Experimental studies on the shoot apex of Helianthus annuus: the effect of surgical bisection on quiescent cells in the apex

1977 ◽  
Vol 55 (5) ◽  
pp. 606-614 ◽  
Author(s):  
E. L. Davis ◽  
T. A. Steeves
Keyword(s):  
Dna Synthesis ◽  
Helianthus Annuus ◽  
Shoot Apex ◽  
Experimental Studies ◽  
Central Zone ◽  
Quiescent Cells ◽  
Cytological Features

When the shoot apex of Helianthus annuus cv. Peredovic is bisected surgically, two new apices are regenerated, each of which, 3 weeks after the operation, contains a quiescent central zone similar to that of the original apex. The operation destroys some cells of the original zone and stimulates others to become active in DNA synthesis. Regenerating apices, supplied with [H3] thymidine and autoradiographed at the end of the 2nd day after the operation, reveal no evidence of a quiescent zone. Evidence for the establishment of quiescence appears by the end of the 3rd day and becomes clearer on the 4th and 5th days after the operation. There is no evidence that the residual zone cells play any particular role in regeneration. It is suggested that quiescence in regard to DNA synthesis and mitosis appears sooner than the cytological features associated with quiescence in the sunflower shoot apex.

Further analytical and experimental studies on the shoot apex of Helianthus annuus: variable activity in the central zone

1979 ◽  
Vol 57 (8) ◽  
pp. 971-980 ◽  
Author(s):  
E. L. Davis ◽  
Patricia Rennie ◽  
Taylor A. Steeves
Keyword(s):  
Helianthus Annuus ◽  
Mitotic Activity ◽  
Shoot Apex ◽  
Experimental Studies ◽  
Central Zone ◽  
Peripheral Zone ◽  
Intact Plants ◽  
Cast Doubt ◽  
Young Leaves ◽  
Mitotic Frequency

The cytologically distinctive central zone of the vegetative shoot apex of Helianthus annuus L. cv. Peredovic has a mitotic frequency considerably lower than that of the surrounding peripheral zone in intact plants. Apices excised and grown in culture for 5 days before being supplied with [H3]thymidine reveal a correspondingly low level of DNA synthesis in the central zone when autoradiographed. In similarly cultured apices, mitotic activity in the central zone is less than that recorded for intact plants. Labelling immediately after excision of the apex indicates that the central zone cells are activated by the operation and quiescence returns during the following 5 days. This activation is confirmed by mitotic counts 2 days after excision. The removal of only two young leaves from the apical buds of otherwise intact plants results in a comparable stimulation of mitotic activity in the central zone. These observations cast doubt upon the significance of mitotic activity in living shoot apices when these have been exposed for observation by removal of leaves. They also raise questions about the validity of labelling techniques which involve the partial dissection of the shoot apex.

Quiescent cell populations in apical meristems of Helianthus annuus

1974 ◽  
Vol 52 (10) ◽  
pp. 2195-2201 ◽  
Author(s):  
Haviva D. Langenauer ◽  
Edward L. Davis ◽  
Peter L. Webster
Keyword(s):  
Dna Synthesis ◽  
Helianthus Annuus ◽  
Shoot Apex ◽  
Central Zone ◽  
Quiescent Cell ◽  
Shoot Meristem ◽  
Cell Populations ◽  
Quiescent Center ◽  
Apical Meristems ◽  
Shoot Apical Meristems

Quiescent cell populations in both root and shoot apical meristems of Helianthus annuus are compared. Histoautoradiographs prepared after 12-h provision of [3H]thymidine in the growth medium demonstrate the presence of a quiescent center located subterminally in the apical meristem of cultured and attached Helianthus roots. Similar techniques (using [3H]-thymidine in the medium for 24–48 h) show that while cells of the shoot meristem undergo DNA synthesis, a central zone that does not incorporate the precursor exists at the summit of the cultured vegetative shoot apex. Central zone cells contain larger nuclei than do surrounding cells in the shoot apex, while quiescent-center nuclei are smaller than those in the surrounding meristem of the root apex.Growth of excised roots in medium without carbohydrates causes temporary arrest of proliferative activity in most of the meristem. When sucrose is provided after this treatment, cells of the meristem as well as most cells of the root quiescent center are stimulated into DNA synthesis. In shoots cultured in sucrose-deficient medium, few cells continue to synthesize DNA, but subsequent transfer to medium with carbohydrates stimulates no cells of the central zone into DNA synthesis, although progression through the cycle is resumed by other cells of the meristem. These and other considerations suggest that the quiescent regions in root and shoot apical meristems are not comparable.

Analytical studies on the shoot apex of Helianthus annuus

1969 ◽  
Vol 47 (9) ◽  
pp. 1367-1375 ◽  
Author(s):  
T. A. Steeves ◽  
M. Anne Hicks ◽  
J. M. Naylor ◽  
Patricia Rennie
Keyword(s):  
Helianthus Annuus ◽  
Shoot Apex ◽  
Culture Medium ◽  
Deoxyribonucleic Acid ◽  
Vegetative State ◽  
Central Zone ◽  
Apical Region ◽  
Cell Nuclei ◽  
Liquid Culture Medium ◽  
Vegetative Shoot Apex

The vegetative shoot apex of Helianthus annuus contains a central zone in which the cell nuclei are relatively large and stain faintly in the Feulgen reaction. Excised apices in the vegetative state were supplied with thymidine-H3 through their sterile, liquid culture medium. Autoradiography after 24 or 48 hours of feeding revealed no significant incorporation of the labeled precursor into central zone nuclei, but extensive incorporation in peripheral regions of the apex. It is concluded that during vegetative growth deoxyribonucleic acid (DNA) synthesis and mitosis are arrested in the central zone or reduced to an extremely slow rate. Microspectrophotometry, however, indicates that the central zone nuclei are not held at the 2C level. With the onset of flowering, cytological zonation disappears in the apex and the incorporation of thymidine-H3 is uniformly heavy throughout the apical region.

The ultrastructure of the central zone cells of the shoot apex of Helianthus annuus

1981 ◽  
Vol 59 (11) ◽  
pp. 2009-2015 ◽  
Author(s):  
V. K. Sawhney ◽  
P. J. Rennie ◽  
T. A. Steeves
Keyword(s):  
Endoplasmic Reticulum ◽  
Helianthus Annuus ◽  
Shoot Apex ◽  
Ultrastructural Study ◽  
Central Zone ◽  
Peripheral Zone ◽  
Striking Difference ◽  
Vegetative Shoot ◽  
Helianthus Annuus L ◽  
Vegetative Shoot Apex

An ultrastructural study of the vegetative shoot apex of Helianthus annuus L. cv. Peredovic has shown that in most respects the cytoplasmic components of the central zone cells were similar to those of the mitotically active peripheral zone cells. For example, the mitochondria, dictyosomes, endoplasmic reticulum, ribosomes, and microtubules were not different either in their structure or in distribution in the two types of cells. The only striking difference found was the presence of starch-containing plastids in the central zone, primarily in the two tunica layers in this region, and their absence from peripheral and immediately subjacent regions of the meristem. Starch-containing plastids were observed in the differentiating pith cells. Plasmodesmata were observed in the central zone and in walls between central and peripheral zone cells.

Ontogenetical and experimental studies of the floral apex of Portulaca grandiflora. 1. Histology of transformation of the shoot apex into the floral apex

1969 ◽  
Vol 47 (1) ◽  
pp. 133-140 ◽  
Author(s):  
Siti Raswati Soetiarto ◽  
Ernest Ball
Keyword(s):  
Shoot Apex ◽  
Experimental Studies ◽  
Floral Meristem ◽  
Vegetative Shoot ◽  
Floral Organs ◽  
Mature Flower ◽  
Floral Apex ◽  
Portulaca Grandiflora ◽  
Floral Primordia ◽  
Vegetative Shoot Apex

The vegetative apex was a low dome consisting of two layers of tunica surmounting a very small corpus. Foliar primordia originated as periclines in the flanks of T2. The transition apex became first a steep cone and then a hemisphere. All floral primordia—the two bracts, the two sepals, the several whorls of petals, the several whorls of stamens, and the carpels—originated in the manner of leaves, as periclines in T2 on the flanks of the apex. All appendages, including carpels, were therefore lateral. In the early transition, the apex had a brief stage in which there were three tunica layers, but the inner one was lost with the onset of the sepals. The bracts and the first sepal continued the normal positions of primordia for the vegetative phyllotaxy of 3/8, but with the second sepal, this phyllotaxy was lost, and petals, stamens, and carpels were produced in whorls. While leaves, bracts, sepals, and petals were produced in acropetal sequence, stamens were produced in basipetal sequence, and carpels appeared simultaneously. After carpels were formed, the rest of the floral apex underwent a brief period of expansion growth, achieving a diameter comparable to that of a shoot apex, but its substance was eventually incorporated into the carpel margins, which later produced the ovules. This agrees with the determinate nature of the floral apex. During the development of the first series of floral organs, the floral apex underwent continued increase in area, finally achieving a diameter several times that of the vegetative shoot apex. Its size and form were such that they were compared to those of some inflorescence apices. After development of the first series of floral organs, the subjacent tissues to the floral meristem underwent divisions and elongation at right angles to the axis, causing at first a flattening of the meristem, and eventually a cup-shaped form, with the carpels attached in the bottom of a bowl. The mature flower was thus perigynous, but this development arose quite differently from the perigyny as it is known from ontogenetic studies in the Rosaceae.

scholarly journals Technological Features in Processing of Conical Lenses

2020 ◽  
Vol 19 (6) ◽  
pp. 521-527
Author(s):  
M. I. Filonova ◽  
R. O. Dias Gonzalez ◽  
A. A. Sukhotzkiy ◽  
A. S. Kozeruk ◽  
A. V. Semchuonok
Keyword(s):  
Glass Plate ◽  
Experimental Studies ◽  
Central Zone ◽  
Conical Surface ◽  
Work Piece ◽  
Cylindrical Shape ◽  
Cylindrical Blank ◽  
Machined Surface ◽  
Optimal Sequence ◽  
Plane Parallel

The paper presents the technology of obtaining flat-conical lenses (axicons) by the method of free grinding a work-piece to a flat tool through a layer of abrasive suspension. For this, theoretical and experimental studies of the regularities of stock removal from the base of the cone and its lateral surface have been carried out. The processing modes have been identified that ensure both uniform operation of the flat surface of  the part and enhanced removal of  the allowance in the edge or central zone of this surface. During the study of the processing of the conical surface, the set-up parameters of the technological equipment have been established, at which there is a minimum deviation of the generatrix of the cone from straightness and maximum productivity of the process. The stages of processing conical lenses are proposed, which allow to assign the optimal sequence of operations in the manufacture of this type of parts from blanks of a cylindrical shape in cases where  the ratio of the height of the cone to the diameter of its base H/d £ 0.5. The main stages of processing include: grinding of the bases of cylindrical blanks with maintaining their mutual parallelism with a given accuracy; polishing one of the cylinder bases to achieve the required roughness and deviation from non-flatness; fastening a cylindrical blank to an auxiliary plane-parallel glass plate using molecular cohesion forces; mechanical fastening of a cylindrical work-piece with a collet adapter mandrel for a plane-parallel glass plate; applying the nearest sphere to the second base of the cylindrical blank; drawing a conical surface on the spherical part of a plano-convex lens; grinding and polishing the conical surface to achieve the required roughness  and straightness of the cone generatrix. The degree of efficiency of the setup parameters of the machine has been revealed depending on the technological heredity of the work-piece from the point of view of the distribution of the allowance to be removed over the machined surface. 

scholarly journals Specific activation of p85-p110 phosphatidylinositol 3'-kinase stimulates DNA synthesis by ras- and p70 S6 kinase-dependent pathways.

1997 ◽  
Vol 17 (1) ◽  
pp. 248-255 ◽  
Author(s):  
J McIlroy ◽  
D Chen ◽  
C Wjasow ◽  
T Michaeli ◽  
J M Backer
Keyword(s):  
Dna Synthesis ◽  
Affinity Purification ◽  
Specific Inhibitor ◽  
Brdu Incorporation ◽  
Glutathione S Transferase ◽  
Intact Cells ◽  
S6 Kinase ◽  
P70 S6 Kinase ◽  
Quiescent Cells

We have developed a polyclonal antibody that activates the heterodimeric p85-p110 phosphatidylinositol (PI) 3'-kinase in vitro and in microinjected cells. Affinity purification revealed that the activating antibody recognized the N-terminal SH2 (NSH2) domain of p85, and the antibody increased the catalytic activity of recombinant p85-p110 dimers threefold in vitro. To study the role of endogenous PI 3'-kinase in intact cells, the activating anti-NSH2 antibody was microinjected into GRC + LR73 cells, a CHO cell derivative selected for tight quiescence during serum withdrawal. Microinjection of anti-NSH2 antibodies increased bromodeoxyuridine (BrdU) incorporation fivefold in quiescent cells and enhanced the response to serum. These data reflect a specific activation of PI 3'-kinase, as the effect was blocked by coinjection of the appropriate antigen (glutathione S-transferase-NSH2 domains from p85 alpha), coinjection of inhibitory anti-p110 antibodies, or treatment of cells with wortmannin. We used the activating antibodies to study signals downstream from PI 3'-kinase. Although treatment of cells with 50 nM rapamycin only partially decreased anti-NSH2-stimulated BrdU incorporation, coinjection with an anti-p70 S6 kinase antibody effectively blocked anti-NSH2-stimulated DNA synthesis. We also found that coinjection of inhibitory anti-ras antibodies blocked both serum- and anti-NSH2-stimulated BrdU incorporation by approximately 60%, and treatment of cells with a specific inhibitor of MEK abolished antibody-stimulated BrdU incorporation. We conclude that selective activation of physiological levels of PI 3'-kinase is sufficient to stimulate DNA synthesis in quiescent cells. PI 3'-kinase-mediated DNA synthesis requires both p70 S6 kinase and the P21ras/MEK pathway.

Apoptosis in megaloblastic anemia occurs during DNA synthesis by a p53-independent, nucleoside-reversible mechanism

Blood ◽  
2000 ◽  
Vol 96 (9) ◽  
pp. 3249-3255 ◽  
Author(s):  
Mark J. Koury ◽  
James O. Price ◽  
Geoffrey G. Hicks
Keyword(s):  
Dna Synthesis ◽  
De Novo ◽  
Megaloblastic Anemia ◽  
Experimental Studies ◽  
Hematopoietic Cells ◽  
S Phase ◽  
De Novo Synthesis ◽  
Complete Reversal ◽  
Phase Accumulation

Abstract Deficiency of folate or vitamin B12 (cobalamin) causes megaloblastic anemia, a disease characterized by pancytopenia due to the excessive apoptosis of hematopoietic progenitor cells. Clinical and experimental studies of megaloblastic anemia have demonstrated an impairment of DNA synthesis and repair in hematopoietic cells that is manifested by an increased percentage of cells in the DNA synthesis phase (S phase) of the cell cycle, compared with normal hematopoietic cells. Both folate and cobalamin are required for normal de novo synthesis of thymidylate and purines. However, previous studies of impaired DNA synthesis and repair in megaloblastic anemia have concerned mainly the decreased intracellular levels of thymidylate and its effects on nucleotide pools and misincorporation of uracil into DNA. An in vitro model of folate-deficient erythropoiesis was used to study the relationship between the S-phase accumulation and apoptosis in megaloblastic anemia. The results indicate that folate-deficient erythroblasts accumulate in and undergo apoptosis in the S phase when compared with control erythroblasts. Both the S-phase accumulation and the apoptosis were induced by folate deficiency in erythroblasts fromp53 null mice. The complete reversal of the S-phase accumulation and apoptosis in folate-deficient erythroblasts required the exogenous provision of specific purines or purine nucleosides as well as thymidine. These results indicate that decreased de novo synthesis of purines plays as important a role as decreased de novo synthesis of thymidylate in the pathogenesis of megaloblastic anemia.

scholarly journals A transient rise in cytosolic calcium follows stimulation of quiescent cells with growth factors and is inhibitable with phorbol myristate acetate.

1985 ◽  
Vol 101 (2) ◽  
pp. 372-379 ◽  
Author(s):  
P L McNeil ◽  
M P McKenna ◽  
D L Taylor
Keyword(s):  
Growth Factor ◽  
Dna Synthesis ◽  
Primary Source ◽  
Cytosolic Calcium ◽  
Ion Concentration ◽  
Free Calcium ◽  
Quiescent Cells ◽  
3T3 Fibroblasts ◽  
Transient Rise ◽  
20 Nm

We have used aequorin as an indicator for the intracellular free calcium ion concentration [( Ca++]i) of Swiss 3T3 fibroblasts. Estimated [Ca++]i of serum-deprived, subconfluent fibroblasts was 89 (+/-20) nM, almost twofold higher than that of subconfluent cells growing in serum, whose [Ca++]i was 50 (+/-19) nM. Serum, partially purified platelet-derived growth factor (PDGF), and fibroblast growth factor (FGF) stimulated DNA synthesis by the serum-deprived cells, whereas epidermal growth factor (EGF) did not. Serum immediately and transiently elevated the [Ca++]i of serum-deprived cells, which reached a maximal value of 5.3 microM at 18 s poststimulation but returned to near prestimulatory levels within 3 min. Moreover, no further changes in [Ca++]i were observed during 12 subsequent h of continuous recording. PDGF produced a peak rise in [Ca++]i to approximately 1.4 microM at 115 s after stimulation, and FGF to approximately 1.2 microM at 135 s after stimulation. EGF caused no change in [Ca++]i. The primary source of calcium for these transients was intracellular, since the magnitude of the serum-induced rise in [Ca++]i was reduced by only 30% in the absence of exogenous calcium. Phorbol 12-myristate 13-acetate (PMA) had no effect on resting [Ca++]i. When, however, quiescent cells were treated for 30 min with 100 nM PMA, serum-induced rises in [Ca++]i were reduced by sevenfold. PMA did not inhibit growth factor-induced DNA synthesis and was by itself partially mitogenic. We suggest that if calcium is involved as a cytoplasmic signal for mitogenic activation of quiescent fibroblasts, its action is early, transient, and can be partially substituted for by PMA. Activated protein kinase C may regulate growth factor-induced increases in [Ca++]i.

scholarly journals Apparent respiratory discrimination is correlated with growth rate in the shoot apex of sunflower (Helianthus annuus)

2004 ◽  
Vol 55 (408) ◽  
pp. 2599-2605 ◽  
Author(s):  
T. W. Ocheltree
Keyword(s):  
Growth Rate ◽  
Helianthus Annuus ◽  
Shoot Apex
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