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1.
Summary The plasmodesmal network was examined in multicellular protoplast-derived calluses of the dicotyledonSolanum nigrum which had not yet formed any visible adventitious organs and in globular proembryogenic structures developed from scutellar calluses of the monocotyledonMolinia caerulea. Electron microscopical analyses revealed that both calluses and proembryos consisted of small, undifferentiated cells. The interconnecting plasmodesmata at many cell interfaces were structurally inconspicuous in both systems; in particular cell walls, however, all plasmodesmata were occluded with an osmiophilic, dense material. As the blocking material was obviously located in the microchannels of the plasmodesmal cytoplasmic sleeves, the plugged plasmodesmata can be assumed to be nonfunctional. Thus, selective occlusion of all the plasmodesmata in specific cell walls resulted in the symplasmic disconnection of particular adjacent cells. Complex patterns of symplasmic continuity and discontinuity were established within the developing tissues. Some cells or groups of cells were entirely symplasmically disconnected from the surrounding cells by plugged plasmodesmata and might function as independent domains. However, blockage of plasmodesmata was achieved by the surrounding cells rather than by those cells belonging to the isolated domains. The demarcation of symplasmic domains might be a general prerequisite for differential morphogenesis, since they were found to be established very early in the course of morphogenetic processes. 相似文献
2.
Physiological elevations in cytoplasmic free calcium by cold or ion injection result in transient closure of higher plant plasmodesmata 总被引:7,自引:0,他引:7
The concentration of cytoplasmic free calcium ([Ca2+]cyt) required to close higher plant plasmodesmata was investigated using corn (Zea mays L. cv. Black Mexican Sweet) suspension-culture cells. Physiological elevations of [Ca2+]cyt were applied by cold treatment, and ion injection was also used to increase [Ca2+]cyt, by diffusion (for small increases) or by iontophoresis (for larger increases). The impact of such treatments on [Ca2+]cyt was measured by ratiometric ion imaging. Intercellular communication during treatments was monitored using our recently developed
electrophysiological technique that allows the electrical resistance of plasmodesmata and the plasma membranes of a sister-cell
pair to be measured. A 4-fold increase in the calculated resistance of single plasmodesmata was observed in response to cold
treatment that caused a 2-fold increase in average [Ca2+]cyt (from 107 to 210 nM). In response to iontophoresis of Ca2+, plasmodesmata were observed to go from “open” (low resistance) to “shut” (high resistance) and then back “open” within 10 s.
Our results thus indicate that higher plant plasmodesmata respond quickly to physiological changes in [Ca2+]cyt.
Received: 2 June 1999 / Accepted: 16 July 1999 相似文献
3.
Microtubule organization plays an important role in plant morphogenesis; however, little is known about how microtubule arrays
transit from one organized state to another. The use of a genetically incorporated fluorescent marker would allow long-term
observation of microtubule behavior in living cells. Here, we have characterized a Nicotiana tabacum L. cv. Bright Yellow 2 (BY-2) cell line that had been stably transformed with a gfp-mbd construct previously demonstrated to label microtubules (J. Marc et al., 1998, Plant Cell 10: 1927–1939). Fluorescence levels
were low, but interphase and mitotic microtubule arrays, as well as the transitions between these arrays, could be observed
in individual gfp-mbd-transformed cells. By comparing several attributes of transformed and untransformed cells it was concluded that the transgenic
cells are not adversely affected by low-level expression of the transgene and that these cells will serve as a useful and
accurate model system for observing microtubule reorganization in vivo. Indeed, some initial observations were made that are
consistent with the involvement of motor proteins in the transition between the spindle and phragmoplast arrays. Our observations
also support the role of the perinuclear region in nucleating microtubules at the end of cell division with a progressive
shift of these microtubules and/or nucleating activity to the cortex to form the interphase cortical array.
Received: 2 June 1999 / Accepted: 13 August 1999 相似文献
4.
Frequency, density and branching of plasmodesmata were counted in successive tangential and transverse walls in the cambial
zone of tomato stems in order to examine development of the plasmodesmal network in a chronological order. Coincident with
progress of cell development, plasmodesmal connectivity increased, both at the xylem- and phloem-side. In transverse walls,
the number of secondary plasmodesmata enhanced considerably. The same held for tangential walls, with a superimposed plasmodesmal
doubling during the first phase of phloem development. This plasmodesmal doubling was interpreted to result from the deposition
of wall material between branched plasmodesmal strands. Structural plasmodesmal development was correlated with production
of hydroxyl radicals which control local cell wall alterations. Successive phases of plasmodesmal deployment and modification
were distinguished which may coincide with differential functional capacities as documented by intracellular injection of
fluorochromes. Diffusion-driven symplasmic transport appeared to be transiently interrupted during cell maturation. 相似文献
5.
Summary In the multicellular organisms of higher plants, plasmodesmata provide pathways for intimate symplasmic communication between
neighboring cells. The arguments summarized in the present review demonstrate that plasmodesmata are diverse and highly dynamic
structures. Differences in the plasmodesmal origin and modifications of the plasmodesmal structure and functioning at the
various cell interfaces are the basic means which give rise to a complicated and flexibile symplasmic network. This complex
communication system is discussed to serve a significant role in the coordinated development and in the concerted physiological
functioning of the cells within the plant tissues, organs, and organisms. 相似文献
6.
Minor-vein ultrastructure and sugar export were studied in mature summer and winter leaves of the three broadleaf-evergreen species Ajuga reptans var. artropurpurescens L., Aucuba japonica Thunb. and Hedera helix L. to assess temperature effects on phloem loading. Leaves of the perennial herb Ajuga exported substantial amounts of assimilates in form of raffinose-family oligosaccharides (RFOs). Its minor-vein companion cells represent typical intermediary cells (ICs), with numerous small vacuoles and abundant plasmodesmal connectivity to the bundle sheath. The woody plants Hedera and Aucuba translocated sucrose as the dominant sugar species, and only traces of RFOs. Their minor-vein phloem possessed a layer of highly vacuolated cells (VCs) intervening between mesophyll and sieve elements. Depending on their location and ontogeny, VCs were classified either as companion or parenchyma cells. Both cell types showed symplasmic continuity to the adjacent mesophyll tissue although at a lower plasmodesmal frequency compared to the Ajuga ICs. p-Chloromercuribenzenesulfonic acid did not reduce leaf sugar export in any of the plants, indicating a symplasmic mode of phloem loading. Winter leaves did not show symptoms of frost injury, and the vacuolar pattern in ICs and VCs was equally prominent in both seasons. Starch accumulation as a result of reduced phloem loading was not observed to be triggered by low temperature. In contrast, high amounts of starch were found in mesophyll and bundle-sheath cells of summer leaves. Physiological data on season-dependent leaf exudation showed the maintenance of sugar export in cold-acclimated winter leaves. 相似文献
7.
胞间连丝研究的进展 总被引:6,自引:0,他引:6
胞间连丝为多细胞植物有机体提供了一个直接的细胞间物质运输和信息传递的细胞质通道,把一个个独立的“细胞王国”转变成相互连接的共质体,它是当今细胞生物学中十分活跃的研究领域。日益增多的研究结果揭示,胞间连丝协调基因表达和许多的细胞生理生化过程,对细胞的分裂与分化、形态发生、植物体的生长与发育,以及植物对环境的反应与适应等诸方面都起着十分重要的作用。本文仅就胞间连丝结构的多样性;胞间通道的调节因子;大分子蛋白质和核酸的胞间运输;胞间连丝阻断和共质体分区的形成及其与形态发生、休眠和抗逆性的关系等几个方面的新进展做一个简要的综述,借此例证胞间连丝在植物生命活动中的重要意义。 相似文献
8.
Leaf and minor vein structure were studied in Arabidopsis thaliana (L.) Heynh. to gain insight into the mechanism(s) of phloem loading. Vein density (length of veins per unit leaf area) is
extremely low. Almost all veins are intimately associated with the mesophyll and are probably involved in loading. In transverse
sections of veins there are, on average, two companion cells for each sieve element. Phloem parenchyma cells appear to be
specialized for delivery of photoassimilate from the bundle sheath to sieve element-companion cell complexes: they make numerous
contacts with the bundle sheath and with companion cells and they have transfer cell wall ingrowths where they are in contact
with sieve elements. Plasmodesmatal frequencies are high at interfaces involving phloem parenchyma cells. The plasmodesmata
between phloem parenchyma cells and companion cells are structurally distinct in that there are several branches on the phloem
parenchyma cell side of the wall and only one branch on the companion cell side. Most of the translocated sugar in A. thaliana is sucrose, but raffinose is also transported. Based on structural evidence, the most likely route of sucrose transport is
from bundle sheath to phloem parenchyma cells through plasmodesmata, followed by efflux into the apoplasm across wall ingrowths
and carrier-mediated uptake into the sieve element-companion cell complex.
Received: 5 October 1999 / Accepted: 20 November 1999 相似文献
9.
胞间连丝为多细胞植物有机体提供了一个直接的细胞间物质运输和信息传递的细胞质通道,把一个个独立的“细胞王国”转变成相互连接的共质体,它是当今细胞生物学中十分活跃的研究领域。日益增多的研究结果揭示,胞间连丝协调基因表达和许多的细胞生理生化过程,对细胞的分裂与分化、形态发生、植物体的生长与发育,以及植物对环境的反应与适应等诸方面都起着十分重要的作用。本文仅就胞间连丝结构的多样性;胞间通道的调节因子;大分子蛋白质和核酸的胞间运输;胞间连丝阻断和共质体分区的形成及其与形态发生、休眠和抗逆性的关系等几个方面的新进展做一个简要的综述,借此例证胞间连丝在植物生命活动中的重要意义。 相似文献
10.
A. Schulz 《Protoplasma》1995,188(1-2):22-37
Summary Root tips ofPisum sativum seedlings were exposed to 350 mM mannitol, which was shown to effect a transient but dramatic increase in phloem unloading, and investigated by electron microscopy. After chemical fixation and embedding, extremely thin sections of the root extension zone were examined. Outer, inner, and desmotubule diameters of 830 primary plasmodesmata in transverse walls of cortical cells were measured. Statistical analysis indicated that the majority of plasmodesmata had no neck constriction during osmoregulation. Compared to controls, a highly significant increase in mean plasmodesmata diameter was found, but the desmotubule diameter remained unchanged. Both loss of neck constriction and widening of the cytoplasmic sleeve indicate an increase in effective passage area of plasmodesmata. Spokes between plasma membrane and desmotubule were preserved. Continued exposure of the root tips to mannitol led to a return to control values for plasmodesmal diameters. In contrast to these responses, plasmolysis of cortical cells by 1,000 mM sucrose, diminishing phloem unloading, was accompanied by a reduction in those plasmodesmata classified as open. This is the first report showing a correlation between the ultrastructure of plasmodesmata and the rate of symplasmic transport. The role of the different plasmodesmal components in controlling the passage area of symplasmic transport is discussed. 相似文献
11.
Batch cultures of photoautotrophic cell suspensions of Chenopodiumrubrum L., growing in an inorganic medium on CO2 under a daily balanced light–dark regime of 16 : 8 h could be maintained for approximately 100 d without subcultivation.
The long-lived cultures showed an initial cell division phase of 4 weeks, followed by a stationary phase of another 4 weeks,
after which ageing and progressive cell death reduced the number of living cells and the cultures usually expired after another
3–4 weeks. These developmental phases of the cell culture were characterised with respect to photosynthetic performance, dark
respiration, content of phytohormones and capacity of cell division. Cell division of the majority of the cells finished in
the G1- or G0-phase of the cell cycle, caused by a pronounced decline in the endogenous levels of auxin and cytokinins. Supply
of these growth factors to resting cells resulted in resumption of cytokinesis, at least by some of the cells. However, responsiveness
to the phytohomones declined during the stationary phase, and subcultivation was no longer possible beyond day 60 when the
phases of ageing and death commenced. Ageing was characterised by a further decline in the photosynthetic capacity of the
cells, by a climacteric enhancement of dark respiration, but also by a slight increase in the level of IAA and cytokinins
concomitant with a decrease in ethylene. Similarities and differences between the development of batch-cultured photoautotrophic
cells of C. rubrum and that of a leaf are discussed with respect to using the cell culture as a model for a leaf.
Received: 30 April 1999 / Accepted: 21 August 1999 相似文献
12.
The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well
as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem.
The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since
they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity,
and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the
wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al.
1998, Plant cell proliferation and its regulation in growth and development, pp. 67–78; Wiley), and (ii) the increase in frequency
of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating
the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell
plate during mitosis and are thus of secondary origin.
Received: 4 October 1999 / Accepted: 23 December 1999 相似文献
13.
From the cambial stage onwards, the symplasmic autonomy of sieve element/companion cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intracellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multicellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.Abbreviations LYCH
Lucifer Yellow CH
-
membrane potential
- PMF
proton-motive force
- PP
phloem parenchyma cell
- SE/CC-complex
sieve element/companion cell complex
- SR-G
sulphorhodamine G 相似文献
14.
We used a genetic assay to monitor the behavior of sister chromatids during the cell cycle. We show that the ability to induce
sister chromatid exchanges (SCE) with ionizing radiation is maximal in budded cells with undivided nuclei and then decreases
prior to nuclear division. SCE can be induced in cells arrested in G2 using either nocodazole or cdc mutants. These data show that sister chromatids have two different states prior to nuclear division. We suggest that the
sister chromatids of cir. III, a circular derivative of chromosome III, separate (anaphase A) prior to spindle elongation
(anaphase B). Other interpretations are also discussed. SCE can be induced in cdc mutants that arrest in G2 and in nocodazole-treated cells, suggesting that mitotic checkpoints arrest cells prior to sister
chromatid separation.
Received: 3 July 1996 / Accepted: 4 October 1996 相似文献
15.
Tomato (Lycopersicon esculentum Mill.) prosystemin in fusion with a viral signal peptide was expressed in Sf21 insect cell cultures after infection with recombinant baculoviruses. Prosystemin was purified from culture supernatants
and its identity was confirmed by N-terminal sequence and mass-spectral analyses. Recombinant prosystemin was found to be
equally active as compared to systemin in inducing the expression of wound-response genes in tomato plants. In cultured cells
of L. peruvianum, prosystemin elicited a rapid alkalinization of the growth medium. The timing and dose-dependence of the alkalinization response
were found to be identical for prosystemin and systemin, respectively. Prosystemin-triggered defense responses were inhibited
by a competitive antagonist of systemin activity, indicating that the systemin sequence within the primary structure of prosystemin
determines its activity.
Received: 30 August 1999 / Accepted: 6 December 1999 相似文献
16.
Summary. Hepatocytes were cultured for 3 days as spheroids (aggregates) or as monolayers in basal medium and in sulfur amino acid-supplemented
media. Cultured hepatocytes had low levels of cysteine dioxygenase (CDO) activity and normal levels of γ-glutamylcysteine
synthetase (GCS) and cysteinesulfinate decarboxylase (CSDC) activities compared to freshly isolated cells. CDO activity increased
and GCS activity decreased in a dose-response manner in cells cultured in either methionine- or cysteine-supplemented media.
CSDC activity was not significantly affected by methionine supplementation. Changes in CDO and GCS were associated with changes
in cysteine catabolism to taurine plus sulfate and in synthesis of glutathione, respectively. These responses are similar
to those observed in liver of intact rats fed diets supplemented with sulfur amino acids. A near-maximal response of CDO or
GCS activity was observed when the medium contained 1.0 mmol/L of methionine plus cyst(e)ine. Changes in CDO and GCS activities
did not appear to be mediated by changes in the intracellular glutathione concentration. Cultured hepatocytes offer a useful
model for further studies of cysteine metabolism and its regulation in response to sulfur amino acid availability.
Received June 2, 1999/Accepted September 16, 1999 相似文献
17.
N.E. El Houssif 《Journal of mathematical biology》2001,42(5):424-438
In this paper we model the population dynamics of the worm Nais elinguis, which reproduces by division into two unequal parts. By using renewal theory we derive the asymptotic behaviour of a Naidis elinguis population. In particular we prove a certain relation between the fraction of the population that was born small (respectively
the fraction that was born large) and the inter-division times.
Received 20 January 1999 / Revised version: 1 August 1999?Published online: 10 April 2001 相似文献
18.
The shoot apical meristem restores its symplasmic organization during chilling-induced release from dormancy 总被引:13,自引:0,他引:13
Päivi L. H. Rinne Päivi M. Kaikuranta Christiaan van der Schoot 《The Plant journal : for cell and molecular biology》2001,26(3):249-264
The shoot apex of overwintering perennials ceases its morphogenetic activity at the end of the growing season and transforms into a bud which is dormant and freezing-tolerant. In birch (Betula pubescens) these events are triggered by short photoperiod, and involve the production of 1,3-beta-D-glucan containing sphincters on the plasmodesmata. As a result, all symplasmic pathways shut down. Here we show that breakage of bud dormancy by chilling involves restoration of the symplasmic organization of the meristem. This restoration is likely to be mediated by 1,3-beta-D-glucanase, which was present in small spherosome-like vacuoles that arose de novo during dormancy induction. During chilling these vacuoles were displaced from the bulk cytoplasm to the cortical cytoplasm where they became aligned with the plasma membrane, often associated with plasmodesmata. At this stage the enzyme also appeared outside the vacuoles. During chilling, 1,3-beta-D-glucan disappeared from the plasmodesmal channels and wall sleeves, and the plasmodesmata regained the capacity for cell-cell transport, as demonstrated by microinjection of Lucifer Yellow CH and Fluorescein-tagged gibberellic acid. Collectively, the present experiments demonstrate that restoration of the symplasmic organization of the meristem is indispensable for the release of buds from dormancy and the assumption of a proliferation-competent state, and implicate 1,3-beta-D-glucanase action at the plasmodesmata. Based on these findings we propose a model for 'dormancy cycling' which depicts the meristem as passing through three sequential states of cellular communication with characteristic sensitivities to distinct environmental cues. 相似文献
19.
Ermel FF Follet-Gueye ML Cibert C Vian B Morvan C Catesson AM Goldberg R 《Planta》2000,210(5):732-740
The development of pectin structural features during the differentiation of cambial derivatives was investigated in aspen
(Populus tremula L. × P. tremuloides Michx.) using biochemical and immunocytochemical methods. Comparisons were also made between active and resting tissues.
Active tissues, in particular cambial cells and phloem derivatives, were characterized by a high pectin content. Use of antibodies
raised against arabinan side chains of rhamnogalacturonan 1 (LM6), as well as biochemical analysis, revealed an obvious decrease
from the cortex to the differentiating xylem. Galactan side chains, detected with LM5 antibodies, were present mainly in the
cambial zone and enlarging xylem cells. In contrast, they were totally absent from sieve-tube cell walls. Image analysis of
LM5 immunogold labelling in the cambial zone showed a clustered distribution of galactan epitopes in the radial walls, a distribution
which might result from the association of two different periodic processes, namely the exocytosis of galactan and wall expansion.
Cessation of cambial activity was characterized by cell wall thickening accompanied by a sharp decrease in the relative amount
of pectin and a lowering of the degree of methylesterification. The data provide evidence that the walls of phloem and xylem
cells differ in their pectin composition even at a very early stage of commitment. These differences offer useful tools for
identifying the initial cells among their immediate neighbours.
Received: 12 June 1999 / Accepted: 20 October 1999 相似文献
20.
Intracellular chloroplast photorelocation in the moss Physcomitrella patens is mediated by phytochrome as well as by a blue-light receptor 总被引:3,自引:0,他引:3
The light-induced intracellular relocation of chloroplasts was examined in red-light-grown protonemal cells of the moss Physcomitrella patens. When irradiated with polarized red or blue light, chloroplast distribution in the cell depended upon the direction of the
electrical vector (E-vector) in both light qualities. When the E-vector was parallel to the cross-wall (i.e. perpendicular
to the protonemal axis), chloroplasts accumulated along the cross-wall; however, no accumulation along the cross-wall was
observed when the E-vector was perpendicular to it (i.e. parallel to the protonemal axis). When a part of the cell was irradiated
with a microbeam of red or blue light, chloroplasts accumulated at or avoided the illumination point depending on the fluence
rate used. Red light of 0.1–18 W m−2 and blue light of 0.01–85.5 W m−2 induced an accumulation response (low-fluence-rate response; LFR), while an avoidance response (high-fluence-rate response;
HFR) was induced by red light of 60 W m−2 or higher and by blue light of 285 W m−2. The red-light-induced LFR and HFR were nullified by a simultaneous background irradiation of far-red light, whereas the
blue-light-induced LFR and HFR were not affected at all by this treatment. These results show, for the first time, that dichroic
phytochrome, as well as the dichroic blue-light receptor, is involved in the chloroplast relocation movement in these bryophyte
cells. Further, the phytochrome-mediated responses but not the blue-light responses were revealed to be lost when red-light-grown
cells were cultured under white light for 2 d.
Received: 7 September 1999 / Accepted: 15 October 1999 相似文献