated pistils at 35�C for short periods of time (1–5 min). Gene induction was also induced in developing FGs by heat treatment of isolated ovules using the infrared laser-evoked gene operator (IR-LEGO) system. Expression of a dominant-negative mutant of Sad1/UNC84 (SUN) proteins in developing FGs using the gene induction system developed in this study caused defects in polar nuclear fusion, indicating the roles of SUN proteins in this process. This strategy represents a new tool for analyzing the functions of genes in FG development and FG functions.

Apomixis and abnormal anther development in Calotis lappulacea Benth. (Compositae)

1968 ◽  
Vol 16 (1) ◽  
pp. 1 ◽  
Author(s):  
GL Davis
Keyword(s):  
New South ◽  
Embryo Sac ◽  
Pollen Grains ◽  
Anther Wall ◽  
Male Gametes ◽  
Globular Stage ◽  
South Wales ◽  
Vertical Division ◽  
Endosperm Formation ◽  
Embryo Sac Formation

A comparative study was made of material collected from four localities in New South Wales and Queensland and a number of embryological aberrations were found to be common to all districts. During microsporogenesis, certain tapetal cells not only failed to contribute to the tapetal periplasmodium but, after increasing in size, they separated from the anther wall and resembled one-, two-, or four-nucleate embryo sacs developing among the microspores. In one anther a structure was present which was very similar to a fully differentiated embryo sac. Although the pollen grains of some anthers contained male gametes, most anthers dehisced when the pollen was two-celled and some shrivelled soon after meiosis. Megasporogenesis was followed by the formation of linear tetrads of megaspores, but embryo sac formation was the result of somatic apospory and C. lappulacea appears to be an obligate apomict. The enlarging somatic cell usually invades the nucellar lobe and replaces the megaspores but one or more such celis commonly develop also in the chalaza, and up to eight embryo sacs were found in one ovule. Enlargement of a chalazal embryo sac sometimes resulted in penetration of the ovular epidermis and its invasion of the loculus as a haustorium-like structure. Extrusion of a developing embryo sac through the micropyle was common. Embryogeny is of the Asterad type, but vertical division of the terminal cell ca was delayed until after the basal cell cb had given rise to superposed cells m and ci. Polyembryony was common but only one embryo in each ovule reached maturity. Endosperm formation was independent of embryogeny but unless it was initiated before the globular stage of the embryo, the embryo sac collapsed and the embryo degenerated.

A 400-year-old Douglas fir tree and its epiphytes: biomass, surface area, and their distributions

1977 ◽  
Vol 7 (4) ◽  
pp. 680-699 ◽  
Author(s):  
Lawrence H. Pike ◽  
Robert A. Rydell ◽  
William C. Denison
Keyword(s):  
Internal Structure ◽  
Surface Area ◽  
Douglas Fir ◽  
Total Cell ◽  
Mountain Climbing ◽  
Vertical Distributions ◽  
Total Cell Volume ◽  
Horizontal And Vertical Distributions ◽  
Two Stages ◽  
Total Tree

Methods have been developed to yield total tree estimates of biomass for various components of a tree (trunk, axes, twigs, and needles) and its community of epiphytes (microorganisms, lichens, and bryophytes). Trees were sampled with the help of climbing techniques modified from mountain climbing. Two stages of sampling were involved. First, all units of the population were described so that their weights could be predicted. Second, several units were chosen with probability of selection dependent upon predicted weight and sampled in detail. Biomass estimates from the sampled units were expanded to tree totals with information gathered during the first sampling stage. Internal structure of the crown (tree components and epiphytes) is illustrated by maps of trunk and branch systems and by diagrams of horizontal and vertical distributions. This internal structure was also derived from the first sampling stage.These methods have been applied to nine old-growth Douglas fir trees (Pseudotsugamenziesii (Mirb.) Franco). Data from a single 400-year-old tree (1.46 m dbh, 77 m in height) in the H. J. Andrews Experimental Forest in the western Cascade Mountains of Oregon are presented. Biomass and surface area estimates are as follows: trunk, 26 870 kg, 223 m2; axes (>4 cm), 1530 kg, 81 m2; living twigs (<4 cm), 480 kg, 373 m2; dead twigs, 78 kg, 104 m2; needles, 198 kg, 2860 m2; lichens, 13.1 kg; and bryophytes, 4.7 kg. Total cell volume of microepiphytes on twigs was estimated to have been 300 cm3 and total cover by microepiphytes on needles was estimated to have been 191 m2.

The development of the embryo sac of sunflower Helianthus annuus after fertilization

1973 ◽  
Vol 51 (5) ◽  
pp. 879-890 ◽  
Author(s):  
William Newcomb
Keyword(s):  
Helianthus Annuus ◽  
Mitotic Spindle ◽  
Embryo Sac ◽  
Endosperm Development ◽  
Primary Endosperm Nucleus ◽  
Single Row ◽  
Wall Formation ◽  
Globular Stage ◽  
Spindle Apparatus ◽  
Single Fertilization

The degeneration of one synergid denotes the initiation of embryo and endosperm development in the embryo sac of sunflower Helianthus annuus L. The other synergid, the persistent synergid, is present until the late globular stage of embryogenesis. The primary endosperm nucleus divides before the zygote nucleus forming a coenocytic nuclear endosperm. When about eight endosperm nuclei are present during the early globular stage of embryogenesis, endosperm wall formation starts at the micropylar end of the embryo sac. The walls continue to grow toward the chalazal end of the embryo sac apparently as a result of the activity of Golgi located at the tips of the growing walls. Most endosperm wall formation is not associated with a mitotic spindle apparatus in sunflower. The suspensor of the embryo consists of a large basal cell during the proembryo stages, a single row of cells during the early globular stages, and at the late globular stage a double tier of cells near the radicle end of the embryo and a single row at the micropylar end of the embryo sac. Occasionally embryo development occurs in the absence of endosperm when only single fertilization has taken place. The development and nutritional implications of post-fertilization events in the sunflower embryo sac are discussed.

scholarly journals Cellular dimensions affecting the nucleocytoplasmic volume ratio.

1991 ◽  
Vol 115 (4) ◽  
pp. 941-948 ◽  
Author(s):  
J A Swanson ◽  
M Lee ◽  
P E Knapp
Keyword(s):  
Endothelial Cells ◽  
Cell Volume ◽  
Volume Ratio ◽  
Fluorescein Isothiocyanate ◽  
Total Cell ◽  
Nuclear Volume ◽  
Size Exclusion ◽  
Nuclear Surface ◽  
Murine Bone Marrow ◽  
Total Cell Volume

Although it has long been appreciated that larger eukaryotic cells have larger nuclei, little is known about how this size relationship is maintained. Here we describe a method for measuring the aqueous volume ratio of nucleus to cytoplasm, two compartments which are interconnected via the pores in the nuclear envelope. We then use that method to identify proportional cellular dimensions in variously treated cells and in different cell types. Cells were scrape loaded with a mixture of fluorescent dextrans: Texas red dextran, average mol wt = 10,000 (TRDx10), and fluorescein isothiocyanate dextran, average mol wt = 70,000 (FDx70). After introduction into the cytoplasmic space, the TRDx10 distributed into both the nucleus and cytoplasm, whereas the FDx70 was restricted to cytoplasm, due to size exclusion by the nuclear pores. The aqueous nucleocytoplasmic volume ratio (RN/C) was determined by measuring, from fluorescence images of spread cells, total cellular fluorescence of each of the two probes and the fluorescence ratio of those probes in the cytoplasm. RN/C was unaffected by the measurement procedure or by varying temperatures between 23 degrees and 37 degrees C. Loading excess unlabeled dextrans had little effect on RN/C, with the single exception that high concentrations of large dextrans could lower RN/C in endothelial cells. Expanding intracellular membranous compartments of macrophages by phagocytosis of latex beads decreased RN/C. Expanding the same compartment by pinocytosis of sucrose, which nearly doubled total cell volume, had little effect on RN/C, indicating that nuclear volume was more closely linked to the cytoplasmic volume, exclusive of vesicular organelles, than to total cell volume. RN/C was the same in mononucleate and binucleate endothelial cells. Finally, measurements of RN/C in murine bone marrow-derived macrophages, bovine aortic endothelial cells, Swiss 3T3 fibroblasts, PtK2 cells, and CV-1 cells revealed that nuclear volume scaled allometrically with cell volume. The allometric relationship indicated that cell volume was proportional to nuclear surface area.

scholarly journals Arabidopsis thaliana natural variation in temperature-modulated immunity uncovers transcription factor UNE12 as a thermoresponsive regulator

2019 ◽  
Author(s):  
Friederike Bruessow ◽  
Jaqueline Bautor ◽  
Gesa Hoffmann ◽  
Jane E. Parker
Keyword(s):  
Arabidopsis Thaliana ◽  
Transcription Factor ◽  
Plant Immunity ◽  
Embryo Sac ◽  
Bacterial Pathogen ◽  
Plant Responses ◽  
Stress Hormone ◽  
Negative Effects ◽  
Over Expression ◽  
Temperature Impacts

AbstractTemperature impacts plant immunity and growth but how temperature intersects with endogenous pathways remains unclear. Here we uncover variation between Arabidopsis thaliana natural accessions in response to two non-stress temperatures (22°C and 16°C) affecting accumulation of the thermoresponsive stress hormone salicylic acid (SA) and plant growth. Analysis of differentially responding A. thaliana accessions shows that pre-existing SA provides a benefit in limiting bacterial pathogen infection at both temperatures. Several A. thaliana genotypes display a capacity to mitigate negative effects of high SA on growth, indicating within-species plasticity in SA - growth tradeoffs. An association study of temperature x SA variation, followed by physiological and immunity phenotyping of mutant and over-expression lines, identifies the transcription factor unfertilized embryo sac 12 (UNE12) as a temperature-responsive SA immunity regulator. Here we reveal previously untapped diversity in plant responses to temperature and a way forward in understanding the genetic architecture of plant adaptation to changing environments.

scholarly journals BLOOD DESTRUCTION DURING EXERCISE

1922 ◽  
Vol 36 (5) ◽  
pp. 481-500 ◽  
Author(s):  
G. O. Broun
Keyword(s):  
Cell Volume ◽  
Plasma Volume ◽  
Peripheral Blood ◽  
Prolonged Exercise ◽  
Jugular Vein ◽  
Total Cell ◽  
Total Cell Volume

The following changes have been demonstrated to take place in the blood of dogs during exercise. 1. An increase in the per cent of cells and hemoglobin in the blood of the jugular vein occurs early in the course of exercise. It probably results from a redistribution of red corpuscles, with an increase in their proportion in the peripheral blood. 2. As exercise is continued, there is a definite increase in plasma volume. 3. A coincident decrease both in the total cell volume and the pigment volume during prolonged exercise suggests that blood destruction then occurs.

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