共查询到20条相似文献,搜索用时 15 毫秒
1.
Kirakosyan A Kaufman PB Chang SC Warber S Bolling S Vardapetyan H 《Plant cell reports》2006,25(12):1387-1391
A mini-hydroponic growing system was employed for seedlings of kudzu vine (Pueraria montana) and contents of isoflavones (daidzein, genistein, daidzin, genistin, and puerarin) from shoot and root parts of seedlings were analyzed quantitatively. In addition, exogenous cork pieces, polymeric adsorbent, XAD-4, and universal elicitor, methyl jasmonate (MeJA), were used to regulate the production of these isoflavones. It was shown that cork pieces up-regulate the production of daidzein and genistein up to seven- and eight-fold greater than the levels obtained for control roots. In contrast, levels of glucosyl conjugates, daidzin and genistin, decrease up to five- and eight-fold, respectively. Cork treatment also induces the excretion of the root isoflavone constituents into the growth medium. Minimal levels of isoflavones are absorbed by the cork pieces. XAD-4 stimulates the production of glucosyl conjugates, daidzin and genistin, in root parts about 1.5-fold greater than that obtained in control roots. These are the highest amounts of daidzin and genistin that are observed (5.101 and 6.759 mg g−1 dry weight, respectively). In contrast to these two adsorbents, MeJA increases the accumulation of isoflavones in shoot rather than in root parts of seedlings, about three- to four-fold over control levels, with the exception of genistein. These studies reveal new observations on the regulation of isoflavone production in hydroponically grown Pueraria montana plants by two adsorbents (cork pieces and XAD-4) and MeJA elicitor. 相似文献
2.
Stimulation of the production of hypericins by mannan in Hypericum perforatum shoot cultures 总被引:2,自引:0,他引:2
Shoot organ cultures were established from callus derived from anthers of Hypericum perforatum flowers and the effect of elicitors on hypericin and pseudohypericin production in shoot organ cultures was investigated. Mannan stimulated pseudohypericin production up to four fold (0.82 mg/g dry wt) and hypericin production up to two fold (0.04 mg/g dry wt.) beta-1,3-glucan and pectin slightly stimulated pseudohypericin production (ca. two fold), but had no effect on hypericin production. On the other hand, yeast extract showed no stimulatory effect, on either hypericin or pseudohypericin production. 相似文献
3.
Sonja Gadzovska Stéphane Maury Saida Ounnar Michel Righezza Slavka Kascakova Matthieu Refregiers Mirko Spasenoski Claude Joseph Daniel Hagège 《Plant Physiology and Biochemistry》2005,43(6):591-601
Investigations have been made to develop an efficient protocol for micropropagation allowing to improve hypericin and pseudohypericin productions in Hypericum perforatum L. in vitro cultures. The role of growth regulator treatments has been particularly studied. Three in vitro culture lines with different morphological characteristics were obtained during H. perforatum micropropagation and referred to shoots, calli and plantlets according to their appearance. Multiplication and callogenesis from apical segments from sterile germinated seedlings were obtained on solid MS/B5 culture medium in the presence of N6-benzyladenine (BA) (0.1-5.0 mg/l BA). Regenerative potential of shoots was assessed on medium supplemented with auxins (0.05-1.0 mg/l), indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA). The main goal of the research was to summarize the influence of plant growth regulators on hypericin and pseudohypericin productions in in vitro cultures of Hypericum. A rapid method for naphtodianthrone quantification was developed. The use of a reversed-phase high performance liquid chromatography (HPLC) method with fluorescence detection was used. Identification of the compounds was confirmed by electrospray ionization-mass spectrometry (ESI-MS) with electrospray in negative ion mode [M-H] . Calli, shoots and plantlets of H. perforatum produced hypericin and pseudohypericin. The concentration range of BA from 0.1 to 2.0 mg/l improved the production of hypericin (25-50 microg/g dry mass (DM)) and pseudohypericin (170-350 microg/g DM) in shoots. In callus cultures, BA (4.0-5.0 mg/l) did not changed hypericin contents (15-20 microg/g DM) but influenced pseudohypericin productions (120-180 microg/g DM). In the presence of auxins (IAA and IBA), Hypericum plantlets produced hypericin (30-100 microg/g DM) and pseudohypericin (120-400 microg/g DM). The presence of IAA did not influence naphtodianthrone productions in plantlets, but IBA decreased hypericin and pseudohypericin amounts in plantlets. The specific accumulation of the naphtodianthrones in in vitro cultures was influenced by phytohormonal supplementation of the medium. Results indicated that the production of hypericin and pseudohypericin could be increased by carefully adapted in vitro cultures. Hypericum in vitro cultures represent promising systems for hypericin and pseudohypericin productions. 相似文献
4.
The genus Hypericum has received considerable interest from scientists, as it contains the variety of structurally diverse natural products which possess a wide array of biological properties, mainly hypericins and hyperforin. In the present study, variations of pseudohypericin and hyperforin were investigated in two Turkish species of Hypericum, namely Hypericum perfoliatum and Hypericum origanifolium. Wild growing plants were harvested at vegetative, floral budding, flowering, fresh fruiting and mature fruiting stages, and dissected into stem, leaf and reproductive tissues and assayed for chemical contents by high performance liquid chromatography method. Content of pseudohypericin and hyperforin in samples of the whole plant increased during the course of ontogenesis in both species. The highest levels of the chemicals were reached at full flowering (2.62 mg/g dry weight (DW) pseudohypericin and 1.84 mg/g DW hyperforin for H. perfoliatum; 0.93 mg/g DW pseudohypericin and 1.63 mg/g DW hyperforin for H. origanifolium). Among different reproductive parts, full opened flowers produced the highest amount of pseudohypericin (1.18 mg/g DW) and hyperforin (4.36 mg/g DW) in H. origanifolium. Similarly, the highest pseudohypericin accumulation was observed in full opened flowers in H. perfoliatum (7.41 mg/g DW) while floral buds of this species produced the highest amount of hyperforin (7.80 mg/g DW). These data can be useful when elucidating the medicinal properties of the species and the chemosystematic significance of hyperforin and pseudohypericin in the relationships among species of Hypericum. 相似文献
5.
The effects of thidiazuron (TDZ) on adventitious bud and shoot formation from hypocotyl segments of sweetgum (Liquidambar styracifiua) were tested alone and in combination with 2,4-dichlorophenoxyacetic acid (2,4-D). The combination of 1 mg/1 TDZ with 0.01 mg/l 2,4-D resulted in the highest frequency of bud production. Lower concentrations of TDZ stimulated shoot production, generating the most shoots at 0.1 mg/1 TDZ with 0.01 mg/1 of 2,4-D. Inhibition of shoot elongation by TDZ was overcome by transferring shoot cultures to a shoot proliferation medium lacking TDZ or containing naphthaleneacetic acid and benzyladenine in addition to TDZ. Shoot production in liquid culture was significantly greater than that in solid culture. Comparisons of in vitro and ex vitro rooting of the adventitious shoots demonstrated that ex vitro rooting produced plants with faster growth rates and more extensive root systems.Abbreviations
BA
Benzyladenine
-
IBA
indole-3-butyric acid
-
NAA
naphthaleneacetic acid
-
PGR
plant growth regulator
-
TDZ
thidiazuron
-
2,4-D
2,4-dichlorophenoxyacetic acid 相似文献
6.
P. Surový A. Olbrich A. Polle N. A. Ribeiro B. Sloboda R. Langenfeld-Heyser 《Trees - Structure and Function》2009,23(6):1237-1246
A new method for measuring annual growth rings in cork has been developed. It is based on the fact that excitation of Quercus suber L. cork cross-sectional planes with UV light and also with blue light results in enhanced autofluorescence at the growth
ring borders. This distinct autofluorescence band is located in the cork produced at the end of the vegetation period, with
its smaller cells and thicker cell walls. The enhanced autofluorescence of polyphenolics mainly results from a very thick
suberin layer in the walls of the small late cork cells. The gradient in autofluorescence from late cork to first early cork
is steep. The best visibility of cork annual rings was found under the epifluorescence microscope in 60 μm thick microtome
cork cross sections. For fast screening of high sample numbers scanning the blue-excited (473 nm) fluorescence of water wetted
polished cross-sectional surfaces of cork pieces with a laser-equipped fluorescence image analyzer was most suitable. Evaluation
of visibility of cork rings showed a clear improvement in comparison with reflected light image analysis; thus data obtained
with this new autofluorescence scanning method are excellent for modeling the yearly growth increment of cork. 相似文献
7.
H. R. Vardapetyan A. A. Oganesyan E. E. Kabasakalyan S. G. Tiratsuyan 《Russian Journal of Developmental Biology》2006,37(6):350-353
We studied the effects of elicitors, such as mannan, gβ-1,3-glucan, ancymidol, and cork crumbs, on morphogenetic and biosynthetic potencies of shoot cultures of Hypericum perforatum L. In the presence of these elicitors, different morphogenetic structures of H. perforatum callus cultures were formed. A correlation was found between the morphogenetic processes and induction of hypericin and pseudohypericin biosynthesis in the callus cultures. 相似文献
8.
We studied the effects of elicitors, such as mannan, beta-1,3-glucan, ancymidol, and cork crumbs, on morphogenetic and biosynthetic potencies of shoot cultures of Hypericum perforatum L. In the presence of these elicitors, different morphogenetic structures of H. perforatum callus cultures were formed. A correlation was found between the morphogenetic processes and induction of hypericin and pseudohypericin biosynthesis in the callus cultures. 相似文献
9.
Cristina Silva Pereira Giselle A. M. Soares Ana C. Oliveira Maria Emília Rosa Helena Pereira Nuno Moreno Maria Vitria San Romo 《International biodeterioration & biodegradation》2006,57(4):244-250
The industrialization of traditional processes relies on the scientific ability to understand the empirical evidence associated with traditional knowledge. Cork manufacturing includes one operation known as stabilization, where humid cork slabs are extensively colonized by fungi. The implications of fungal growth on the chemical quality of cork through the analysis of putative fungal metabolites have already been investigated. However, the effect of fungal growth on the mechanical properties of cork remains unexplored. This study investigated the effect of cork colonization on the integrity of the cork cell walls and their mechanical performance. Fungal colonization of cork by Chrysonilia sitophila, Mucor plumbeus Penicillium glabrum, P. olsonii, and Trichoderma longibrachiatum was investigated by microscopy. Growth occurred primarily on the surface of the cork pieces, but mycelium extended deeper into the cork layers, mostly via lenticular channels and by hyphal penetration of the cork cell wall.In this first report on cork decay in which specific correlation between fungal colonization and mechanical proprieties of the cork has been investigated, all colonizing fungi except C. sitophila, reduced cork strength, markedly altering its viscoelastic behaviour and reducing its Young's modulus. 相似文献
10.
Hypericum perforatum L. (St. John’s wort) and Hypericum sampsonii Hance are medicinal plants used in China in the treatment of viruses and other disorders. In the current study, we investigated
the effects of cytokinins 6-benzylaminopurin (BA), zeatin (ZT) and thidiazuron (TDZ) on plant growth and production of hypericins
(pseudohypericin and hypericin) and hyperforin. Our data suggested that culture of H. perforatum in modified MS (Murashige and Skoog) medium, with a 50% reduction in ammonium nitrate and potassium nitrate, and supplemented
with BA (0.44 μM) and indolebutyric acid (IBA, 0.049 μM), resulted in increased production of hypericins. Similar results
were noted with H. sampsonii with minor changes to the medium (0.46 μM ZT and 0.049 μM IBA). There were approximately 2.95-, 2.62-fold increases in H. perforatum pseudohypericin and hypericin production by TDZ (0.45 μM) induction compared to the controls. No enhancement of hypericins
and hyperforin production was elicited by TDZ in H. sampsonii. The elicitor methyl jasmonate (MJA, 50 μM) and its analog, 2,3-dihydroxypropyl jasmonate (DHPJA, 50 μM), were also used
in H. perforatum and H. sampsonii shoot culture to increase secondary metabolite production, eliciting an increase in the production of hypericins and hyperforin.
While leaf senescence and biomass inhibition were observed in cultures induced by MJA, no such effects were observed with
DHPJA. 相似文献
11.
Plant regeneration in Arachis pintoi was obtained via two developmental pathways: organogenesis and somatic embryogenesis. Organogenic callus cultures were initiated
from pieces of leaf on MS medium supplemented with NAA or 2,4-D in combination with BA, KIN or 2iP. The most suitable combination
for plant regeneration through organogenesis was an initial medium composed of 10 mg/l NAA+1 mg/l BA followed by transfer
of the callus to a shoot induction medium (MS+1 mg/l BA). Rooting of regenerated shoots was readily achieved by culture on
MS+0.01 mg/l NAA. Embryogenic callus cultures were initiated from pieces of leaf on MS medium supplemented with PICL in combination
with KIN, ZEA, BA or 2iP, and the most suitable combinations were 20 mg/l PICL+1 mg/l BA or 2iP. When pieces of embryogenic
callus were subcultured on MS+1 mg/l BA, somatic embryos were differentiated and developed further into well-developed plants
in MS+1 g/l AC followed by MS medium devoid of plant growth regulators.
Received: 29 April 1999 / Revision received: 24 November 1999 / Accepted: 18 December 1999 相似文献
12.
Vasil Georgiev Ivan Ivanov Strahil Berkov Mladenka Ilieva Milen Georgiev Tatiana Gocheva Atanas Pavlov 《Engineering in Life Science》2012,12(5):534-543
Shoot culture of summer snowflake (Leucojum aestivum L.) was successfully cultivated in an advanced modified glass‐column bioreactor with internal sections for production of Amaryllidaceae alkaloids. The highest amounts of dry biomass (20.8 g/L) and galanthamine (1.7 mg/L) were achieved when shoots were cultured at 22°C and 18 L/(L·h) flow rate of inlet air. At these conditions, the L. aestivum shoot culture possessed mixotrophic‐type nutrition, synthesizing the highest amounts of chlorophyll (0.24 mg/g DW (dry weight) chlorophyll A and 0.13 mg/g DW chlorophyll B). The alkaloids extract of shoot biomass showed high acetylcholinesterase inhibitory activity (IC50 = 4.6 mg). The gas chromatography–mass spectrometry (GC/MS) profiling of biosynthesized alkaloids revealed that galanthamine and related compounds were presented in higher extracellular proportions while lycorine and hemanthamine‐type compounds had higher intracellular proportions. The developed modified bubble‐column bioreactor with internal sections provided conditions ensuring the growth and galanthamine production by L. aestivum shoot culture. 相似文献
13.
J. L. Vandemoortele J. P. Billard J. Boucaud T. Gaspar 《In vitro cellular & developmental biology. Plant》1999,35(1):13-17
Summary Leafy shoots of cauliflower were produced from hypocotyl segments, curd branches (debarassed of existing meristems) and intact
curd pieces submitted to various basal media. Adventitious shoot production and axillary bud break exhibited very different
nutritive requirements. In each case, an interaction between the plant growth regulators and the composition of the basal
medium was discovered. Propagation from curd pieces was dependent on the interaction between plant growth regulators and high
sucrose-to-macronutrients ratio in the medium. A medium containing 168 mM sucrose, supplemented with 2.5 μM N6-benzyladenine and 5 μM naphthaleneacetic acid allowed the production of numerous shoots without any hyperhydric symptoms. 相似文献
14.
Hu Zhong Guo Guang-Qin Zhao Dong-Li Li Li-Hua Zheng Guo-Chang 《Russian Journal of Plant Physiology》2001,48(4):453-458
A method for fast plant regeneration via organogenesis directly from Lycium barbarumleaf explants has been developed. The key factor for shoot regeneration was the presence of benzyladenine (BA) in the medium. NAA could only induce root formation and explant callusing. Murashige and Skoog (MS) medium supplemented with 2 mg/l BA and 0.5 mg/l NAA is the most efficient condition for shoot formation, with up to 92.6% shoot regeneration and no callus formation. All adventitious shoots cultured on MS medium supplemented with 1 mg/l IAA formed an extensive root system. Regenerated plants were morphologically normal and were also proved to be diploid (2n = 24). Using the optimized regeneration system, the genetic transformation of L. barbarumwas carried out mediated by Agrobacterium tumefaciensEHA101(pIG121Hm). 11.8% leaf explants produced kanamycin-resistant shoots after infection by A. tumefaciens.The putative transgenic nature of plants was confirmed by GUS assay and PCR analysis. Expression of the nptIIgene in the regenerated plants was also detected by observing the callus formation by leaf pieces on MS medium containing 0.2 mg/l 2,4-D and 0–100 mg/l kanamycin. 相似文献
15.
Ana Coste Laurian Vlase Adela Halmagyi Constantin Deliu Gheorghe Coldea 《Plant Cell, Tissue and Organ Culture》2011,106(2):279-288
We investigated the effects of plant growth regulators [6-benzyladenine (BA), kinetin (Kin), 6-γ,γ-dimethylallylaminopurine
(2iP), thidiazuron (TDZ) and α-naphthaleneacetic acid (NAA)], modified Murashige and Skoog (MS) medium containing 10 mM NH4
+ and 5 mM NO3
− and supplemented with 2iP, BA, Kin and NAA (MSM medium), and two elicitors [jasmonic acid (JA), and salicylic acid (SA)],
on plant growth and accumulation of hypericins (hypericin and pseudohypericin) and hyperforin in shoot cultures of Hypericum hirsutum and H. maculatum. Our data suggested that culture of shoots on MS medium supplemented with BA (0.4 mg l−1) or Kin (0.4 mg l−1) enhanced production of hypericins in H. maculatum and hyperforin in H. hirsutum. Hypericins and hyperforin concentrations decreased in both species when TDZ (0.4 mg l−1) was added to the MS medium. Also, TDZ induced hyperhydric malformations and necrosis of regenerated shoots. Cultivation
of H. maculatum on MSM medium resulted in approximately twofold increased production of hypericins compared to controls, and the growth of
H. hirsutum shoots on the same medium led to a 6.16-fold increase in hyperforin production. Of the two elicitors, SA was more effective
in stimulating the accumulation of hypericins. At 50 μM, SA enhanced the production of hypericin (7.98-fold) and pseudohypericin
(13.58-fold) in H. hirsutum, and, at 200 μM, enhanced the production of hypericin (2.2-fold) and pseudohypericin (3.94-fold) in H. maculatum. 相似文献
16.
Xiao-Na Liu Xiu-Qing Zhang Shi-Xiang Zhang Jun-She Sun 《Plant Cell, Tissue and Organ Culture》2007,91(1):1-7
Four precursors (l-phenylalanine, l-tryptophan, cinnamic acid and emodin) and one signal elicitor (methyl jasmonate, MeJA) were added to liquid cultures of Hypericum perforatum L. to study their effect on production of hyperforin and hypericins (pseudohypericin and hypericin). The addition of l-phenylalanine (75 to 100 mg l−1) enhanced production of hypericins, but hyperforin levels were decreased. Hypericin, pseudohypericin and hyperforin concentrations
were all decreased when l-tryptophan (25 to 100 mg l−1) was added to the medium. However, addition of l-tryptophan (50 mg l−1) with MeJA (100 μM) stimulated hyperforin production significantly (1.81-fold) and resulted in an increased biomass. Cinnamic acid (25, 50 mg l−1) and emodin (1.0 to 10.0 mg l−1) each enhanced hyperforin accumulation in H. perforatum, but did not affect accumulation of hypericins. 相似文献
17.
Fouquieria splendens, a desert plant native to the southwestern United States, was studied to determine the capacity for photosynthesis of green stem tissue. The plant is leafless most of the year because of drought, so the capacity for gas exchange by the stems is essential for their photosynthetic function. With secondary growth, sclerified leaf bases which cover the stem become separated, and a transparent cork forms in the furrows between them. A well-developed chlorenchyma occurs beneath this cork as well as beneath the leaf bases. Chloroplasts of the stem have an unusually high degree of granal stacking, but are mostly typical. Light is transmitted through the leaf base on the young primary shoot and the furrow cork, but not through the older leaf base. Chlorophyll fluorescence studies indicated that the chloroplasts were fully competent and indeed stem tissue is capable of fixing 14CO2 if supplied to cut sections. Despite competent chloroplasts, no exogenous CO2 uptake occurs because the cork is impermeable to CO2, and presumably water. The functional significance of competent chloroplasts in stems that do not transfer gas may be the production of high energy compounds for metabolism, the recycling of internally generated respiratory CO2, or it may simply be a relictual feature in this species of the Fouquieriaceae. 相似文献
18.
Ekrem Gurel Buhara Yucesan Esra Aglic Songul Gurel Sandeep K. Verma Munevver Sokmen Atalay Sokmen 《Plant Cell, Tissue and Organ Culture》2011,104(2):217-225
A high-frequency in vitro regeneration of Digitalis davisiana Heywood (Alanya foxglove) and cardiotonic glycoside production from both in vitro produced materials (regenerated plantlets
or germinated seedlings) and leaves of natural populations were obtained. Cardiac glycosides regulate heart rhythm and are
effective in cancer chemotherapy, in particular for prostate and breast cancer treatments. Testing six different types of
culture media revealed that Linsmaier and Skoog (LS) was the most effective for shoot production. Shoot regeneration efficiency
was higher when flamingo-bill or hypocotyl explants were cultured on LS medium containing 0.5 mg/l thidiazuron (TDZ) and 0.25 mg/l
indoleacetic acid (IAA). Rooting of all shoots that regenerated was readily achieved, even in the absence of plant growth
regulators (PGRs). Production of cardenolides (lanatoside C and digoxin) in the materials grown in vitro seemed to correlate
with several parameters, such as nutritional and hormonal compositions of the culture medium as well as the duration of culture
on the initial regeneration and/or final growth medium. Higher amounts of digoxin accumulation were obtained when shoots were
regenerated on LS or Gamborg’s B5 medium containing 0.5 mg/l TDZ and 0.25 mg/l IAA, producing 12.59 and 11.93 mg/kg dry weight
(dw) digoxin, respectively. For natural populations, seasonal variations seemed to affect the production of digoxin in the
leaves. The highest amount of digoxin (246.58 mg/kg dw) was in leaf samples collected in July, which coincides with the flowering
stage of the plant in the region of collection. 相似文献
19.
Ari Kornfeld Peter B Kaufman Casey R Lu Donna M Gibson Steven F Bolling Sara L Warber Soo Chul Chang Ara Kirakosyan 《Plant Physiology and Biochemistry》2007,45(1):24-32
In vitro shoot cultures of Hypericum perforatum derived from wild populations grown in Armenia have a wide variation of hypericin and pseudohypericin metabolite content. We found that a germ line denoted as HP3 produces six times more hypericin and fourteen times more pseudohypericin than a second line labeled HP1. We undertook a structural comparison of the two lines (HP1 and HP3) in order to see if there are any anatomical or morphological differences that could explain the differences in production of these economically important metabolites. Analysis by LM (light microscopy), SEM (scanning electron microscopy), and TEM (transmission electron microscopy) reveals that the hypericin/pseudohypericin-containing black glands located along the margins of the leaves consist of a peripheral sheath of flattened cells surrounding a core of interior cells that are typically dead at maturity. The peripheral cells of the HP3 glands appear less flattened than those of the HP1 glands. This may indicate that the peripheral cells are involved in hypericin/pseudohypericin production. Furthermore, we find that these peripheral cells undergo a developmental transition into the gland's interior cells. The fact that the size of the peripheral cells may correlate with metabolite production adds a new hypothesis for the actual site of hypericin synthesis. 相似文献
20.
C Silva Pereira A Pires M J Valle L Vilas Boas J J Figueiredo Marques M V San Romão 《Journal of industrial microbiology & biotechnology》2000,24(4):256-261
The contribution of Chrysonilia sitophila in cork stopper manufacture was studied and a simulation of the industrial processing of cork stoppers was performed. Stoppers
cut from slabs where mold development was inhibited were compared with others cut from slabs colonized by C. sitophila alone or with several molds, in terms of physical properties and chemical taints. C. sitophila does not produce 2,4,6-trichloroanisole, guaiacol, or 1-octene-3-ol on cork slabs incubated for 66 days. Since some chlorophenol-related
compounds contaminate cork slabs during the production processes, metabolic tests were performed to investigate the capability
of molds to produce 2,4,6-trichloroanisole by methylation of 2,4,6-trichlorophenol. Degradation of 2,4,6-trichlorophenol by
C. sitophila resulted in a very high level of degradation without production of 2,4,6-trichloroanisole. C. sitophila restricted growth of other molds on maturing slabs for at least 30 days. These results show that C. sitophila can be exploited by industrial producers of cork stoppers since it is able to inhibit the development of other molds and
it does not produce the compounds responsible for ‘cork-taint’, even in the presence of chlorophenols. Journal of Industrial Microbiology & Biotechnology (2000) 24, 256–261.
Received 28 July 1999/ Accepted in revised form 05 January 2000 相似文献