Influence de la photopériode sur le comportement du méristème caulinaire du Celosia cristata

1977 ◽  
Vol 55 (11) ◽  
pp. 1488-1500
Author(s):  
D. Driss-Ecole
Keyword(s):  
Mitotic Activity ◽  
Shoot Apex ◽  
Unstable State ◽  
Axial Zone ◽  
Histological Studies ◽  
Daily Show ◽  
Differentiated Cells ◽  
Long Day ◽  
Celosia Cristata ◽  
High Level

Three groups of plants of Celosia cristata were grown in a 8-h, 12-h, or 16-h day. Histological studies of the shoot apex were performed during the vegetative and the prefloral phases.The apical meristems of the plants subjected to long-day conditions (16 h) flatten (fasciation). At the beginning of the fasciation, an activation of the corpus and a restructuration of the meristem are observed. The transformed meristem shows four superficial layers which cover a group of differentiated cells. The zonation is always recognizable and the apex initiates numerous leaves. The broadening of the meristem is due to the high level of mitotic activity of two opposite regions in the ‘anneau initial’ which takes an elliptical shape and to the peculiar orientation of the mitoses. During this transformation the volumes of the lateral and medullary zones increase while the volume of the axial zone remains almost identical. The long vegetative phase ceases with the homogeneization of the meristematic state of the four superficial layers and with the edification of a prefloral crest.The apex of plants grown under an 8-h photoperiod remains small sized. They never undergo fasciation and reach the prefloral phase very quickly.The meristems of the plants cultivated under 12 h of light daily show an unstable state and sometimes evolve tardily towards fasciation.

Visualisation des centres générateurs selon la théorie phyllotaxique de Plantefol, dans le point végétatif du grand frêne (Fraxinus excelsior)

1984 ◽  
Vol 62 (12) ◽  
pp. 2636-2643 ◽  
Author(s):  
Alain Cottignies
Keyword(s):  
Cell Proliferation ◽  
Mitotic Activity ◽  
Poisson Distribution ◽  
Shoot Apex ◽  
Unit Area ◽  
Fraxinus Excelsior ◽  
Nearest Neighbour ◽  
Axial Zone ◽  
Cell Cycles ◽  
Mitotic Wave

To visualize the generative center of each foliar helix and its oriented progression, cell proliferation was studied in the ash (Fraxinus excelsior L.) shoot apex. The distribution of mitosis was analysed first with the hypothesis of the multiple foliar helices phyllotactic theory and then without any preliminary hypothesis. The cell cycles were asynchronic and mitotic duration was constant. Therefore, the parameters of both the Poisson distribution of mitosis in each apical zone and of mitotic density, evaluated by the nearest-neighbour method or by the rotation of a unit area, were indicative of the cell proliferation level. The axial zone differed from the initiating ring by virtue of its lower mitotic activity. The initiating ring was heterogeneous and involved two parts which were opposite each other and symmetrical with regard to the axis of the apex. In each half, the cell proliferation increased gradually to a generative center with a maximal mitotic activity, then decreased twice as fast. This heterogeneity showed the necessary rotation of a privileged mitotic wave, which progressed step by step in a single direction. The cartography of the cell proliferation intensity was mapped for one sample meristcm.

scholarly journals The E1^E4 Protein of Human Papillomavirus Interacts with the Serine-Arginine-Specific Protein Kinase SRPK1

2007 ◽  
Vol 81 (11) ◽  
pp. 5437-5448 ◽  
Author(s):  
Ian Bell ◽  
Ashley Martin ◽  
Sally Roberts
Keyword(s):  
Human Papillomavirus ◽  
Protein Kinase ◽  
Specific Protein ◽  
Replication Cycle ◽  
Differentiated Cells ◽  
Rich Domain ◽  
Productive Phase ◽  
High Level ◽  
Specific Protein Kinase

ABSTRACT Human papillomavirus (HPV) infections of the squamous epithelium are associated with high-level expression of the E1^E4 protein during the productive phase of infection. However, the precise mechanisms of how E1^E4 contributes to the replication cycle of the virus are poorly understood. Here, we show that the serine-arginine (SR)-specific protein kinase SRPK1 is a novel binding partner of HPV type 1 (HPV1) E1^E4. We map critical residues within an arginine-rich domain of HPV1 E1^E4, and in a region known to facilitate E1^E4 oligomerization, that are requisite for SRPK1 binding. In vitro kinase assays show that SRPK1 binding is associated with phosphorylation of an HPV1 E1^E4 polypeptide and modulates autophosphorylation of the kinase. We show that SRPK1 is sequestered into E4 inclusion bodies in terminally differentiated cells within HPV1 warts and that colocalization between E1^E4 and SRPK1 is not dependent on additional HPV1 factors. Moreover, we also identify SRPK1 binding of E1^E4 proteins of HPV16 and HPV18. Our findings indicate that SRPK1 binding is a conserved function of E1^E4 proteins of diverse virus types. SRPK1 influences important biochemical processes within the cell, including nuclear organization and RNA metabolism. While phosphorylation of HPV1 E4 by SRPK1 may directly influence HPV1 E4 function during the infectious cycle, the modulation and sequestration of SRPK1 by E1^E4 may affect the ability of SRPK1 to phosphorylate its cellular targets, thereby facilitating the productive phase of the HPV replication cycle.

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 Acceleration of Primordium Initiation as a Component of Floral Evocation in Lolium temulentum L

1996 ◽  
Vol 23 (5) ◽  
pp. 569 ◽  
Author(s):  
LT Evans ◽  
C Blundell
Keyword(s):  
Shoot Apex ◽  
Floral Development ◽  
Growth Retardant ◽  
Leaf Primordium ◽  
Essential Component ◽  
Lolium Temulentum ◽  
Long Day ◽  
External Sign ◽  
Floral Evocation

An acceleration of leaf primordium initiation by the shoot apex frequently follows floral evocation, but after varying intervals. The purpose of the experiments reported here was to define more closely the relation between this reduction of the plastochron and floral evocation, using the long day (LD) plant Lolium temulentum grown under closely controlled conditions.The acceleration begins at floral evocation, on the day after the first LD exposure, and increases after exposure to additional LDs. However, plants too young to be florally evoked by one LD nevertheless manifested an acceleration of primordium initiation, so the acceleration alone is not sufficient for evocation. Single applications of highly florigenic gibberellins (GAs), such as GA5, also accelerate the initiation of primordia and floral development, more so than does the weakly florigenic GA1. By contrast, single applications of the growth retardant Trinexapac-ethyl (CGA 163'935) to plants given one LD largely prevented the acceleration of primordium initiation but without inhibiting floral development. Thus, although the acceleration of primordium initiation by LD or by GA application is the first external sign of floral evocation in L. temulentum, it is neither a sufficient nor an essential component of it.

MITOTIC ACTIVITY AT THE SHOOT APEX OF AZOLLA FILICULOIDES

1981 ◽  
Vol 68 (8) ◽  
pp. 1050-1055 ◽  
Author(s):  
Ernest M. Gifford ◽  
Vito S. Polito
Keyword(s):  
Mitotic Activity ◽  
Shoot Apex ◽  
Azolla Filiculoides

scholarly journals The effects of experimentally induced rest and exercise on the epidermal mitotic activity of the adult male mouse, Mus musculus L

1948 ◽  
Vol 135 (879) ◽  
pp. 233-242 ◽  
Keyword(s):  
Mitotic Activity ◽  
Adult Male ◽  
Male Mouse ◽  
Time Of Day ◽  
Excessive Exercise ◽  
Adult Male Mouse ◽  
Preliminary Study ◽  
High Level ◽  
Mitosis Rate ◽  
Rest And Exercise

As a preliminary study of the conditions which affect the hour to hour variations in epidermal mitotic activity in the adult male mouse, experiments were carried out involving artificially induced sleep and exercise. In the first experiment the animals were injected with a dose of barbiturates sufficient to induce sleep for a period of 3 or 4 hr. at a time of day when they were usually active. The injections were given at 17.00 hr. as the animals were waking from their afternoon sleep, and they resulted in a sharp rise in mitotic activity. A maximum was reached at 20.00 hr., the time when the mitotic activity of the controls had dropped to a minimum. As the animals recovered and became active, their mitosis rate fell quickly to a low level. In the second experiment the animals were placed in a slowly revolving box, and so forced to remain awake and active throughout an afternoon when they would otherwise have been asleep. This treatment resulted in extremely low mitotic activity, in contrast to which that of the normally sleeping controls rose to a high level. It is probably significant that when the mice were released from the revolving box, and could at last sleep, their mitosis rate remained low. This suggests that the excessive exercise had either resulted in the production of some mitosis-depressing substance which remained in the system, or that some substance vital to mitosis had been used up and took some time to be replaced. The conclusion is now justified that the rate of epidermal mitosis normally increases during sleep, and decreases during hours of wakefulness and exercise. In this way the form of the diurnal mitosis cycle is determined by the habits of the animals.

scholarly journals Inflorescence Initiation in Lolium Temulentum L. X. Changes in 32p Incorporation into Nucleic Acids of the Shoot Apex at Induction

1967 ◽  
Vol 20 (1) ◽  
pp. 13 ◽  
Author(s):  
AHGC Rijven ◽  
LT Evans
Keyword(s):  
Nucleic Acids ◽  
Shoot Apex ◽  
Floral Induction ◽  
Transient Increase ◽  
Lolium Temulentum ◽  
Long Day ◽  
32P Incorporation ◽  
Summit Region

Previous studies have shown an increase in RNA at the shoot apex of L. temulentum following floral induction, detectable chemically 2 days after induction, and by histochemical means after 1 day. Here, a transient increase in the incorporation of 32P, applied to leaves, into nucleic acids at the apex is shown to occur at about the time when the long-day stimulus is estimated to reach the shoot apex. The increased 32p incorporation due to the long-day exposure occurs throughout the apex, and is not confined to the summit region. Most of the 32p was incorporated into RNA.

Early increased expression of a cyclin-dependant protein kinase (LtCDKA1;1) during inflorescence initiation of the long day grass Lolium temulentum

2013 ◽  
Vol 40 (10) ◽  
pp. 986 ◽  
Author(s):  
Greg F. W. Gocal ◽  
Rod W. King
Keyword(s):  
Cell Division ◽  
Shoot Apex ◽  
Target Cells ◽  
Serine Threonine Kinase ◽  
Lolium Temulentum ◽  
Apical Dome ◽  
Long Day ◽  
Vegetative Shoot Apex ◽  
Weak Expression

Knowing where and when different genes express at the shoot apex during the transition to flowering will help in understanding this developmental switch. The CDKA family of serine/threonine kinase genes are appropriate candidates for such developmental switching as they are involved in the regulation of the G1/S and G2/M boundaries of the cell cycle (see review by Dudits et al. 2007) and so could regulate increases of cell division associated with flowering. Furthermore, in rice stems the gibberellin (GA) class of plant growth regulators rapidly upregulate CDKA expression and cell division. Thus, CDKA expression might be linked to the florigenic action of GA as a photoperiodically-generated, signal. For the grass Lolium temulentum L., we have isolated an LtCDKA1;1 gene, which is upregulated in shoot apices collected soon after the start of a single florally inductive long day (LD). In contrast to weak expression of LtCDKA1;1 in the vegetative shoot apex, in situ and PCR-based mRNA assays and immunological studies of its protein show very rapid increases in the apical dome at the time that florigenic signals arrive at the apex (<6 h after the end of the LD). By ~54 h LtCDKA1;1 mRNA is localised to the floral target cells, the spikelet primordia. Later both LtCDKA1;1 mRNA and protein are most evident in floret meristems. Only ~10% of cells within the apical dome are dividing at any time but the LD increase in LtCDKA1;1 may reflect an early transient increase in the mitotic index (Jacqmard et al. 1993) as well as a later increase when spikelet primordia form. Increased expression of an AP1-like gene (LtMADS2) follows that of LtCDKA1;1. Overall, LtCDKA1;1 is a useful marker of both early florigenic signalling and of later morphological/developmental aspects of the floral transition.

Shoot Apex Sugars in Relation to Long-Day Induction of Flowering in Lolium temulentum L

1991 ◽  
Vol 18 (2) ◽  
pp. 121 ◽  
Author(s):  
RW King ◽  
LT Evans
Keyword(s):  
Flux Density ◽  
Shoot Apex ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Sucrose Content ◽  
Inflorescence Development ◽  
Lolium Temulentum ◽  
Long Day ◽  
Floral Evocation

Inflorescence initiation in Lolium temulentum is induced by a single long day with a photoperiod extension of 16 h under low photon flux density (12 μmol PAR m-2 s-1) from incandescent lamps. Under these conditions the content of sucrose, the predominant free sugar in the shoot apex, fluctuates diurnally in the same way as in short day apices. There was no evidence of a greater apical sucrose content at any time during the long day or in the following period of high irradiance when floral evocation occurs. Thereafter, however, the diurnal fluctuation in apical sucrose content became more pronounced. Increasing the sugar supply to the apex by raising the photon flux density during the daily light period did not lead to flowering of non-induced plants; nor did the high contents of apical sugars reached in apices cultured in vitro on 5% sucrose medium. By contrast, when apices were excised after receipt of the floral stimulus from long day leaves, increase in the sugar content enhanced inflorescence development in vitro, this response being most pronounced after the inflorescences were initiated. Thus, floral evocation in L. temulentum does not require an increase in the content of sucrose at the apex although inflorescence development is highly responsive to it. When photoperiodic extensions with incandescent or fluorescent lamps were compared for their effects on apical sugars and flowering response, there was no interaction between light quality and photon flux density. Thus the shoot apex response to the low irradiance, photoperiodic time-measurement processes of leaves is distinct from the apical response to sugar supply. In Lolium temulentum floral evocation is controlled by the photoperiodic processes, the response to which is amplified by high sugar supplies but not replaced as it is in Sinapis alba.

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