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.

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.

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.

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.

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.

The distribution of ribosomes in the vegetative and floral apices of Adonis aestivalis

1976 ◽  
Vol 54 (21) ◽  
pp. 2478-2483 ◽  
Author(s):  
Joseph Lin ◽  
Ernest M. Gifford Jr.
Keyword(s):  
Shoot Apex ◽  
Unit Volume ◽  
Central Zone ◽  
Peripheral Zone ◽  
Cell Basis ◽  
Transition To Flowering

The distribution of ribosomes and changes in the ratio of polyribosomes to monoribosomes were determined for the vegetative, transitional, and floral apices of Adonis aestivalis L., a day-neutral plant. Ribosomal counts were made with a Quantimet 720 image-analyzing computer. Two methods in the analysis of the shoot apex were compared: (1) ribosomal distribution based upon the average number of ribosomes per unit volume of cytoplasm (concentration) and (2) distribution based upon total number of ribosomes per cell.It was found that the concentration of ribosomes was greater in the peripheral zone than in the central zone. Increase occurred in the latter zone during transition to flowering. On a per cell basis, however, the number of ribosomes was the greatest in the rib meristem, followed by the central and peripheral zones. During transition to flowering, the number of ribosomes per cell increased only in the peripheral zone.It is suggested that consideration of ribosomal data on a per cell basis may be helpful in achieving a better understanding of the interzonal relationships within the shoot apex.

scholarly journals Translocation of 32P from leaves to seeds of sunflower and associated biochemical changes in young and mature leaves during seed-filling

2014 ◽  
Vol 53 (4) ◽  
pp. 489-498
Author(s):  
Suchanda Halder ◽  
Kajal Gupta
Keyword(s):  
Central Zone ◽  
Peripheral Zone ◽  
Stage I ◽  
Stage Ii ◽  
Stage Iii ◽  
High Accumulation ◽  
Retention Capacity ◽  
Mature Leaves ◽  
Central Disc ◽  
Young Leaves

Transport of <sup>32</sup>P from mature leaves was studied at stage I (ray florets opening), stage II (50% florets opening) and stage III (central disc florets opening) of the capitulum in order to ascertain the capacity of developing seeds to draw metabolites. Experiments showed that when feeding was done at stage I separately in the 6th, 7th and 8th leaf from the apex, accumulation of <sup>32</sup>P was maximum in the peripheral seeds of the corresponding zone of the fed leaf. Also at stage II was <sup>32</sup>P accumulation high in the peripheral zone along with high accumulation in the inner zone. But at stage III and IV (seven days after central disc florets opening) when accumulation declined considerably in the peripheral zone, very little accumulation of <sup>32</sup>P was noted in the central zone of the capitulum. During maximum sink demand i.e. at stage II, the soluble cabohydrate level increased both in apically borne young and mature leaves but declined thereafter only ,in mature leaves. In both young and mature leaves the chlorophyll level, however, did not show any decline even at stage IV, It was further observed that dry matter retention capacity declined only in young leaves from stage II onwards. In young leaves, catalase activity was low from stage II whereas in mature leaves it was low at stage II followed by a transient sharp increase at stage III.

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.

Three-Dimensional Analysis of Vestibular Efferent Neurons Innervating Semicircular Canals of the Gerbil

1997 ◽  
Vol 78 (6) ◽  
pp. 3234-3248 ◽  
Author(s):  
I. M. Purcell ◽  
A. A. Perachio
Keyword(s):  
Basement Membrane ◽  
Dimensional Analysis ◽  
Three Dimensional ◽  
Central Zone ◽  
Semicircular Canals ◽  
Peripheral Zone ◽  
Longitudinal Axis ◽  
Open Loop ◽  
Response Dynamics ◽  
Efferent Neurons

Purcell, I. M. and A. A. Perachio. Three-dimensional analysis of vestibular efferent neurons innervating semicircular canals of the gerbil. J. Neurophysiol. 78: 3234–3248, 1997. Anterograde labeling techniques were used to examine peripheral innervation patterns of vestibular efferent neurons in the crista ampullares of the gerbil. Vestibular efferent neurons were labeled by extracellular injections of biocytin or biotinylated dextran amine into the contralateral or ipsilateral dorsal subgroup of efferent cell bodies (group e) located dorsolateral to the facial nerve genu. Anterogradely labeled efferent terminal field varicosities consist mainly of boutons en passant with fewer of the terminal type. The bouton swellings are located predominately in apposition to the basolateral borders of the afferent calyces and type II hair cells, but several boutons were identified close to the hair cell apical border on both types. Three-dimensional reconstruction and morphological analysis of the terminal fields from these cells located in the sensory neuroepithelium of the anterior, horizontal, and posterior cristae were performed. We show that efferent neurons densely innervate each end organ in widespread terminal fields. Subepithelial bifurcations of parent axons were minimal, with extensive collateralization occurring after the axons penetrated the basement membrane of the neuroepithelium. Axonal branching ranged between the 6th and 27th orders and terminal field collecting area far exceeds that of the peripheral terminals of primary afferent neurons. The terminal fields of the efferent neurons display three morphologically heterogeneous types: central, peripheral, and planum. All cell types possess terminal fields displaying a high degree of anisotropy with orientations typically parallel to or within ±45° of the longitudinal axis if the crista. Terminal fields of the central and planum zones predominately project medially toward the transverse axis from the more laterally located penetration of the basement membrane by the parent axon. Peripheral zone terminal fields extend predominately toward the planum semilunatum. The innervation areas of efferent terminal fields display a trend from smallest to largest for the central, peripheral, and planum types, respectively. Neurons that innervate the central zone of the crista do not extend into the peripheral or planum regions. Conversely, those neurons with terminal fields in the peripheral or planum regions do not innervate the central zone of the sensory neuroepithelium. The central zone of the crista is innervated preferentially by efferent neurons with cell bodies located in the ipsilateral group e. The peripheral and planum zones of the crista are innervated preferentially by efferent neurons with cell bodies located in the contralateral group e. A model incorporating our anatomic observations is presented describing an ipsilateral closed-loop feedback between ipsilateral efferent neurons and the periphery and an open-loop feed-forward innervation from contralateral efferent neurons. A possible role for the vestibular efferent neurons in the modulation of semicircular canal afferent response dynamics is proposed.

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. 

Septoria helianthi. [Descriptions of Fungi and Bacteria].

1970 ◽  
Author(s):  
P. Holliday
Keyword(s):  
Helianthus Annuus ◽  
Geographical Distribution ◽  
Leaf Spot ◽  
Seed Treatment ◽  
Seed Transmission ◽  
Adaxial Surface ◽  
Young Leaves

Abstract A description is provided for Septoria helianthi. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Helianthus annuus, Helianthus grosseserratus and Helianthus rigidus. DISEASE: Leaf spot of sunflower. Yellowish spots up to 1.5 cm develop over the whole lamina, gradually turning necrotic and becoming almost black. The numerous pycnidia are mostly on the adaxial surface. The lesions have a polygonal outline, being sharply delimited by the veins. Infection may begin on the cotyledons and young leaves, spreading to later developing leaves. Severe attacks lead to defoliation and loss in yield. GEOGRAPHICAL DISTRIBUTION: Fairly widespread in E. Europe and the U.S.S.R. in Asia, China, Japan, Australia (Qd.); E. and S. Africa, N. America (CMI Map 468, ed. 1, 1970). TRANSMISSION: Overwintering occurs in host debris. Seed treatment is recommended although seed transmission does not appear to have been demonstrated. Introduction of the fungus into Hungary may have been via seed (43, 2013).

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