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1.
Most members of the genus Hieracium are apomictic and set seed without fertilization, but sexual forms also exist. A cytological study was conducted on an apomictic
accession of H. aurantiacum (A3.4) and also H. piloselloides (D3) to precisely define the cellular basis for apomixis. The apomictic events were compared with the sexual events in a
self-incompatible isolate of H. pilosella (P4). All plants were maintained as vegetatively propagated lines each derived from a single plant. Sexual P4 exhibited characteristic
events of polygonum-type embryo sac formation, showed no latent apomitic tendencies, and depended upon fertilization to set
seed. In contrast, D3 and A3.4 were autonomous aposporous apomicts, forming both embryo and endosperm spontaneously inside
an unreduced embryo sac. The two apomicts exhibited distinct mechanisms, but variation was also observed within each apomictic
line. Seeds from apomicts often contained more than one embryo. A degree of developmental instability was also observed amongst
germinated seedlings and included variation in meristem and cotyledon number, altered phyllotaxis, callus formation, and seedling
fusion. In most cases abnormal seedlings developed into normal plants. Such phenomena were not observed following germination
of hybrid seeds derived from crosses between sexual P4 and the apomictic plants. The three plants can now be used in inheritance
studies and also to investigate the molecular mechanisms controlling apomixis.
Received: 11 February 1998 / Revision accepted: 23 July 1998 相似文献
2.
R. A. Bicknell 《Sexual plant reproduction》1997,10(3):168-172
As in most taxa that contain gametophytic apomicts, all of the apomictic biotypes studied so far in the genus Hieracium subgenus Pilosella have been recorded as polyploids. As part of a study of variation in apomictically derived populations of H. aurantiacum, a diploid plant was identified. Apospory, the mechanism of apomixis typically observed in this taxon, was observed in this
plant. Unreduced megagametophytes at various developmental stages were commonly observed in the developing ovules, and endosperm
formation was autonomous. The eventual seed set, however, was low. This appears to have been due to the proliferation of competing
megagametophytes and embryos within each ovule. Pollen sterility was also observed, primarily resulting from the dysfunction
of microgametogenesis at the uninucleate stage.
Received: 3 September 1996 / Revision accepted: 21 March 1997 相似文献
3.
Callose accumulates in the walls of cells undergoing megasporogenesis during embryo sac formation in angiosperm ovules. Deficiencies
in callose deposition have been observed in apomictic plants and causal linkages between altered callose deposition and apomictic
initiation proposed. In apomictic Hieracium, embryo sacs initiate by sexual and apomictic processes within an ovule, but sexual development terminates in successful
apomicts. Callose deposition and the events that lead to sexual termination were examined in different Hieracium apomicts that form initials pre- and post-meiosis. In apomictic plants, callose was not detected in initial cell walls and
deficiencies in callose deposition were not observed in cells undergoing megasporogenesis. Multiple initial formation pre-meiosis
resulted in physical distortion of cells undergoing megasporogenesis, persistence of callose and termination of the sexual
pathway. In apomictic plants, callose persistence did not correlate with altered spatial or temporal expression of a β-1,3-glucanase
gene (HpGluc) encoding a putative callose-degrading enzyme. Expression analysis indicated HpGluc might function during ovule growth and embryo sac expansion in addition to callose dissolution in sexual and apomictic plants.
Initial formation pre-meiosis might therefore limit the access of HpGluc protein to callose substrate while the expansion of aposporous embryo sacs is promoted. Callose deposition and dissolution
during megasporogenesis were unaffected when initials formed post-meiosis, indicating other events cause sexual termination.
Apomixis in Hieracium is not caused by changes in callose distribution but by events that lead to initial cell formation. The timing of initial
formation can in turn influence callose dissolution.
Received: 18 April 2000 / Accepted: 10 July 2000 相似文献
4.
Apomixis is facultative in characterized members of the genus Hieracium. The three components that comprise the apomictic mechanism include apospory followed by autonomous embryo and endosperm
formation. The time of aposporous embryo sac initiation and mode of embryo sac formation are different in Hieracium piloselloides (D3) and Hieracium aurantiacum (A3.4). Genetic studies have shown that a single dominant locus encodes all three components of apomixis in both species
(Bicknell et al. 2000). We histologically examined a range of related, genetically characterized apomictic Hieracium plants derived from D3 and A3.4 to assess conservation of the apomictic mechanism in different genetic backgrounds. The plants
varied in ploidy, and also in the amount of DNA introduced from sexual Hieracium pilosella (P4). An apomictic hybrid from a cross between the two apomicts was also examined. The developmental processes observed in
the parental apomicts were not conserved in the examined plants and alterations occurred in the components of apomixis. One
plant also exhibited adventitious embryony. The results show that other genetic factors can modify apomixis with respect to
time of initiation, spatial location, and mode of developmental progression. Both the apomictic locus and the modifiers are
essential for efficient penetrance of the trait in Hieracium. Some of the findings in Hieracium correspond with observations in Ranunculus and this is discussed in terms of models for apomictic development and the control of apomixis in crops.
Received: 21 June 1999 / Revision accepted: 17 November 1999 相似文献
5.
A group of frequent cDNA clones from a young-leaf cDNA library was found to code for a homologue of S-ribonucleases (S-RNases)
involved in gametophytic incompatibility and the so-called S-like RNases active in flowers and in vegetative tissues. The
derived amino acid sequence starts with a signal peptide and has a 27-amino-acid C-terminal extension of unknown function.
The barley (Hordeum vulgare L.) gene, rsh1 (for RNase S-like homologue) corresponding to the cDNA clones was isolated. The gene has three introns and the position of
one intron corresponds to the site of the single, small intron in the S-RNase genes. The deduced amino acid sequence of mature
RSH1 shares 35% identical and 58% similar amino acid residues with an S-like RNase from tomato, RNase LE. However, two active-site
histidine residues, conserved between all S and S-like RNases are replaced by serine residues in RSH1. The new barley RNase
S-like homologue is clearly related to the family of active RNases but is probably not active as an RNase. Sequences from
the same class of presumably inactive RNases have been recorded in maize, rice and sorghum. The barley gene is exclusively
expressed in young leaf tissue and is substantially induced by light.
Received: 26 July 1999 / Accepted: 26 October 1999 相似文献
6.
Takahashi H Kamada M Yamazaki Y Fujii N Higashitani A Aizawa S Yoshizaki I Kamigaichi S Mukai C Shimazu T Fukui K 《Planta》2000,210(3):515-518
Seedlings of most cucurbitaceous plants develop a peg (protuberance caused by cell outgrowth) on the transition zone between
the hypocotyl and root. The peg is necessary for removing the seed coat after germination. In our spaceflight experiments
on the STS-95 space shuttle, Discovery, we found that cucumber (Cucumis sativus L.) seedlings grown under microgravity conditions developed two pegs symmetrically at the transition zone. Thus, cucumber
seedlings potentially develop two pegs and do not require gravity for peg formation itself, but on the ground the development
of one peg is suppressed in response to gravity. This may be considered as negative control of morphogenesis by gravity.
Received: 17 August 1999 / Accepted: 4 October 1999 相似文献
7.
8.
To discover highly apomictic and amphimictic Allium tuberosum diploids, we evaluated the degree of apomixis in three dihaploids (2n=16, 2x), KaD2, TeD1 and GMD1, derived from highly apomictic
tetraploids. The degree of apomixis, calculated as the percentage of diploid seedlings in the progeny obtained after cross-pollination
with tetraploid cultivars, was 96% in KaD2, 7% in TeD1 and 39% in GMD1. In addition to this general index of apomictic nature,
two analytical indices were evaluated in KaD2 and TeD1. The degree of diplospory, calculated as the percentage of endoreduplicated
embryo-sac mother cells, was 96% in KaD2 and 2% in TeD1. The degree of parthenogenesis, calculated as the percentage of ovules
with the egg cell developing parthenogenetically, was 98% in KaD2 and 10% in TeD1. Among angiosperms with gametophytic apomixis,
KaD2 is the first diploid apomict whose reproductive mode has been fully described by these three quantitative indices of
apomictic nature. And TeD1 is the first highly amphimictic plant found in the A. tuberosum complex. Although TeD1 is poorly fertile, the present results encourage further screening trials for highly fertile, highly
amphimictic dihaploids, which may be effective counterparts to KaD2 in diploid-level cross experiments to genetically analyze
apomixis in A. tuberosum.
Received: 4 December 1995 / Revision accepted: 8 May 1996 相似文献
9.
D. Grimanelli Martha Hernández Enrico Perotti Yves Savidan 《Sexual plant reproduction》1997,10(5):279-282
Imprinting in the endosperm of angiosperms, a phenomena by which expression of alleles differs depending on whether they
originate from the male or female parent, has been shown to explain most failure of interploidy or interspecific crosses in
plants. Because of imprinting, seeds develop normally only if a specific dosage is represented in the endosperm, with the
relative contributions of genomes in the ratio of two maternal doses to one paternal dose (2m:1p). In Tripsacum, a wild relative of maize, all polyploids reproduce through the diplosporous type of apomixis. Diplospory results from meiotic
failure in megasporocytes that develop into eight-nucleate unreduced female gametophytes. The male gametophytes remain unaffected.
Flow cytometry was used to determine ploidy levels in the endosperm of both apomictic and sexual Tripsacum accessions. In both cases, fertilization appeared to involve only one sperm nucleus. Therefore, endosperm of apomictic Tripsacum develops normally even though the ratio of genomic contributions deviates from the normal 2m:1p ratio. Ratios of 2:1, 4:1,
4:2, 8:1 and 8:2 were observed, depending on both the ploidy level of the parents and the mode of reproduction. Thus, specific
dosage effects are seemingly not required for endosperm development in Tripsacum. These findings suggest that evolution of diplosporous apomixis might have been restricted to species with few or no imprinting
requirements, and the findings have strong implications regarding the transfer of apomixis to sexually reproducing crops.
Received: 17 February 1997 / Revision accepted: 7 July 1997 相似文献
10.
HPLC-UV and HPLC-MS investigations of phenolic acids and flavonoids in flowerheads of 84 samples of 76 taxa belonging to
66 species of Hieracium resulted in the identification of three phenolic acids (chlorogenic acid, 3,5-dicaffeoyl quinic acid, 4,5-dicaffeoyl quinic
acid) and six flavonoids (apigenin 4′-O-β-D-glucuronide, isoetin 4′-O-β-D-glucuronide, luteolin, luteolin 7-O-β-D-glucoside, luteolin 7-O-β-D-glucuronide, luteolin 4′-O-β-D-glucoside). The contents of these secondary metabolites were quantified by HPLC using quercetin and cynarin as internal
standards. In contrast to the previously investigated genera Leontodon and Crepis, cichoric acid and caffeoyl tartaric acid were not found in any of the investigated Hieracium taxa. Results of HPLC analyses revealed only a limited degree of qualitative variation between the different taxa, and luteolin
7-O-β-D-glucuronide and isoetin 4′-O-β-D-glucuronide were the only compounds, which were not detectable in some of the investigated taxa. Quantitative patterns
of phenolics differed markedly between particular taxa and Principal Component Analysis of the quantification results yielded
separate clusters for the members of the subgenera Hieracium and Pilosella.
Received January 23, 2001 Accepted October 11, 2001 相似文献
11.
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.
A cDNA fragment encoding a Lupinus albus. L. class-III chitinase, IF3, was isolated, using a cDNA probe from Cucumis sativus L., by in-situ plaque hybridization from a cDNA library constructed in the Uni-ZAP XR vector, with mRNAs isolated from mature
lupin leaves. The cDNA had a coding sequence of 293 amino acids including a 27-residue N-terminal signal peptide. A class-III
chitinase gene was detected by Southern analysis in the L. albus genome. Western blotting experiments showed that the IF3 protein was constitutively present during seed development and in
all the studied vegetative lupin organs (i.e., roots, hypocotyls and leaves) at two growth stages (7- and 20-d-old plants).
Accumulation of both the IF3 mRNA and IF3 protein was triggered by salicylic acid treatment as well as by abiotic (UV-C light
and wounding) and biotic stress conditions (Colletotrichum gloeosporioides infection). In necrotic leaves, IF3 chitinase mRNA was present at a higher level than that of another mRNA encoding a pathogenesis-related
(PR) protein from L. albus (a PR-10) and that of the rRNAs. We suggest that one role of the IF3 chitinase could be in the defense of the plant against
fungal infection, though our results do not exclude other functions for this protein.
Received: 15 March 1999 / Accepted: 12 July 1999 相似文献
14.
Calcium was localized in ovules of Plumbago zeylanica from 1 day before anthesis to 3 days after anthesis using potassium antimonate and transmission electron microscopy in pollinated
and emasculated flowers. At 1 day before anthesis, embryo sacs (containing an egg cell, a central cell and zero to three accessory
cells) appear mature and contain abundant calcium precipitates (ppts), in contrast to nucellar cells. At anthesis, the vacuoles
of nucellar cells have enlarged, and micropylar cells, in particular, are heavily labeled with calcium ppts. As pollen tubes
elongate through ovular tissues, ppts diminish in ovular cells and become concentrated in the pollen tube cell wall. After
fertilization, the calcium ppts sharply diminish in fertilized ovules; in unfertilized ovules, calcium ppts remain abundant
up to 3 days after anthesis (when unfertilized ovules are shed). The distribution of calcium in the ovule changes in apparent
response to fertilization, suggesting that calcium content may be related to the attraction and receipt of the pollen tube.
In contrast with conventionally-organized embryo sacs with synergids, Plumbago accumulates calcium in the egg cell.
Received: 30 December 1999 / Revision accepted: 24 March 2000 相似文献
15.
Microsporogenesis in Lilium longiflorum Thunb. is a naturally synchronous process and affords a system in which to study stage-specific events of meiosis and anther
development. Zymogram gel analyses were conducted with extracts from a variety of stages of anther development to identify
proteinases which likely play roles in anther metabolism. These experiments revealed that several proteinases are present
at different stages of anther development, and class-specific inhibitors were used to classify these enzymes. Proteolytic
activities increased as anther development proceeded and these activities were temporally correlated with the apoptotic events
which precede dehiscence, as well as with events crucial for the maturation of viable pollen.
Received: 12 October 1999 / Accepted: 13 November 1999 相似文献
16.
Effect of pollen source and pollen ploidy on endosperm formation and seed set in pseudogamous apomictic Paspalum notatum 总被引:3,自引:3,他引:0
Camilo L. Quarin 《Sexual plant reproduction》1999,11(6):331-335
It is generally accepted that most angiosperms require an accurate balance between maternal and paternal genome contribution
for endosperm development. The endosperm balance number (EBN) hypothesis postulates that each species has an effective number
which must be in a 2:1 maternal to paternal ratio for normal endosperm development and seed formation. The aim of this work
was to investigate the effect of different sources and ploidy levels of pollen donors on endosperm formation and seed production
of aposporous tetraploid (2n=4×=40) Paspalum notatum. Hand-emasculated spikelets of an apomictic 4× plant were dusted with pollen of 2×, 4×, 5×, 6× and 8× races of the same species;
3× and 4× races of a phylogenetically closely related species, P. cromyorrhizon; and 2× and 4× races of P. simplex, a species of a different subgenus. Experiments including self-pollination as well as emasculation without pollination were
conducted for controls. Results indicated that apomictic 4×P. notatum is a pseudogamous species with effective fertilization of the two unreduced (2n) polar nuclei by a reduced (n) sperm. Endosperm
development and seed production occurred independently of the species or the ploidy level of the pollen donor. However, seed
germination rates were significantly lower than in the self-pollinated control when the pollen donor was 3×P. cromyorrhizon or 2× and 4×P. simplex. Aposporous embryo sacs in Paspalum contribute to endosperm formation with two unreduced (2n) polar nuclei, while the male contribution is the same as in sexual
plants (n). Since sexual Paspalum plants fit the EBN hypothesis, the EBN insensitivity observed in apomictic plants might be a prerequisite for the spread
of pseudogamous apomixis. The EBN insensitivity could have arisen as an imprinting consequence of a high maternal genome contribution.
Received: 20 February 1998 / Revision accepted: 21 October 1998 相似文献
17.
Regulation and activation of phytoene synthase, a key enzyme in carotenoid biosynthesis, during photomorphogenesis 总被引:12,自引:0,他引:12
During photomorphogenesis in higher plants, a coordinated increase occurs in the chlorophyll and carotenoid contents. The
carotenoid level is under phytochrome control, as reflected by the light regulation of the mRNA level of phytoene synthase
(PSY), the first enzyme in the carotenoid biosynthetic pathway. We investigated PSY protein levels, enzymatic activity and
topological localization during photomorphogenesis. The results revealed that PSY protein levels and enzymatic activity increase
during de-etiolation and that the enzyme is localized at thylakoid membranes in mature chloroplasts. However, under certain
light conditions (e.g., far-red light) the increases in PSY mRNA and protein levels are not accompanied by an increase in
enzymatic activity. Under those conditions, PSY is localized in the prolamellar body fraction in a mostly enzymatically inactive
form. Subsequent illumination of dark-grown and/or in far-red light grown seedlings with white light causes the decay of these
structures and a topological relocalization of PSY to developing thylakoids which results in its enzymatic activation. This
light-dependent mechanism of enzymatic activation of PSY in carotenoid biosynthesis shares common features with the regulation
of the NADPH:protochlorophyllide oxidoreductase, the first light-regulated enzyme in chlorophyll biosynthesis. The mechanism
of regulation described here may contribute to ensuring a spatially and temporally coordinated increase in both carotenoid
and chlorophyll contents.
Received: 14 February 2000 / Accepted: 15 March 2000 相似文献
18.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
19.
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
20.
The mechanical properties of young stems of Aristolochia macrophylla Lam. and Aristolochia brasiliensis Mart. et Zucc. were studied during elongation growth and primary differentiation. Data for the modulus of elasticity, for
the viscoelastic behaviour caused by longitudinal tension and for the shear modulus resulting from torsion around a longitudinal
axis were related to the underlying structural changes by quantitative analysis of stem anatomy, tissue distribution, ultrastructure,
and cell wall biochemistry. The orientation of cellulose microfibrils was determined by light microscopy and small-angle X-ray
diffraction, and the lignin content was determined by thioglycolic acid derivatization and spectroscopic quantification. It
was demonstrated that the increase in stability during early development is due to the complementary effects of increase in
cell wall material, lignification, and cellulose microfibril alignment. A detailed micromechanical model, considering internal
prestresses, is proposed to explain the characteristic biphasic stress-strain behaviour as well as the strain-hardening observed.
Received: 22 March 1999 / Accepted 9 September 1999 相似文献