The root endodermis in Ranunculus acris. I. Structure and ontogeny

1979 ◽  
Vol 57 (9) ◽  
pp. 1040-1062 ◽  
Author(s):  
M. G. Scott ◽  
R. L. Peterson
Keyword(s):  
Plasma Membrane ◽  
Early Stage ◽  
Cellulose Microfibrils ◽  
Secondary Development ◽  
Wall Material ◽  
Casparian Strip ◽  
Suberin Lamellae ◽  
Ranunculus Acris ◽  
Endodermal Cells ◽  
Root Endodermis

The root endodermis in Ranunculus acris was investigated using light and transmission electron microscopy to obtain a more complete picture of endodermal development in a dicotyledonous species. Following the formation of a lateral bulge in anticlinal walls of proendodermal cells, portions of the plasma membrane became tenaciously associated with the primary wall material. The plasma membrane in the zone of the Casparian band appeared extremely electron dense and displayed a distinct tripartite organization. Cytoplasm of primary stage endodermal cells contained Golgi bodies with associated vesicles, lipid-like droplets, and multivesicular bodies containing membrane-enclosed vesicles. Cellulose microfibrils in the radial walls of endodermal cells became impregnated with an osmiophilic substance possibly through the incorporation of paramural bodies at a ledge-like invagination of the plasma membrane on either side of the Casparian strip. It is proposed that the intense organelle activity in the vicinity of the Casparian strip could signify an early stage of suberin lamellae synthesis. Between 8 and 10 suberin lamellae were laid down on radial and tangential walls of those endodermal cells which underwent secondary development, with the heaviest deposition occurring in the region of the Casparian strip. The parallel orientation of the suberin lamellae was frequently disrupted by electron-dense 'platelets' and small granules. A fibrillar suberin-like material was found in dilated cisternae of endoplasmic reticulum located adjacent to areas of deposition. Nuclei, membranous configurations, mitochondria, plastids, and other cytoplasmic organelles were found to persist in tertiary stage endodermal cells. Histochemistry and SEM showed that the mature endodermal wall complex of field-grown plants was comprised of alternating bands of cellulose, lignin, and possibly, suberin.

The root endodermis in Ranunculus acris. II. Histochemistry of the endodermis and the synthesis of phenolic compounds in roots

1979 ◽  
Vol 57 (9) ◽  
pp. 1063-1077 ◽  
Author(s):  
M. G. Scott ◽  
R. L. Peterson
Keyword(s):  
Phenolic Compounds ◽  
Ultrastructural Level ◽  
Major Constituent ◽  
Hydroxyl Groups ◽  
Cortical Cells ◽  
Suberin Lamellae ◽  
Large Central Vacuole ◽  
Flocculent Material ◽  
Ranunculus Acris ◽  
Root Endodermis

Results of histochemical tests performed on fresh root tissue of Ranunculus acris provide the following information on the chemical nature of the root endodermis: (i) the Casparian strip is impregnated with lipid and possibly lignin, (ii) the suberin lamellae stain positively for lipid and phenols with free hydroxyl groups, and (iii) the tertiary wall contains alternating bands of lignin and cellulose.At the ultrastructural level, phenolic 'globules' present in vacuoles of adjacent cortical cells increase in size by accretion of flocculent material and the addition of dispersed granular material through the apparent fusion of smaller vacuoles with the large central vacuole. Globules adhering to fragments of the tonoplast membrane are clearly seen with the SEM.The ferric chloride test for catechol-type phenols at the TEM level proved useful in categorizing phenolic compounds present in intercellular spaces, in walls and vacuoles of cortical cells, surrounding starch grains in amyloplasts, and in the cytoplasm of endodermal cells. Prominent plastids containing large deposits of lipid, osmiophilic material, thylakoid membranes, and starch are seen to be a major constituent of cytoplasm in endodermal and cortical cells.

Exterior and Interior Events in Early Stage of Thrombin-induced Platelet Aggregation

1977 ◽  
Vol 38 (03) ◽  
pp. 0630-0639 ◽  
Author(s):  
Shuichi Hashimoto ◽  
Sachiko Shibata ◽  
Bonro Kobayashi
Keyword(s):  
Molecular Weight ◽  
Enzyme Activity ◽  
Plasma Membrane ◽  
Platelet Aggregation ◽  
Early Stage ◽  
Adenyl Cyclase ◽  
Cellular Component ◽  
Primary Event ◽  
Rabbit Platelets ◽  
Membrane Bound

SummaryTreatment of washed rabbit platelets with 1 u/ml of thrombin at 37° C resulted in a disappearance from platelets of a protein with 250,000 dalton molecular weight which was shown to be originated from plasma membrane. Parallel loss of adenyl cyclase was noted, and both reactions were complete within 30 sec. From the patterns of disc electrophoretograms, the importance of quick suppression of thrombin action in demonstrating the primary event was stressed.Thrombin induced an apparent activation of membrane bound phosphodiesterase. This reaction was also complete within 30 sec. The cellular component which contained the enzyme activity was distinct from plasma membrane. Soluble phosphodiesterase was not influenced by thrombin at all.These reactions required intact platelet cells to react with thrombin, and no reaction was detected when subcellular preparations were treated with thrombin.Possibility of collaboration of changes in externally located synthetic enzyme with those in internally located degrading enzyme in the early phase of thrombin action on platelets was suggested.

scholarly journals Two chemically distinct root lignin barriers control solute and water balance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Guilhem Reyt ◽  
Priya Ramakrishna ◽  
Isai Salas-González ◽  
Satoshi Fujita ◽  
Ashley Love ◽  
...  
Keyword(s):  
Critical Role ◽  
Phenylpropanoid Pathway ◽  
Cellular Functions ◽  
Casparian Strip ◽  
Transcriptional Reprogramming ◽  
Exogenous Cues ◽  
Endodermal Cells ◽  
Complex Polymer ◽  
Nutrient Homeostasis ◽  
Lignin Deposition

AbstractLignin is a complex polymer deposited in the cell wall of specialised plant cells, where it provides essential cellular functions. Plants coordinate timing, location, abundance and composition of lignin deposition in response to endogenous and exogenous cues. In roots, a fine band of lignin, the Casparian strip encircles endodermal cells. This forms an extracellular barrier to solutes and water and plays a critical role in maintaining nutrient homeostasis. A signalling pathway senses the integrity of this diffusion barrier and can induce over-lignification to compensate for barrier defects. Here, we report that activation of this endodermal sensing mechanism triggers a transcriptional reprogramming strongly inducing the phenylpropanoid pathway and immune signaling. This leads to deposition of compensatory lignin that is chemically distinct from Casparian strip lignin. We also report that a complete loss of endodermal lignification drastically impacts mineral nutrients homeostasis and plant growth.

scholarly journals The polymerization of actin: II. how nonfilamentous actin becomes nonrandomly distributed in sperm: evidence for the association of this actin with membranes

1976 ◽  
Vol 69 (1) ◽  
pp. 51-72 ◽  
Author(s):  
LG Tilney
Keyword(s):  
Plasma Membrane ◽  
Nuclear Envelope ◽  
Thin Section ◽  
Actin Filaments ◽  
Early Stage ◽  
Mature Sperm ◽  
Vacuole Membrane ◽  
Other Substances ◽  
Associated Proteins ◽  
Basal Half

At an early stage in spermiogenesis the acrosomal vacuole and other organelles including ribosomes are located at the basal end of the cell. From here actin must be transported to its future location at the anterior end of the cell. At no stage in the accumulation of actin in the periacrosomal region is the actin sequestered in a membrane-bounded compartment such as a vacuole or vesicle. Since filaments are not present in the periacrosomal region during the accumulation of the actin even though the fixation of these cells is sufficiently good to distinguish actin filaments in thin section, the actin must accumulate in the nonfilamentous state. The membranes in the periacrosomal region, specifically a portion of the nuclear envelope and the basal half of the acrosomal vacuole membrane, become specialized morphologically in advance of the accumulation of actin in this region. My working hypothesis is that the actin in combination with other substances binds to these specialized membranes and to itself and thus can accumulate in the periacrosmoal region by being trapped on these specialized membranes. Diffusion would then be sufficient to move these substances to this region. In support of this hypothesis are experiments in which I treated mature sperm with detergents, glycols, and hypotonic media, which solubilize or lift away the plasma membrane. The actin and its associated proteins remain attached to these specialized membranes. Thus actin can be nonrandomly distributed in cells in a nonfilamentous state presumably by its association with specialized membranes.

Ultrastructure and development of urediospore ornamentation in Melampsora lini

1971 ◽  
Vol 49 (12) ◽  
pp. 2067-2073 ◽  
Author(s):  
L. J. Littlefield ◽  
C. E. Bracker
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Outer Surface ◽  
Spore Wall ◽  
Wall Material ◽  
Wild Type ◽  
Melampsora Lini ◽  
Inner Surface ◽  
External Position ◽  
Basal Portion

The urediospores of Melampsora lini (Ehrenb.) Lev. are echinulate, with spines ca. 1 μ long over their surface. The spines are electron-transparent, conical projections, with their basal portion embedded in the electron-dense spore wall. The entire spore, including the spines, is covered by a wrinkled pellicle ca. 150–200 Å thick. The spore wall consists of three recognizable layers in addition to the pellicle. Spines form initially as small deposits at the inner surface of the spore wall adjacent to the plasma membrane. Endoplasmic reticulum occurs close to the plasma membrane in localized areas near the base of spines. During development, the spore wall thickens, and the spines increase in size. Centripetal growth of the wall encases the spines in the wall material. The spines progressively assume a more external position in the spore wall and finally reside at the outer surface of the wall. A mutant strain with finely verrucose spores was compared to the wild type. The warts on the surface of the mutant spores are rounded, electron-dense structures ca. 0.2–0.4 μ high, in contrast to spines of the wild type. Their initiation near the inner surface of the spore wall and their eventual placement on the outer surface of the spore are similar to that of spines. The wall is thinner in mutant spores than in wild-type spores.

scholarly journals A morphological study of plasma and phagosome membranes during endocytosis in Acanthamoeba.

1980 ◽  
Vol 84 (2) ◽  
pp. 246-260 ◽  
Author(s):  
B Bowers
Keyword(s):  
Plasma Membrane ◽  
Morphological Study ◽  
Direct Evidence ◽  
Particle Density ◽  
Early Stage ◽  
Chemical Analyses ◽  
Surface Separation ◽  
Phospholipid Ratio ◽  
Major Route ◽  
Particle Ingestion

Particle ingestion by Acanthamoeba is rapid. Within 40 s bound particles can be surrounded by pseudopods, brought into the cytoplasm, and released as phagosomes into the cytoplasmic stream. In electron micrographs the phagosome appears as a flasklike invagination of the surface. Separation from the surface occurs by fragmentation of the attenuated "neck+ of the invagination. The separated phagosome membrane has a three- to fourfold greater density of intramembrane particles than the plasma membrane from which it derives. This change is evident within 15 min of ingestion and is detectable while the membrane is still tightly apposed to the particle. There is no direct evidence for the mechanism of this increase; no increase in particle density was seen in the membrane at an early stage in the forming phagosomes still connected to the surface. These morphological observations are consistent with chemical analyses, to be reported in a separate communication, that show that the phagosome membrane has a higher protein to phospholipid ratio and a higher glycosphingolipid content than the plasma membrane. Enlarged phagosomes (presumptive phagolysosomes) show multiple small vesiculations of characteristic morphology. The small vesicles are postulated to be the major route of membrane return to the cell surface.

Investigation of the role of microtubules in protein secretion from lactating mouse mammary epithelial cells

1992 ◽  
Vol 102 (2) ◽  
pp. 239-247 ◽  
Author(s):  
M.E. Rennison ◽  
S.E. Handel ◽  
C.J. Wilde ◽  
R.D. Burgoyne
Keyword(s):  
Plasma Membrane ◽  
Epithelial Cells ◽  
Protein Secretion ◽  
Secretory Pathway ◽  
Mammary Epithelial Cells ◽  
Early Stage ◽  
Major Effect ◽  
Vesicle Transport ◽  
Mammary Epithelial ◽  
Mammary Cells

Disruption of microtubules has been shown to reduce protein secretion from lactating mammary epithelial cells. To investigate the involvement of microtubules in the secretory pathway in these cells we have examined the effect of nocodazole on protein secretion from mammary epithelial cells derived from the lactating mouse. Mouse mammary cells have extensive microtubule networks and 85% of their tubulin was in a polymeric form. Treatment with 1 micrograms/ml nocodazole converted most of the tubulin into a soluble form. In a continuous labelling protocol it was found that nocodazole did not interfere with protein synthesis but over a 5 h period secretion was markedly inhibited. To determine whether the inhibition was at the level of early or late stages of the secretory pathway mammary cells were pulse-labelled for 1 h to label protein throughout the secretory pathway before nocodazole treatment. When secretion was subsequently assayed it was found to be slower and only partially inhibited. These findings suggest that the major effect of nocodazole is on an early stage of the secretory pathway and that microtubules normally facilitate vesicle transport to the plasma membrane. An involvement of microtubules in vesicle transport to the plasma membrane is consistent with an observed accumulation of casein vesicles in nocodazole-treated cells. Exocytosis stimulated by the calcium ionophore ionomycin was unaffected by nocodazole treatment. We conclude from these results that the major effect of nocodazole is at an early stage of the secretory pathway, one possible target being casein vesicle biogenesis in the trans-Golgi network.

Evidence for microtubule nucleation at plasma membrane-associated sites in Drosophila

1987 ◽  
Vol 88 (1) ◽  
pp. 95-107 ◽  
Author(s):  
M.M. Mogensen ◽  
J.B. Tucker
Keyword(s):  
Plasma Membrane ◽  
Cell Differentiation ◽  
Cross Section ◽  
Plasma Membranes ◽  
Early Stage ◽  
Apical Cell ◽  
Apical Plasma Membrane ◽  
Cell Surfaces ◽  
Microtubule Organizing Centres ◽  
Oriented Parallel

This report is concerned with the nucleation and organization of microtubule bundles that assemble after ‘conventional’ centrosomal microtubule-organizing centres have been lost. The microtubule bundles in question span the lengths of wing epidermal cells. Bundles extend between hemidesmosomes at the apical cuticle-secreting surfaces of cells and basal attachment desmosomes that unite the dorsal and ventral epidermal layers of developing wing blades. Furthermore, each bundle includes up to 1500 microtubules and most of the microtubules are composed of 15 protofilaments. Individual cells were serially cross-sectioned at an early stage of bundle assembly. The number of microtubule profiles/cell cross-section decreased progressively by up to 59% of the most apical values in section sequences cut from fairly apical to more basal levels in the cells. The apical ends of microtubules were associated with numerous small dense plaque-like sites (diameter 0.1-0.2 micron), which were specialized regions of plasma membranes at the apical surfaces of cells. Many of the microtubules near apical plaques were not well aligned with each other; they ‘radiated away’ from cell apices. This was in contrast to the situation at more basal levels where most microtubules were oriented parallel to the longitudinal axes of cells. These findings indicate that the relatively dispersed arrays of apical plasma membrane-associated plaques act as microtubule-nucleating sites to initiate basally directed elongation of bundle microtubules. Apical cell surfaces and their plaques seem to operate as microtubule-nucleating and -organizing regions that functionally replace the centrosomal microtubule-organizing centres lost earlier in cell differentiation.

Numerical Investigation on Mixed Mode (I-II) Fracture Propagation of CCBD Specimens Under Confining Pressure

2021 ◽  
pp. 2050111
Author(s):  
Jiuzhou Huang ◽  
Jianxiong Li ◽  
Xin Pan ◽  
Tianzhou Xie ◽  
Wen Hua ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Numerical Method ◽  
Mixed Mode ◽  
Early Stage ◽  
Relative Length ◽  
Confining Pressure ◽  
Secondary Development ◽  
Weight Functions ◽  
Mode I ◽  
Initiation And Propagation

A new numerical method, verified by the analytical solution of the weight functions and experimental paths, is developed to evaluate the crack initiation and propagation generally in mixed mode (I-II). This numerical method combining the interaction integral method and the maximum tangential stress (MTS) criterion is based on the finite element method of secondary development. The influence of combined confining pressure and diametric forces on crack propagation trajectories for CCBD specimens are studied. It is indicated that the crack propagation direction independent of the confining pressure keeps the same with the line of original crack as the loading angle is equal to [Formula: see text]. But when the loading angle is greater than [Formula: see text], the curvature of the curve trajectory in the early stage of crack propagation increases with a larger confining pressure. Further, it is found that larger values of the loading angle and relative length will make the effect of confining pressure more significant at the early stage of crack growth.

Sign in / Sign up

Export Citation Format

Share Document