Elevation in the Sucrose Content of the Shoot Apical Meristem of Sinapis alba at Floral Evocation

Nanogram tissue samples from apical meristems of Sinapis alba were assayed for sucrose, total soluble hexosyl equivalents ( glucose and fructose plus hexoses from sucrose hydrolysis), and total soluble glucosyl equivalents ( glucose plus glucose from sucrose hydrolysis). On dry weight basis, sucrose concentration increased by more than 50% within 10 hours after the start of either a long photoperiod or a short photoperiod displaced by 10 hours in the 24-hour cycle (`displaced short day'). (These treatments induce flower initiation) Glucose and fructose concentrations were close to zero in vegetative meristems and remained low compared to sucrose in meristems of induced plants. Within a single meristem, the peripheral and the central zones had similar concentrations of sucrose. Our results indicate that an early physiological event in floral transition is the accumulation of sucrose in the meristem.     

Changes in the Protein Composition of the Shoot Apical Bud of Sinapis alba in Transition to Flowering

Vegetative plants of Sinapis alba L. grown in short days were induced to flower by expsoure to one or continuous long days. In both inductive conditions, the first flowers were initiated about 60 h after the start of the treatment. Soluble protein extracts were prepared from apical buds and just-expanded leaves of both vegetative and induced plants. Rabbit antisera were prepared using extracts from vegetative and reproductive buds. Immunodiffusion tests were performed. Analysis of the precipitin bands indicated that: (1) one antigenic protein was present in the vegetative buds and disappeared from the buds of induced plants between 96 and 240 h after the start of the inductive treatment; (2) the concentration of a another antigenic protein increased in buds of induced plants 30 h after the start of the inductive treatment; (3) the concentration of a third antigenic proteín increased in buds of induced plants at 96 h.     

Changes to Proteins in the Shoot Meristem of Silene coeli-rosa during the Transition to Flowering

Changes in proteins were measured to test whether they werelinked to flowering, the cell cycle or both in Silene coeli-rosashoot apices. Seeds were germinated and grown at 20?C in shortdays (SD) of 8 h light from fluorescent and tungsten (F + T)/16hdarkness for 28 days (day 0). Plants were then exposed to: 7long days (LD)+2 SD (inductive), 7 LD + 48 h darkness (inductive)or 7 dark-interrupted (di) LD + 2SD (non-inductive), where eachLD and diLD comprised 8 h F + T/16 h T, 8 h F+T/l h darkness/15h T, respectively. There were no qualitative differences inpolypeptide composition in the LD and SD treatments on days0, 5, 6 and 7 but 60 new polypeptides were detected on LD₈ andsome modifications in the intensity of common spots also occurred.These qualitative and quantitative changes were not alteredfollowing 7 LD + 48 h darkness, which is known to suppress synchronisationof the cell cycle but not flowering. Thus, changes on day 8are linked to flowering. Transient increases in protein perunit area were detected in prophase cells on days 0, 3, 4 whilesustained increases occurred on days 7 and 8. The changes ondays O, 3 and 4 were suppressed by the diLD treatment. Thus,quantitative changes to proteins, co-inciding with known LD-inducedchanges to the cell cycle, are linked to flowering. (Received April 2, 1990; Accepted September 12, 1990)     

Cytophotometric Study of the 2C Nuclear DNA Content in the Apical Bud of Sinapis alba during Floral Transition

Feulgen cytophotometry was used to detect possible changes inthe 2C DNA content in the various parts of the apical bud ofSinapis alba during floral evocation and flower development.This study showed that there was no significant difference inthe 2C DNA content between the vegetative, evoked or reproductivemeristems. In vegetative plants, the 2C DNA content was lowerin the leaf primordia than in the meristem. This content inthe leaf exhibited a further decrease during the floral transition.In the flower primordia, the 2C value never exceeded the typicalvalue of the meristem. In the flower at anthesis, the DNA contentwas lower in the pistil and stamen than in the meristem. Apical bud, floral transition, 2C DNA content, cytophotometry, Sinapis alba L.     

Variation in the Rate of Cell Division in the Apical Meristem of Sinapis alba During Transition to Flowering

Rates of cell division in the central and the peripheral zonesof vegetative and evoked meristems of Sinapis alba have beenmeasured by accumulation of metaphases after colchicine treatment.The cells of the central zone had a longer cycle than the cellson the flanks of both kinds of meristems. The duration of thecell cycle was shortened in both zones of the meristem duringtransition to flowering. It was shown that the mitotic indicesof the two regions of the meristem were closely comparable totheir rates of cell division and therefore could be consideredrepresentative of the rates of cell division.     

Levels and Ultrastructural Localization of Calcium in Sinapis alba during the Floral Transition

Atomic absorption spectrophotometry was used to determine thetotal amount of Ca in the leaves and apical bud of the long-dayplant Sinapis alba during the floral transition induced by asingle long day. The level of Ca increased in the apical budbut did not change significantly in the leaves. Ca was furtherlocalized cytochemically and measured in the meristem cellsby X-ray microprobe analysis. In the meristem, the level ofCa was found to increase in all cellular compartments, but mainlyin the nucleolus. The results are discussed in relation to otherevents that are known to occur in the meristem during the floraltransition. (Received July 19, 1988; Accepted January 24, 1989)     

Cadmium Induced Ultrastructural Changes in Shoot Apical Meristem of Elodea Canadensis Rich.

The ultrastructure of cells of ground meristem in the peripheral zone of shoot apical meristem in Elodea canadensis Rich. was studied after treatment with cadmium in concentrations 0.5, 1, 2, 3, 5, and 6 g(Cd²⁺) m⁻³. After 5 d treatment, changes in the structural organisation of the plastid apparatus were found, namely in proplastid, amyloplast, and amoeboid stages of plastid development. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rates of Cell Division in the Shoot Apical Meristem of Pisum

The relative rates of cell division in different regions ofthe pea shoot apical meristem were obtained by measuring theincrease in the numbers of metaphases following applicationof colchicine to the plants. Absolute values for the rates ofcell division could be calculated since the average rate ofcell division for the whole apex was known. Measurements ofthe rates of cell division were obtained at defined intervalsduring the course of a single plastochron. Within each regionof the apex the rate of cell division did not change more thanabout two-fold throughout the plastochron. There was very littleor no increase in the rate of cell division associated withleaf initiation. The formation of a leaf primordium and thesubsequent growth of the apical dome apparently result fromchanges in the direction of growth rather than changes in therates of growth. Three main regions were discernible withinthe apical meristem: a region with a slow rate of cell divisionin the apical dome, a region of a faster rate of cell divisionat the base of the apical dome and at the site of initiationof procambial strands, and a region of an intermediate rateof cell division in the newly initiated leaf primordium andthe adjacent part of the shoot axis.     

被子植物的茎端分生组织及其细胞的命运

茎端分生组织的活动是植物地上部分所有器官的来源,在植物个体发育过程中具有重要作用.介绍了茎端分生组织的基本形态、起始与维持的分子基础及其衍生细胞的命运.     

Cell Differentiation and Organ Initiation at the Shoot Apical Meristem

Plants continuously generate organs at the flanks of their shoot apical meristems (SAMs). The patterns in which these organs are initiated, also called patterns of phyllotaxis, are highly stereotypic and characteristic for a particular species or developmental stage. This stable, predictable behaviour of the meristem has led to the idea that organ initiation must be based on simple and robust mechanisms. This conclusion is less evident, however, if we consider the very dynamic behaviour of the individual cells. How dynamic cellular events are coordinated and how they are linked to the regular patterns of organ initiation is a major issue in plant developmental biology.     

植物茎端分生组织中的茎干细胞调控机制

介绍了高等植物茎端分生组织茎干细胞维持自我更新和产生分化细胞之问平衡的分子机制研究进展.     

Changes in the Pattern of Cell Division in the Shoot and Root Meristems of Lolium perenne during the Transition from Vegetative to Floral Growth

For Lolium perenne cv. Cropper, a system which resulted in 100%flowering comprised 90 short days (SD) at 4 ?C (vernalization)and 30 SD at 18 ?C followed by 8 long days (LD). The mitoticindex and G1 and G2 percentages were measured in the shoot androot apices of plants following 2, 5 or 8 LD and in SD controlssampled at the beginning and end of induction. Identical measurementswere made in plants given 48 SD at 18 ?C followed by 2, 5 or8 LD; plants remained vegetative in response to this treatmentlacking vernalization. Significant increases in both mitoticindex and meristem size occurred in the shoot apex in LD followingthe vernalizing, but not the non-vernalizing, treatment. A clusterof mitoses in the apical dome of the shoot apex was unique tothe vernalized plants given 5 or 8 LD. However, an increasein root meristem size occurred regardless of vernalization,but a significant increase in the mitotic index was limitedto vernalized plants given 5 or 8 LD. Whilst the vernalization-LDtreatment resulted in an increase in the G2 percentage in theshoot apex following 2, 5 or 8 LD, no such alteration was observedin the root meristem. Thus, the changes to the cell cycle whichcorrelated with flowering were increased mitotic indices andG2 percentages in the shoot apex at each sampling time and increasedmitotic indices in the root apex following 5 and 8 LD. Key words: Cell division, flowering, Lolium perenne L.     

New Evidence for the Role of Mechanical Forces in the Shoot Apical Meristem

Abstract The mechanism for initiation of lateral organs in the shoot apical meristem is still unknown. In this article we investigate one critical component of a buckling mechanism of organ initiation (that is, the presence and distribution of compressive stresses in the meristem). Direct evidence for compression in the sunflower capitulum was obtained from the gaping pattern of shallow cuts and the propagation of fractures. Cuts gaped widely in the central region of the capitulum but remained closed, or nearly so, in the generative and differentiation regions, suggesting the presence of circumferential compression at these locations. Fractures were initiated in the generative region and propagated circumferentially over most of their length. They did not cross the generative region perpendicularly, suggesting again the presence of compressive stresses in the circumferential direction. This conclusion was confirmed by the stress distribution computed from the geometry of the capitulum at three stages of development. One interpretation of these results is that the generative region corresponds to a zone of compression that could control the initiation of new primordia by means of buckling of the tunica layer. Received 12 January 2000; accepted 2 February 2000     

Cytokinin as a Possible Component of the Floral Stimulus in Sinapis alba

Results of previous investigations indicated that one of the early and essential events occurring in the apical meristem of Sinapis alba L. during the transition to flowering is the release to mitosis of the G₂ nuclei; the trigger to mitosis is generated in the leaves and its movement out of the leaves begins around 16 hours after the start of the inductive treatment. The mitotic wave in the meristem culminates 10 hours later.