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1.
To understand the role of microtubules in the regulation of cell elongation, we characterized microtubule patterns in fass, a cell shape mutant of Arabidopsis thaliana (L.) Heynh. Examining microtubule patterns via immunocytochemistry, we found that fass cells were able to organize their microtubules into mitotic spindles and phragmoplasts. During interphase or preprophase,
fass cells had cortical microtubules, verified by transmission electron microscopy, but these microtubules were not organized
into the cortical array or preprophase band. Using chromatin condensation and tubulin localization on the nuclear envelope
as preprophase stage markers, we found that although fass cells lacked the preprophase band and cortical array, their cell division cycle appeared normal. To pinpoint the defect in
fass cells, we delineated the sequential events leading to cortical array formation in Arabidopsis cells and found that fass cells initiated and recolonized cortical microtubules in the same manner as wild-type cells, but failed to order them into
the cortical array. Taken together, these results suggest fass cells are impaired in a component of the microtubule organizing center(s) required for the proper ordering of cortical microtubules
at the plasma membrane.
Received: 23 August 1996 / Accepted: 25 September 1996 相似文献
2.
A cytoskeletal basis for wood formation in angiosperm trees: the involvement of microfilaments 总被引:3,自引:0,他引:3
The cortical microfilament (MF) component of the cytoskeleton within axial elements of the secondary vascular system of the
angiosperm tree, Aesculus hippocastanum L. (horse-chestnut) was studied using transmission electron microscopy of ultrathin sections and indirect immunofluorescence
microscopy of actin in thick sections. As seen by electron microscopy, MF bundles have a net axial orientation within fusiform
cambial cells and their secondary vascular derivatives (i.e. in the axial xylem and phloem parenchyma, xylem fibres, vessel
and sieve elements, and companion cells). Immunofluorescence studies, however, reveal that this axial orientation can be more
accurately described as a helix of extremely high pitch; it is a persistent feature of all axial secondary vascular elements during their development. Helical MF arrays are the only arrangement seen in secondary
phloem cells. However, in addition to helices, other MF arrays are seen in secondary xylem cells. For example, fibres possess
ellipses of MFs associated with simple-pit formation, and vessel elements possess circular arrays of MFs that associate with
the developing inter-vessel bordered pits, ray–vessel contact pits, and with the perforation plate. Linear MF arrays are seen
co-oriented with the developing tertiary wall-thickenings in vessel elements. The possible roles of MFs during the cytodifferentiation
of secondary vascular cells is discussed, and compared with that of microtubules.
Received: 7 June 1999 / Accepted: 23 December 1999 相似文献
3.
Complexes of microtubules, vesicles, and (to varying degrees) dense matrix material around the microtubules were seen along the edges of cells in root apices of Azolla pinnata R.Br. (viewing the cells as polyhedra with faces, vertices and edges). They are best developed after cytokinesis has been completed, when the daughter cells are reinstating their interphase arrays of microtubules. They are not confined to edges made by the junction of new cell plates with parental walls, but occur also along older edges. Similar matrices and vesicles are seen amongst phragmoplast microtubules and where pre-prophase bands intersect the edges of cells. It is suggested that the complexes participate in the development of cortical arrays of microtubules. The observations are combined with others, made on pre-prophase bands and on the substructure of cortical arrays lying against the faces of cells, to develop an hypothesis on the development of cortical microtubules, summarised below: Microtubules are nucleated along the edges of cells, at first growing in unspecified orientations and then becoming bridged to the plasma membrane. Parallelism of microtubules in the arrays arises by inter-tubule cross-bridging. Lengths of microtubule are released from, or break off, the nucleating centres and are moved out onto the face of the cell by intertubule and tubule-membrane sliding, thus accounting for the presence there of short tubules with randomly placed terminations. The nucleating zones along cell edges might have vectorial properties, and thus be able to control the orientation of the microtubules on the different faces of the cell. Also, localised activation could generate localised arrays, especially pre-prophase bands in specified sites and planes. Two possible reasons for the spatial restriction of nucleation to cell edges are considered. One is that the geometry of an edge is itself important; the other is that along most cell edges there is a persistent specialised zone, inherited at cytokinesis by the daughter cells when the cell plate bisects the former pre-prophase-band zone. 相似文献
4.
In protoplast-derived Solanum nigrum microcalluses, plasmodesmal connectivity and cell division behaviour of the sister cells were examined by repeated pressure-injection
experiments with the fluorescent dye Lucifer Yellow (LYCH; Mr 457) and concomitant light-microscopical long-term live observations. The studies revealed that the plasmodesmal permeability
of the cultured cells differs in the distinct stages of microcallus development. There was a correlation between the symplasmic
connectivity of the cells and the synchronousness of their mitotic activity. Sister cells which were symplasmically interconnected
by functional plasmodesmata, permitting the diffusion of LYCH, were always found to divide synchronously. However, asynchronous
mitotic divisions were exclusively observed in those sister cells whose plasmodesmata were closed to LYCH. The temporary symplasmic
isolation is presumably performed by reversible gating of plasmodesmata. Repeated dye-coupling experiments on the same microcalluses
showed that symplasmically interconnected sister cells may become uncoupled and vice versa, according to their division behaviour.
These findings on cultured cells indicate that modulation of the symplasmic connectivity determines the synchronization of
mitotic activity. Yet it remains to be proven whether this is true in planta as well. The results are discussed with respect
to the possible role of plasmodesmata in exerting “supracellular control” over mitotic activity by trafficking mitosis-regulating
signals.
Received: 6 March 1999 / Accepted: 14 July 1999 相似文献
5.
High-efficiency induction of soybean hairy roots and propagation of the soybean cyst nematode 总被引:8,自引:0,他引:8
Cotyledon explants of 10 soybean [Glycine max (L.) Merr.] cultivars were inoculated with Agrobacterium rhizogenes strain K599 with and without binary vectors pBI121 or pBINm-gfp5-ER possessing both neomycin phosphotransferase II (nptII) and β-glucuronidase (gus) or nptII and green fluorescent protein (gfp) genes, respectively. Hairy roots were produced from the wounded surface of 54–95% of the cotyledon explants on MXB selective
medium containing 200 μg ml−1 kanamycin and 500 μg ml−1 carbenicillin. Putative individual transformed hairy roots were identified by cucumopine analysis and were screened for transgene
incorporation using polymerase chain reaction. All of the roots tested were found to be co-transformed with T-DNA from the
Ri-plasmid and the transgene from the binary vectors. Southern blot analysis confirmed the presence of the 35S-gfp5 gene in the plant genomes. Transgene expression was also confirmed by histochemical GUS assay and Western blot analysis for
the GFP. Attempts to induce shoot formation from the hairy roots failed. Infection of hairy roots of the soybean cyst nematode
(Heterodera glycines Ichinohe)-susceptible cultivar, Williams 82, with eggs of H. glycines race 1, resulted in the development of mature cysts about 4–5 weeks after inoculation. Thus the soybean cyst nematode could
complete its entire life cycle in transformed soybean hairy-root cultures expressing GFP. This system should be ideal for
testing genes that might impart resistance to soybean cyst nematode.
Received: 13 July 1999 / Accepted: 8 August 1999 相似文献
6.
Expression of cucumber lipid-body lipoxygenase in transgenic tobacco: lipid-body lipoxygenase is correctly targeted to seed lipid bodies 总被引:2,自引:0,他引:2
A particular isoform of lipoxygenase (LOX, EC 1.13.11.12) localized on lipid bodies has been shown by earlier investigations
to play a role during seed germination in initiating the mobilization of triacylglycerols. On lipid bodies of germinating
cucumber (Cucumis sativus L.) seedlings, the modification of linoleoyl moieties by this LOX precedes the hydrolysis of the ester bonds. We analyzed
the expression and intracellular location of this particular LOX form in leaves and seeds of tobacco (Nicotiana tabacum L.) transformed with one construct coding for cucumber lipid-body LOX and one construct coding for cucumber LOX fused with
a hemagglutinin epitope. In both tissues, the amount of lipid-body LOX was clearly detectable. Biochemical analysis revealed
that in mature seeds the foreign LOX was targeted to lipid bodies, and the preferred location of the LOX on lipid bodies was
verified by immunofluorescence microscopy. Cells of the endosperm and of the embryo exhibited fluorescence based on the immunodecoration
of LOX protein whereas very weak fluorescent label was visible in seeds of untransformed control plants. Further cytochemical
analysis of transformed plants showed that the LOX protein accumulated in the cytoplasm when green leaves lacking lipid bodies
were analyzed. Increased LOX activity was shown in young leaves of transformed plants by an increase in the amounts of endogenous
(2E)-hexenal and jasmonic acid.
Received: 9 August 1999 / Accepted: 28 September 1999 相似文献
7.
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
8.
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
9.
Hieracium is a member of the Asteraceae family, and contains sexual species in addition to apomictic species that reproduce by apospory
and produce seed without fertilization. A homologue of the floral organ-identity gene DEFICIENS (DEF) was isolated from an apomictic line of Hieracium piloselloides (Vill.) following differential display between mature ovules and those initiating autonomous embryogenesis. The gene termed
HPDEF has 93% amino acid identity with GDEF2, a DEF homologue isolated from Gerbera hybrida (D. Yu et al., 1999, Plant J. 17: 51–62), another member of the Asteraceae. In-situ analysis showed that early in floral
development HPDEF is expressed in stamen and petal primordia, indicating expected B-function activity, according to the ABC model of floral
organ identity (J. L. Bowman et al., 1991, Development 112: 1–20; E. S. Coen and E. M. Meyerowitz, 1991, Nature 353: 31–37).
However, HPDEF expression was also observed in ovule primordia and expression continued in developing ovules until anthesis, indicating
that this gene may have a role in ovule development. Expression of HPDEF was not detected in megaspore mother cells, or in sexual or aposporous embryo sacs. In sexual Hieracium, HPDEF was uniformly expressed throughout the ovule integument until anthesis. In most ovules of the apomict, however, HPDEF expression was transiently down-regulated in a specific zone in the chalazal region where cells initiating aposporous embryo
sac formation differentiate. Uniform low-level HPDEF expression was subsequently observed prior to anthesis in ovules from sexual and apomictic plants. HPDEF may be down-regulated as a consequence of apomictic initiation and/or its down-regulation may facilitate progression of apomictic
events.
Received: 15 September 1999 / Accepted: 12 October 1999 相似文献
10.
Light-induced expression of the Gsa gene encoding the heme and chlorophyll biosynthetic enzyme glutamate 1-semialdehyde aminotransferase in Chlamydomonas reinhardtii was previously shown to involve Ca2+ and calmodulin (CaM) (C. lm et al. 1996, Plant Cell 8: 2245–2253). To further analyze the signal transduction pathway for
light-induced Gsa expression, the effects of several pharmacological agents were examined. Treatment of light-dark synchronized cells with
the heterotrimeric G-protein agonist Mas-7 caused partial induction of Gsa in the dark. The phospholipase C inhibitor U73122 inhibited light induction of Gsa. Exposure of cells to light caused a sustained 3-fold increase in cellular d-inositol 1,4,5-trisphosphate (InsP3) concentration. KN-93, a specific inhibitor of Ca2+/CaM-dependent protein kinase II, inhibited light induction of Gsa. In contrast, cyclosporin A, a specific inhibitor of the Ca2+/CaM-dependent phosphoprotein phosphatase calcineurin, did not affect light induction of Gsa. These results, together with the earlier results, suggest the involvement of a canonical signal transduction pathway for
light-regulated Gsa expression that involves a heterotrimeric G-protein activation, phospholipase C-catalyzed InsP3 formation, InsP3-dependent Ca2+ release, and activation of a downstream signaling pathway through a Ca2+/CaM-dependent protein kinase.
Received: 21 October 1999 / Accepted: 3 December 1999 相似文献
11.
The temporal and spatial patterns of storage-globulin mobilization were immunohistochemically pursued in the embryonic axis
and cotyledons of vetch seed (Vicia sativa L.) during germination and early seedling growth. Embryonic axes as well as cotyledons of mature seeds contain protein bodies
with stored globulins. Prevascular strands of axes and cotyledons, the radicle and epidermal layers of axis organs were nearly
exclusively stained by vicilin antibodies whereas the cotyledonous storage mesophyll gave similar staining for vicilin and
legumin. Globulin breakdown started locally where growth and differentiation commenced in the axis. There, vicilin mobilization
preceded legumin mobilization. Thus vicilin represents the initial source of amino acids for early growth and differentiation
processes in vetch. Legumin presumably only serves as a bulk amino acid source for subsequent seedling growth during postgerminative
globulin degradation. During the first 2–3 d after the start of imbibition the axis was depleted of globulins whereas no decrease
in immunostainability was detected in the cotyledons except in their vascular strands where immunostainability was almost
completely lost at this time. Continuous vascular strands were established at the third day when globulin breakdown was finished
in the axis but had just started in the cotyledon mesophyll. Protein mobilization proceeded in a small zone from the epidermis
towards the vascular strands in the center of the cotyledons. In this zone the storage cells, which initially appeared densely
packed with starch grains and protein bodies, concomitantly transformed into cells with a large central vacuole and only a
thin cytoplasmic layer attached to the cell wall. These results agree well with the hypothesis that during the first 2 d after
imbibition the axis is autonomous in amino acid provision. After the endogenous reserves of the axis are depleted and the
conductive tissue has differentiated, globulins are mobilized in the cotyledons, suggesting that then the amino acid supply
is taken over by the cotyledons. For comparison with other degradation patterns we used garden bean (Phaseolus vulgaris L) and rape (Brassica napus L.) as reference plants.
Received: 3 August 1999 / Accepted: 11 December 1999 相似文献
12.
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
13.
The hypersensitive response is associated with host and nonhost resistance to Phytophthora infestans
The interaction between Phytophthora infestans (Mont.) de Bary and Solanum was examined cytologically using a diverse set of wild Solanum species and potato (S. tuberosum L.) cultivars with various levels of resistance to late blight. In wild Solanum species, in potato cultivars carrying known resistance (R) genes and in nonhosts the major defense reaction appeared to be the hypersensitive response (HR). In fully resistant Solanum species and nonhosts, the HR was fast and occurred within 22 h. This resulted in the death of one to three cells. In partially
resistant clones, the HR was induced between 16 and 46 h, and resulted in HR lesions consisting of five or more dead cells,
from which hyphae were occasionally able to escape to establish a biotrophic interaction. These results demonstrate the quantitative
nature of the resistance to P. infestans. The effectiveness of the HR in restricting growth of the pathogen differed considerably between clones and correlated with
resistance levels. Other responses associated with the defense reaction were deposition of callose and extracellular globules
containing phenolic compounds. These globules were deposited near cells showing the HR, and may function in cell wall strengthening.
Received: 22 April 1999 / Accepted: 4 November 1999 相似文献
14.
Inorganic carbon (Ci) uptake and efflux has been investigated in the marine microalga Nannochloropsis gaditana Lubian by monitoring CO2 fluxes in cell suspensions using mass spectrometry. Addition of H13CO3
− to cell suspensions in the dark caused a transient increase in the CO2 concentration in the medium far in excess of the equilibrium CO2 concentration. The magnitude of this release was dependent on the length of time the cells had been kept in the dark. Once
equilibrium between the Ci species had been achieved, a CO2 efflux was observed after saturating light intensity was applied to the cells. External carbonic anhydrase (CA) was not detected
nor does this species demonstrate a capacity to take up CO2 by active transport. Photosynthetic O2 evolution and the release CO2 in the dark depend on HCO3
− uptake since both were inhibited by the anion exchange inhibitor, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS).
The bicarbonate uptake mechanism requires light but can also continue for short periods in the dark. Ethoxyzolamide, a CA
inhibitor, markedly inhibited CO2 efflux in the dark, indicating that CO2 efflux was dependent upon the intracellular dehydration of HCO3
−. These results indicate that Nannochloropsis possesses a bicarbonate uptake system which causes the accumulation of high intracellular Ci levels and an internal CA which
maintains the equilibrium between CO2 and HCO3
− and thus causes a subsequent release of CO2 to the external medium.
Received: 20 September 1999 / Accepted: 25 October 1999 相似文献
15.
Microtubule nucleation in interphase plant cells primarily occurs through branching from pre-existing microtubules at dispersed sites in the cell cortex. The minus ends of new microtubules are often released from the sites of nucleation, and the free microtubules are then transported to new locations by polymer treadmilling. These nucleation-and-release events are characteristic features of plant arrays in interphase cells, but little is known about the spatiotemporal control of these events by nucleating protein complexes. We visualized the dynamics of two fluorescently-tagged γ-tubulin complex proteins, GCP2 and GCP3, in Arabidopsis thaliana. These probes labelled motile complexes in the cytosol that transiently stabilized at fixed locations in the cell cortex. Recruitment of labelled complexes occurred preferentially along existing cortical microtubules, from which new microtubule was synthesized in a branching manner, or in parallel to the existing microtubule. Complexes localized to microtubules were approximately 10-fold more likely to display nucleation than were complexes recruited to other locations. Nucleating complexes remained stable until daughter microtubules were either completely depolymerized from their plus ends or released by katanin-dependent severing activity. These observations suggest that the nucleation complexes are primarily activated on association with microtubule lattices, and that nucleation complex stability depends on association with daughter microtubules and is regulated in part by katanin activity. 相似文献
16.
The alga Chlamydomonas reinhardtii contains cytoplasmic vacuoles that are often filled with a dense granule that is released from the cell by exocytosis. Purified
granules contained polyphosphate, complexed with calcium and magnesium, as the predominant inorganic components. Antiserum
was raised against the major 70-kDa protein in granules purified from wall-deficient (cw15) mutants, which reacted on immunoblots with larger glycoprotein complexes in purified cell wall fractions from wild-type
cells. Confocal fluorescence microscopy detected binding of these antibodies predominantly at the periphery of wall-containing
C. reinhardtiiy1 cells but primarily to loci in the interior of cells of the cw15 strain. Immunoelectron microscopy demonstrated that the 70-kDa protein was localized in vacuolar granules and the trans-Golgi network in sections of cw15 cells but not in the cytosol or chloroplast. Treatment of cells with a dye, fluorescent in its protonated form, indicated
that the pH within vacuoles was lower than that in the cytosol, which suggested that the vacuoles are similar to lysosomes.
Thus, the vacuoles may serve a dual function to provide an environment for degradation within the cell and also serve as a
vehicle for secretion of specific proteins.
Received: 29 September 1999 / Accepted: 20 November 1999 相似文献
17.
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
18.
Egg cells were analysed cytologically during the female receptivity period in maize (Zea mays L., line A 188). Three classes of egg cell were distinguished: type A – small, non-vacuolated cells with a central nucleus;
type B – larger cells with small vacuoles surrounding the perinuclear cytoplasm located in the middle of the cell; type C
– big cells with a large apical vacuole and the mid-basal perinuclear cytoplasm. The less-dense cytoplasm of the vacuolated
egg cells usually contained numerous cup- or bell-shaped mitochondria. The three egg types appear to correspond to three late
stages of egg cell differentiation. The frequencies of each of the three egg types were monitored in developing maize ears
before and after pollination. In young ears, with the silks just extending out of the husks, small A-type cells were found
in about 86% of ovules. Their frequency decreased to about 58% at the optimum silk length, remained unchanged in non-pollinated
ears, and fell to 16% at the end of the female receptivity period. However, after pollination and before fertilisation the
frequency of these cells decreased to about 33%, and the larger vacuolated egg cells (types B and C) prevailed. At various
stages of the receptivity period, pollination accelerated changes in the egg population, increasing the number of ovules bearing
larger, vacuolated egg cells. Experiments with silk removal demonstrated that putative pollination signals act immediately
after pollen deposition and are not species-specific.
Received: 5 February 1999 / Accepted: 28 August 1999 相似文献
19.
Expansion of transgenic tobacco protoplasts expressing pumpkin ascorbate oxidase is more rapid than that of wild-type protoplasts 总被引:10,自引:0,他引:10
When pumpkin (Cucurbita spp., cv. Ebisu Nankin) ascorbate oxidase cDNA was introduced into cultured cells of tobacco BY-2 (Nicotiana tabacum L. cv. Bright Yellow No. 2) by Agrobacterium-mediated transformation, the transgenic cells expressed and secreted the recombinant pumpkin ascorbate oxidase into the culture
medium. These transgenic cells showed no morphological difference from wild-type cells. However, in the presence of applied
hormones protoplasts prepared from the transgenic cells elongated more rapidly than those of wild-type cells. We propose that
ascorbate oxidase may play a key role in the regulation of cell expansion perhaps by controlling transport processes through
the plasma membrane, but not by affecting the cell wall.
Received: 28 October 1999 / Accepted: 18 January 2000 相似文献
20.
A microsomal preparation from suspension-cultured potato stem cells (Solanum tuberosum L. cv. AZY) was incubated with [14C]acetyl-CoA resulting in a precipitable radiolabeled product. Analysis of the product revealed that it consisted mostly of
acetylated proteins and cell wall polysaccharides, including xyloglucan, homogalacturonan and rhamnogalacturonan I. Thus,
acetyl-CoA is a donor-substrate for the O-acetylation of wall polysaccharides. A rhamnogalacturonan acetylesterase was used to develop an assay to measure and characterize
rhamnogalacturonan O-acetyl transferase activity in the microsomal preparation. Using this assay, it was shown that the transferase activity was
highest during the linear growth phase of the cells, had a pH-optimum at pH 7.0, a temperature optimum at 30 °C, an apparent
K
m of 35 μM and an apparent V
max of 0.9 pkat per mg protein. Further analysis of the radiolabeled acetylated product revealed that it had a molecular mass
>500 kDa.
Received: 3 July 1999; Accepted: 27 September 1999 相似文献