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1.
A cytoskeletal basis for wood formation in angiosperm trees: the involvement of cortical microtubules 总被引:3,自引:0,他引:3
Rearrangements of cortical microtubules (CMTs) during the differentiation of axial secondary xylem elements within taproots
and shoots of Aesculus hippocastanum L. (horse-chestnut) are described. A correlative approach was employed using indirect immunofluorescence microscopy of α-tubulin
in 6- to 10-μm sections and transmission electron microscopy of ultrathin sections. All cell types – fibres, vessel elements
and axial parenchyma – derive from fusiform cambial cells which contain randomly oriented CMTs. At the early stages of development,
fibres and axial parenchyma cells possess helically arranged CMTs, which increase in number as secondary wall thickening proceeds
and simple pits develop. In contrast, incipient vessel elements are distinguished by the marking out of sites of bordered
pits; these sites first appear as microtubule-free regions within the reticulum of randomly oriented CMTs that characterises
their precursor fusiform cambial cells. Subsequently, the ring of CMTs which develops at the periphery of the microtubule-free
region decreases in diameter as the over-arching pit border is formed. Like bordered pits, large-diameter, non-bordered pits
(contact pits) which develop between vessel elements and adjacent contact ray cells originate as microtubule-free regions
and are also associated with development of a ring of CMTs at the periphery. In the case of contact pits, however, there is
no reduction in the diameter of the CMT ring during pit development. Tertiary cell wall thickenings are also a feature of
vessel elements and appear to form at sites where bands of laterally associated, transversely oriented CMTs, separated from
each other by microtubule-free zones, are found. Later, these bands of CMTs become narrower, and separate into pairs of microtubule
bundles located on each side of the developing wall thickening. Development of perforations between vessel elements is also
associated with the presence of a ring of CMTs at their periphery.
Received: 13 July 1998 / Accepted: 30 November 1998 相似文献
2.
Effects of temperature and precipitation on xylem cell production by the cambium, radial cell expansion and secondary wall
thickening in larch stems have been studied. The observations were carried out over two seasons on ten 50- to 60-year-old
trees, growing in central Siberia and chosen according to growth rate (the number of cells in radial rows of each of two of
the preceding seasons was equal). The data on the number of cells in differentiation zones and mature xylem along radial rows
of tracheids, radial and tangential sizes of tracheids and their lumina were used for calculating cambial activity, the rates
and durations of cell development in the zones, and both the thickness and cross-sectional areas of tracheid walls. The mean
day air temperature, mean maximum diurnal and mean minimum nocturnal temperatures as well as precipitation have been shown
by correlation and regression analyses to affect differentially separate stages of tracheid differentiation. Throughout all
the seasons it was temperature that had the main influence on the initial divisions in the xylem, radial cell expansion and
biomass accumulation. However, the levels of such an effect on separate stages of cytogenesis were different, especially the
influence of nocturnal temperature on xylem cell production by cambium and primary wall growth. The optimum values of temperature
and precipitation for cell production by cambium, for radial cell expansion and secondary wall thickening have been calculated.
These optimum values of the first and second processes proved to be practically equal, while the last differs considerably
in response to temperature. The data are discussed in connection with formation of early and late tracheids.
Received: 3 July 1996 / Accepted: 7 February 1997 相似文献
3.
Wood formation in poplar: identification, characterization, and seasonal variation of xylem proteins 总被引:9,自引:0,他引:9
Proteins that are preferentially produced in developing xylem may play a substantial role in xylogenesis. To reveal the identity
of these proteins, comparative two-dimensional polyacrylamide gel electrophoresis was performed on young differentiating xylem,
mature xylem, and bark of poplar (Populus trichocarpa Hook. cv. `Trichobel') harvested at different times of the year. The most-abundant xylem proteins were identified by microsequence
analysis. For 17 of these proteins a putative function could be assigned based on similarity with previously characterized
proteins, and for 15 out of these corresponding expressed sequence tags (ESTs) were found in the poplar EST database. The
identified xylem–preferential proteins, defined by comparing the protein patterns from xylem and bark, were all involved in
the phenylpropanoid pathway: two caffeoyl-coenzyme A O-methyltransferases (CCoAOMT), one phenylcoumaran benzylic ether reductase (PCBER), one bispecific caffeic acid/5-hydroxyferulic
acid O-methyltransferase (COMT), five S-adenosyl-L-methionine synthetases, and one homologue of glycine hydroxymethyltransferase (GHMT). Remarkably, the biological function
of the two most-abundant xylem-preferential proteins (PCBER and a GHMT homologue) remains unclear. In addition, several housekeeping
enzymes were identified: two enolases, two glutamine synthetases, one 70-kDa heat-shock cognate, one calreticulin, and one
α-tubulin. In comparison to the xylem-preferential proteins, the housekeeping proteins were expressed at significant levels
in the bark as well. Also, several additional protein spots were detected for CCoAOMT, PCBER, and COMT by immunoblot. Our
data show that for the study of xylogenesis, two-dimensional protein gel comparisons combined with systematic protein sequencing
may yield information complementary to that from EST sequencing strategies.
Received: 28 June 1999 / Accepted: 3 September 1999 相似文献
4.
Summary. Advanced glycation end products (AGEs) and advanced lipoxidation end products (ALEs) are implicated in many age-related chronic
diseases and in protein aging. Recent studies suggest that pyridoxamine (PM) is an efficient AGEs/ALEs inhibitor in various
biological systems. Because malondialdehyde (MDA) is an important intermediate in the formation of ALEs during lipid peroxidation,
the purpose of this study is to determine whether PM can trap MDA directly and thereby prevent ALEs formation. PM reacted
readily with MDA under physiological conditions. Within 6 h, a 1-pyridoxamino-propenal adduct derived from reaction of equimolar
PM + MDA was detected. A 1-amino-3-iminopropene complex and a dihydropyridine-pyridinium complex were also identified after
7 d incubation. PM also greatly inhibited the lipofuscin-like fluorescence formation induced by MDA reaction with bovine serum
albumin (BSA). Our results showed clearly that PM inhibited the formation of ALEs by trapping MDA directly under physiological
condition, and provide insight into the mechanism of action of PM in protecting proteins against carbonyl stress. 相似文献
5.
6.
Summary A correlative study, using indirect immunofluorescence microscopy (IIF) of anti--tubulin stained sections and transmission electron microscopy (TEM), gave details of the involvement of cortical microtubules (CMTs) in the development of bordered pits in secondary xylem vessel elements ofAesculus hippocastanum L. In addition, aspects of wall cytochemistry were studied during this process using the Thiéry (PATAg) test, immunolocalization with the monoclonal antibodies JIM5 and JIM7, and a range of other cytochemical procedures. IIF showed that the alternately-arranged pits are pre-figured as perforations within a reticulum of randomly-oriented CMTs before any secondary wall thickening is obvious. Each incipient pit border is subsequently delimited by a circle of CMTs whose diameter decreases as deposition of secondary wall takes place around the perforation. These IIF observations are corroborated by a parallel TEM study. During the period of bordered pit formation, the secondary walls of the cell are lignifying. At maturity, however, the pit membrane is unlignified and continues to stain strongly with the monoclonal antibody JIM5, a marker of primary, juvenile wall. The results are discussed in terms of the relationship of the CMT cytoskeleton with development of bordered pits.Abbrevations BSA
bovine serum albumin
- CMT(s)
cortical micro-tubule(s)
- EGTA
ethylene glycol-bis-(ß-aminoethyl ether)-N,N,N,N-tetraacetic acid
- FITC
fluorescein isothiocyanate
- IIP
indirect immunofluorescence
- MAP
microtubule-associated protein
- mf(s)
wall microfibril(s)
- MTSB
microtubule-stabilising buffer
- PATAg
periodic acid-thiocarbohydrazide-silver proteinate
- PBS
Phosphate-buffered saline
- PIPES
piperazine-N,N-bis-[2-ethylsulphonic acid]
- SVS
secondary vascular system
- TEM
transmission electron microscopy 相似文献
7.
Chemical-induced apoptotic cell death in tomato cells: involvement of caspase-like proteases 总被引:16,自引:0,他引:16
A new system to study programmed cell death in plants is described. Tomato (Lycopersicon esculentum Mill.) suspension cells were induced to undergo programmed cell death by treatment with known inducers of apoptosis in mammalian
cells. This chemical-induced cell death was accompanied by the characteristic features of apoptosis in animal cells, such
as typical changes in nuclear morphology, the fragmentation of the nucleus and DNA fragmentation. In search of processes involved
in plant apoptotic cell death, specific enzyme inhibitors were tested for cell-death-inhibiting activity. Our results showed
that proteolysis plays a crucial role in apoptosis in plants. Furthermore, caspase-specific peptide inhibitors were found
to be potent inhibitors of the chemical-induced cell death in tomato cells, indicating that, as in animal systems, caspase-like
proteases are involved in the apoptotic cell death pathway in plants.
Received: 5 August 1999 / Accepted: 14 March 2000 相似文献
8.
Maize (Zea mays L.) cell cultures incorporated radioactivity from [14C]cinnamate into hydroxycinnamoyl-CoA derivatives and then into polysaccharide-bound feruloyl residues. Within 5–20 min, the
CoA pool had lost its 14C by turnover and little or no further incorporation into polysaccharides then occurred. The system was thus effectively a
pulse–chase experiment. Kinetics of radiolabelling of diferulates (also known as dehydrodiferulates) varied with culture age.
In young (1–3 d) cultures, polysaccharide-bound [14C]feruloyl- and [14C]diferuloyl residues were both detectable within 1 min of [14C]cinnamate feeding. Thus, feruloyl residues were dimerised <1 min after their attachment to polysaccharides. For at least
the first 2.3 h after [14C]cinnamate feeding, polysaccharide-bound [14C]diferuloyl residues remained almost constant at ≈7% of the total polysaccharide-bound [14C]ferulate derivatives. Since feruloyl residues are attached to polysaccharides <1 min after the biosynthesis of the latter,
and >10 min before secretion, the data show that extensive feruloyl coupling occurred intra-protoplasmically. Exogenous H2O2 (1 mM) caused little additional feruloyl coupling; therefore, wall-localised coupling may have been peroxidase-limited. In
older (e.g. 4 d) cultures, less intraprotoplasmic coupling occurred: during the first 2.5 h, polysaccharide-bound [14C]diferuloyl residues were a steady 1.4% of the total polysaccharide-bound [14C]ferulate derivatives. In contrast to the situation in younger cultures, exogenous H2O2 induced a rapid 4- to 6-fold increase in all coupling products, indicating that coupling in the walls was H2O2-limited. In both 2- and 4-d-old cultures, polysaccharide-bound 14C-trimers and larger coupling products exceeded [14C]diferulates 3- to 4-fold, but followed similar kinetics. Thus, although all known dimers of ferulate can now be individually
quantified, it appears to be trimers and larger products that make the major contribution to cross-linking of wall polysaccharides
in cultured maize cells. We argue that feruloyl arabinoxylans that are cross-linked before and after secretion are likely
to loosen and tighten the cell wall, respectively. The consequences for the control of cell expansion and for the response
of cell walls to an oxidative burst are discussed.
Received: 19 January 2000 / Accepted: 13 April 2000 相似文献
9.
Summary. Our aim was to develop a liquid chromatography and electrospray ionization tandem mass spectrometry (LCMS2) method to measure free amino acid (FAA) and dipeptide (DP) concentrations in biological fluids. We synthesized chloroformate
derivatives of FAA and DP, identified the major precursor ions and used LCMS2 to obtain the most intense product ions. Using serial dilutions of unlabeled and labeled standards ([2H3]-L-Dopa, homoarginine, homophenylalanine, [15N]-Glutamine and [2H3]-methionine), we observed linear relationships in MS response that we used to calculate the amounts of FAA and DP in biological
samples. This method is sensitive with a limit of detection (LOD) for most of the FAAs and DPs tested in the 0.05–1 pmol range
and is linear over 3–5 orders of magnitude when many metabolites were measured simultaneously. Reproducibility and between
run or daily variations were <10% for most FAAs and DPs. We applied this method to human samples and quantitatively measured
21 FAAs and 2 DPs in 200 μl CSF, 31 FAAs and 6 DPs in 100 μl plasma, and 23 FAAs and 5 DPs in 200 μl urine. These data demonstrate
the potential for using LCMS2 to discover changes in FAA and DP metabolic pathways that occur during disease pathogenesis. 相似文献
10.
11.
Mechanisms of primordium formation during adventitious root development from walnut cotyledon explants 总被引:7,自引:0,他引:7
In walnut (Juglans regia L.), an otherwise difficult-to-root species, explants of cotyledons have been shown to generate complete roots in the absence
of exogenous growth regulators. In the present study, this process of root formation was shown to follow a pattern of adventitious,
rather than primary or lateral, ontogeny: (i) the arrangement of vascular bundles in the region of root formation was of the
petiole type; (ii) a typical root primordium was formed at the side of the procambium within a meristematic ring of actively
dividing cells located around each vascular bundle; (iii) the developing root apical meristem was connected in a lateral way
with the vascular bundle of the petiole. This adventitious root formation occurred in three main stages of cell division,
primordium formation and organization of apical meristem. These stages were characterized by expression of LATERAL ROOT PRIMORDIUM-1 and CHALCONE SYNTHASE genes, which were found to be sequentially expressed during the formation of the primordium. Activation of genes related
to root cell differentiation started at the early stage of primordium formation prior to organization of the root apical meristem.
The systematic development of adventitious root primordia at a precise site gave indications on the positional and biochemical
cues that are necessary for adventitious root formation.
Received: 30 July 1999 / Accepted: 16 February 2000 相似文献
12.
Inhibitors of the carrier-mediated influx of auxin in suspension-cultured tobacco cells 总被引:6,自引:0,他引:6
Active auxin transport in plant cells is catalyzed by two carriers working in opposite directions at the plasma membrane,
the influx and efflux carriers. A role for the efflux carrier in polar auxin transport (PAT) in plants has been shown from
studies using phytotropins. Phytotropins have been invaluable in demonstrating that PAT is essential to ensure polarized and
coordinated growth and to provide plants with the capacity to respond to environmental stimuli. However, the function of the
influx carrier at the whole-plant level is unknown. Our work aims to identify new auxin-transport inhibitors which could be
employed to investigate its function. Thirty-five aryl and aryloxyalkylcarboxylic acids were assayed for their ability to
perturb the accumulation of 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthalene-1-acetic acid (1-NAA) in suspension-cultured
tobacco (Nicotiana tabacum L.) cells. As 2,4-D and 1-NAA are preferentially transported by the influx and efflux carriers, respectively, accumulation
experiments utilizing synthetic auxins provide independant information on the activities of both carriers. The majority (60%)
of compounds half-inhibited the carrier-mediated influx of [14C]2,4-D at concentrations of less than 10 μM. Most failed to interfere with [3H]NAA efflux, at least in the short term. Even though they increasingly perturbed auxin efflux when given a prolonged treatment,
several compounds were much better at discriminating between influx and efflux carrier activities than naphthalene-2-acetic
acid which is commonly employed to investigate influx-carrier properties. Structure-activity relationships and factors influencing
ligand specificity with regard to auxin carriers are discussed.
Received: 28 June 1999 / Accepted: 28 August 1999 相似文献
13.
Vander Mijnsbrugge K Beeckman H De Rycke R Van Montagu M Engler G Boerjan W 《Planta》2000,211(4):502-509
It has previously been shown (D.R. Gang et al., 1999, J Biol Chem 274: 7516–7527) that the most abundant protein in the secondary
xylem of poplar (Populus trichocarpa cv. `Trichobel') is a phenylcoumaran benzylic ether reductase (PCBER), an enzyme involved in lignan synthesis. Here, the
distribution and abundance of PCBER in poplar was studied at both the RNA and protein level. The cellular expression pattern
was determined by immunolocalization of greenhouse-grown plants as well as of a field-grown poplar. Compared to other poplar
tissues, PCBER is preferentially produced in the secondary xylem of stems and roots and is associated with the active growth
period. The protein is present in all cells of the young differentiating xylem, corresponding to the zone of active phenylpropanoid
metabolism and lignification. In addition, PCBER is located in young differentiating phloem fibers, in xylem ray parenchyma,
and in xylem parenchyma cells at the growth-ring border. Essentially the same expression pattern was observed in poplars grown
in greenhouses and in the field. The synthesis of PCBER in phenylpropanoid-synthesizing tissues was confirmed in a bending
experiment. Induction of PCBER was observed in the pith of mechanically bent poplar stems, where phenylpropanoid metabolism
is induced. These results indicate that the products of PCBER activity are synthesized mainly in lignifying tissues, suggesting
a role in wood development.
Received: 28 September 1999 / Accepted: 15 March 2000 相似文献
14.
A nonphotochemical-quenching-deficient mutant of Arabidopsis thaliana possessing normal pigment composition and xanthophyll-cycle activity 总被引:1,自引:0,他引:1
Higher-plant chloroplasts alter the distribution of absorbed radiant energy between photosynthesis and heat formation in
response to changing illumination level or environmental stress. Fluorescence imaging was used to screen 62 yellow-green T-DNA
insertion mutant lines of Arabidopsis thaliana (L.) Heynh. for reduced photoprotective nonphotochemical quenching (NPQ) capacity. Pulse-modulation fluorometry was employed
to characterize one line (denoted Lsr1−) that exhibited an approximately 50% reduction in NPQ compared to the wild type (WT). The loss in NPQ capacity was associated
with the ΔpH-dependent phase of quenching (qE). Under the growth conditions employed, pigment composition and levels of the
six photosystem-II light-harvesting chlorophyll a/b proteins were identical in mutant and WT. Changes in the in-vivo levels of the xanthophyll pigments violaxanthin, antheraxanthin,
and zeaxanthin in excess light were the same for mutant and WT. However, use of the violaxanthin de-epoxidase inhibitor dithiothreitol
indicated that a zeaxanthin-dependent component of NPQ was specifically reduced in the mutant. The mutant exhibited diminished
suppression of minimum fluorescence yield (F
o
) in intense light suggesting an altered threshold in the mechanism of response to light stress in the mutant. The NPQ-deficient
phenotype was meiotically transmissible as a semidominant trait and mapped near marker T27K12 on chromosome 1. The results
suggest that the mutant is defective in sensing the transthylakoid ΔpH that reports exposure to excessive illumination.
Received: 26 May 1999 / Accepted: 17 June 1999 相似文献
15.
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
16.
We have developed a new strategy designated SIMF (Systematic Insertional Mutagenesis of Families), to identify DNA insertions
in many members of a gene family simultaneously. This method requires only a short amino acid sequence conserved in all members
of the family to make a degenerate oligonucleotide, and a sequence from the end of the DNA insertion. The SIMF strategy was
successfully applied to the large maize R2R3 Myb family of regulatory genes, and Mutator insertions in several novel Myb genes were identified. Application of this technique to identify insertions in other large gene families could significantly
decrease the effort involved in screening at the same time for insertions in all members of groups of genes that share a limited
sequence identity.
Received: 1 June 2000 / Accepted: 26 June 2000 相似文献
17.
18.
Cucumber (Cucumis sativus L.) seedlings grown in microgravity developed a peg on each side of the transition zone between hypocotyl and root, whereas
seedlings grown in a horizontal position on the ground developed a peg on the concave side of the gravitropically bending
transition zone. The morphological features of the space-grown seedlings were similar to those of seedlings grown in a vertical
position on the ground with their radicles pointing down: both became two-pegged seedlings. Morphogenesis of cucumber seedlings
is thus inhibited by gravity. Analysis by in-situ hybridization of an auxin-inducible gene, CS-IAA1, showed that its mRNA accumulated to a much greater extent on the lower side of the transition zone in the horizontally placed
seedlings on the ground just prior to and during the initiation period of peg formation. On the other hand, when seedlings
were grown in microgravity or in a vertical position on the ground, accumulation of CS-IAA1 mRNA occurred all around the transition zone. Accumulation of CS-IAA1 mRNA in horizontally grown seedlings appreciably decreased on the upper side of the transition zone and increased on the
lower side upon gravistimulation, compared with the two-pegged seedlings. Application of IAA to seedlings in a horizontal
position caused the development of a peg on each side of the transition zone, or a collar-like protuberance, depending on
the concentration used. These results suggest that upon gravistimulation the auxin concentration on the upper side of the
horizontally placed transition zone is reduced to a level below the threshold value necessary for peg formation. Space-grown
seedlings of cucumber might develop two pegs symmetrically because the auxin level in the entire transition zone is maintained
above the threshold. This spaceflight experiment verified for the first time that auxin does not redistribute in microgravity.
Received: 10 February 2000 / Accepted: 15 March 2000 相似文献
19.
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
20.
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