共查询到20条相似文献,搜索用时 15 毫秒
1.
Zhijian Li Abdoulaye Traore Siela Maximova Mark J. Guiltinan 《In vitro cellular & developmental biology. Plant》1998,34(4):293-299
Summary A procedure for the regeneration of cacao (Theobroma cacao) plants from staminode explants via somatic embryogenesis was developed. Rapidly growing calli were induced by culturing
staminode explants on a DKW salts-based primary callus growth (PCG) medium supplemented with 20 g glucose per L, 9 μM 2,4-D, and thidiazuron (TDZ) at various concentrations. Calli were subcultured onto a WPM salts-based secondary callus growth
medium supplemented with 20 g glucose per L, 9 μM 2,4-D, and 1.4 nM kinetin. Somatic embryos were formed from embryogenic calli following transfer to a hormone-free DKW salts-based embryo development
medium containing sucrose. The concentration of TDZ used in PCG medium significantly affected the rate of callus growth, the
frequency of embryogenesis, and the number of somatic embryos produced from each responsive explant. A TDZ concentration of
22.7 nM was found to be the optimal concentration for effective induction of somatic embryos from various cacao genotypes. Using
this procedure, we recovered somatic embryos from all 19 tested cacao genotypes, representing three major genetic group types.
However, among these genotypes, a wide range of variation was observed in both the frequency of embryogenesis, which ranged
from 1 to 100%, and the average number of somatic embryos produced from each responsive explant, which ranged from 2 to 46.
Two types of somatic embryos were identified on the basis of their visual appearance and growth behavior. A large number of
cacao plants have been regenerated from somatic embryos and established in soil in a greenhouse. Plants showed morphological
and growth characteristics similar to those of seed-derived plants. The described procedure may allow for the practical use
of somatic embryogenesis for clonal propagation of elite cacao clones and other applications that require the production of
a large number of plants from limited source materials. 相似文献
2.
Developmental anomalies in the plumule meristem of peanut (Arachis hypogaea L.) somatic embryos resulted in poor shoot differentiation and reduced plant recovery. Existing meristems with caulogenic
potential have never been tested for embryogenesis in peanut. The present experiment was designed to test the mature zygotic
embryo axis derived plumule with three meristems for somatic embryogenesis. Embryogenic masses and embryos developed from
the caulogenic meristems in the axils. Exposure of 2 weeks in primary medium with 90.5 μM 2,4-D suppressed the shoot tip differentiation
temporarily which then regained the ability to form the shoot on withdrawal of 2,4-D. Exposure of 4 weeks in primary medium
with 90.5 μM 2,4-D suppressed the shoot tip differentiation irreversibly. No shoot formation was noted from the tips in any
of the cultures which were in secondary medium with 13.6 μM 2,4-D. Development of somatic embryos directly from axillary meristems
was confirmed histologically. Conversion frequency of these embryos was 11%. Thus, in this report, we describe a method to
obtain somatic embryos from the determined organogenic buds of the axillary meristem, by culturing the nodal explant vertically
on embryo induction medium. It also displays the possibility of obtaining both embryogenic and organogenic potential in two
parts of the same explant simultaneously. The possibility of extending this approach for genetic transformation in in vivo
system through direct DNA delivery or Agrobacterium injection in meristems can also be explored. Using Agrobacterium rhizogenes, we have demonstrated the possibility of gene transfer in the axillary meristems of seed-derived plumule explant. 相似文献
3.
The somatic embryogenesis potential of zygotic embryo axes of peanut (Arachis hypogaea L. cv. DRG-12) at different stages of development was evaluated by culturing on MS medium with 18.1 μM 2,4-dichlorophenoxyacetic acid (2,4-D). A 100 % frequency with 18.3 somatic embryos per explant was observed from 4 mm long immature zygotic embryo axes collected 31 – 40 d after pollination. Medium supplemented with 16.6 μM picloram resulted in slow development of somatic embryos whereas in the presence of 21.5 μM α-naphthaleneacetic acid (NAA), the explants underwent maturation with induction of roots after 30 d. The changes in protein profiles in zygotic embryo axes at different stages of development correlated with their potential to form somatic embryos. Immature zygotic embryo axes exhibited high frequency somatic embryogenesis in the stage preceding abundant accumulation of 22 and 65 kDa proteins. The content of 22 and 65 kDa proteins decreased immediately after culture on medium fortified with 18.1 μM 2,4-D and increased again after 12 d of culture coinciding with the development of somatic embryos on the explants. The content of 22 and 65 kDa proteins was low at 15 d of culture on medium supplemented with 16.6 μM picloram possibly due to slow development of the somatic embryos on the explant. On maturation medium containing 21.5 μM NAA, a marked increase in the content of 22 and 65 kDa proteins in 15 d-old cultures was observed. 相似文献
4.
Charleen M. Baker Richard E. Durham J. Austin Burns Wayne A. Parrott Hazel Y. Wetzstein 《Plant cell reports》1995,15(1-2):38-42
Peanut (Arachis hypogaea L.) somatic embryos were produced from the embryo axes of mature, dry seeds of cultivar GK-7. Percent embryogenic explants ranged from 88–100% using 10–40 mg/1 of 2,4-D in the induction medium. Neither 2,4-D concentration nor photoperiod during the induction period had a large effect on percent embryogenesis, mean number of embryos per explant, or embryo morphology. However, embryos obtained from cultures grown in the dark were easier to remove from the explant than those under a 16-h photoperiod. Somatic embryos developed on the epicotyl portion of the embryo axis, primarily on the young, expanding leaves. A survey of 14 genotypes indicated that genotype had a large influence on embryogenic capacity, with all genotypes being embryogenic to some extent. The ability to recover somatic embryos from axes of harvested, stored seeds represents significant advantages for the establishment of peanut embryogenic cultures, including the use of simple sterilization procedures and a constant source of explant tissue.Abbreviations B5
medium of Gamborget al. (1968)
- 2,4-D
2,4-dichlorophenoxyacetic acid
- MS
Murashige and Skoog (1962) salts medium 相似文献
5.
E. Sofiari C.J.J.M. Raemakers E. Kanju K. Danso A.M. van Lammeren E. Jacobsen R.G.F. Visser 《Plant Cell, Tissue and Organ Culture》1997,50(1):45-56
NAA and 2,4-D were compared for their ability to induce somatic embryogenesis in cassava (Manihot esculenta Crantz). In all seven cultivars tested, only 2,4-D had the capacity to induce primary somatic embryos from leaf explants,
however, both NAA and 2,4-D were capable of inducing secondary somatic embryos. More secondary somatic embryos were formed
in NAA than in 2,4-D medium. Furthermore, the maturation period for secondary somatic embryos was shorter in NAA medium than
in 2,4-D medium. In some cultivars, repeated subculture of secondary somatic embryos in NAA medium resulted in a gradual shift
from somatic embryogenesis to adventitious root formation. This shift could be stopped and reversed by subculture of the material
in 2,4-D medium. In NAA medium the most secondary somatic embryos were formed when they were subcultured every 15 days whereas
in 2,4-D a 20 day subculture interval was optimal. Subculture of secondary somatic embryos at a high inoculum density (>1.5
g jar−1) in NAA medium did not result in the formation of secondary somatic embryos, whereas in 2,4-D it lead to the formation of
globular secondary somatic embryos. With 2,4-D the newly induced secondary somatic embryos were connected vertically to the
explant and with NAA medium horizontally. For all cultivars tested, desiccation stimulated normal germination of NAA-induced
somatic embryos. However, the desiccated, secondary somatic embryos required a medium supplemented with BA for high frequency
germination. The concentration of BA needed for high frequency germination was higher when the desiccated secondary somatic
embryos were cultured in light instead of dark. In only one cultivar desiccation enhanced germination of 2,4-D induced secondary
somatic embryos and in three other cultivars it stimulated only root formation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
6.
Auxin pulse treatment holds the potential to enhance efficiency and practicability of somatic embryogenesis in potato 总被引:1,自引:1,他引:0
The objective of the current study was to simplify existing somatic embryogenesis systems in potato (Solanum tuberosum L.) cv. Desiree. The project targeted the agar-based induction phase of the potato somatic embryogenesis process as the key
area for improvement. Experiments were established to ascertain the effect of a 2,4-D (2,4 dichlorophenoxyacetic acid) pulse,
applied to the primary internodal section explant source and its subsequent effect on embryo induction. Parameters tested
were the duration of the auxin pulse in a range from 0 to 300 min, and the concentrations of 2,4-D applied, in a range from
0 to 5,120 μM. The mean number of somatic embryos formed per explant was recorded after 4 and 8 weeks culture. Our findings
indicated that the somatic embryogenesis in potato internodal segments could be evoked by an auxin (2,4-D) pulse treatment
over a wide concentration and duration range. The results further suggested that a simple 20 μM 2,4-D pulse treatment could
replace a lengthy 2 week induction phase in potato somatic embryogenesis and thus improve the system’s practicability for
wider uptake. 相似文献
7.
Direct somatic embryogenesis of Frittilaria meleagris L. was induced using leaf base explants excised from in vitro grown shoots. Somatic embryos occurred at the basal part of leaf explants 4 weeks after culture on a Murashige and Skoog
(MS) medium supplemented with various concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) or kinetin (KIN). The highest
number of somatic embryos (SEs) were formed (9.74) from leaf explant on MS medium supplemented with 0.1 mg dm−3 2,4-D after 4 weeks of culture initiation. An initial exposure to a low concentration of KIN in the medium also enhanced
SEs induction. Our observations by light and scanning electron microscopy revealed that SEs originate directly from the epidermal
and subepidermal layers of leaf explant. The developmental stages of somatic embryogenesis from the first unequal cell division
through the meristematic clusters, multi-cellular globular somatic embryos to the fully formed cotyledonary embryos were determined.
After 4 weeks on MS medium without plant growth regulators, SEs developed into bulblets. 相似文献
8.
Alejandro Nuño-Ayala Benjamín Rodríguez-Garay Antonia Gutiérrez-Mora 《Plant Cell, Tissue and Organ Culture》2012,109(1):33-39
It is reported for the first time an efficient protocol for indirect somatic embryogenesis and plant regeneration for Jarilla heterophylla (Caricaceae). Initial explants were mature zygotic embryos obtained from seeds collected in two regions of the state of Jalisco,
México (San Luis Soyatlán and Zacoalco de Torres). Two protocols for somatic embryogenesis used previously for Carica papaya were evaluated. The addition of 2,4-dichlorophenoxyacetic acid (2,4-D) to induction medium A1 without the addition of adenine
hemisulphate yielded the best production of embryogenic callus with the higher total of somatic embryos per explant. With
this protocol the plant regeneration process took about five months. 相似文献
9.
Summary A protocol was developed for high frequency somatic embryogenesis and plant regeneration from cotyledon and hypocotyl explants
of Eruca sativa. Explants grown on Murashige and Skoog (MS) medium supplemented with 4.52 μM 2,4-D formed embryogenic callus after 4 wk of culture. Secondary somatic embryos were also produced from primary somatic
embryos on MS medium containing 0.56 μM 2,4-D. Somatic embryos developed into mature embryos on MS medium in the presence of 45 gl−1 polyethylene glycol. After desiccation, somatic embryos developed into plantlets by culturing the mature somatic embryos
on 1/2 x MS medium containing 0.24 μM indole-3-butyric acid. 相似文献
10.
W. A. Parrott 《Plant cell reports》1991,10(1):17-21
Cotyledons from immature embryos of white clover (Trifolium repens L.) cv. Osceola were exposed to 2,4-D or NAA to induce somatic embryogenesis. NAA at 10 or 20 mg 1–1 was very inefficient at stimulating embryogenesis, while concentrations of 30 or 40 mg 1–1 resulted in death of the explant tissue. Continuous exposure of cotyledons to 40 mg 1–1 2,4-D resulted in somatic embryos which were arrested at the globular stage, or which underwent cycles of secondary embryogenesis, never proceeding beyond the globular stage. A 10 day exposure time to 2,4-D at the same concentration led to formation of somatic embryos, most of which had poorly developed cotyledons. Almost 10% of the somatic embryos converted into plants following transfer to medium devoid of growth regulators. Attempts to improve morphology of somatic embryos by using shorter exposure times to 2,4-D at 40 mg 1–1, or by maintaining the 10 day exposure time while varying the concentration of 2,4-D, were not successful. Plants were obtained from all parents evaluated, although at different frequencies. 相似文献
11.
J. J. Rybczyński W. Zduńczyk 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,73(2):267-271
Summary A tissue culture of five wild species of the Secale genus, i.e., S. africanum (Stapf.), S. ancestrale (Zhuk.), S. kuprianovii (Grossh), S. segetale (Rosher.), and S. vavilovii (Grossh), from immature embryos of sizes (stages) varying between 1.0 mm to 3.0mm, cultured on MS (1962) mineral nutrient medium supplemented with 0.62 mg/1–5.0 mg/1 of 2,4-D, was established. Initially various types of callus were observed and a correlation between genotype, size of explant and 2,4-D concentration was found. The best embryogenic response was observed when explants were smaller than 1.0 mm. Induction of somatic embryogenesis of 2.0 mm–3.0 mm explants required a higher concentration of 2,4-D. Most embryoids were formed in the presence of 5.0 mg/l of 2,4-D. Secale africanum and S. kuprianovii appeared to have the highest embryogenic capacity among the five investigated species. For embryoids germination to plantlets the MS medium supplemented with GA3 and cytokinins was used. Ultimately, out of the 932 regenerants obtained 364 originated from somatic embryogenesis.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- GA3
deGibberellic acid
- BAP
Benzylaminopurine 相似文献
12.
P. Jha C. B. Yadav V. Anjaiah V. Bhat 《In vitro cellular & developmental biology. Plant》2009,45(2):145-154
An efficient in vitro plant regeneration protocol through somatic embryogenesis and direct shoot organogenesis has been developed for pearl millet
(Pennisetum glaucum). Efficient plant regeneration is a prerequisite for a complete genetic transformation protocol. Shoot tips, immature inflorescences,
and seeds of two genotypes (843B and 7042-DMR) of pearl millet formed callus when cultured on Murashige and Skoog (MS) medium
supplemented with varying levels of 2,4-dichlorophenoxyacetic acid (2,4-D; 4.5, 9, 13.5, and 18 μM). The level of 2,4-D, the
type of explant, and the genotype significantly effected callus induction. Calli from each of the three explant types developed
somatic embryos on MS medium containing 2.22 μM 6-benzyladenine (BA) and either 1.13, 2.25, or 4.5 μM of 2,4-D. Somatic embryos
developed from all three explants and generated shoots on MS medium containing high levels of BA (4.4, 8.8, or 13.2 μM) combined
with 0.56 μM 2,4-D. The calli from the immature inflorescences exhibited the highest percentage of somatic embryogenesis and
shoot regeneration. Moreover, these calli yielded the maximum number of differentiated shoots per callus. An efficient and
direct shoot organogenesis protocol, without a visible, intervening callus stage, was successfully developed from shoot tip
explants of both genotypes of pearl millet. Multiple shoots were induced on MS medium containing either BA or kinetin (4.4,
8.8, 17.6, or 26.4 μM). The number of shoots formed per shoot tip was significantly influenced by the level of cytokinin (BA/kinetin)
and genotype. Maximum rooting was induced in 1/2 strength MS with 0.8% activated charcoal. The regenerated plants were transferred
to soil in pots, where they exhibited normal growth. 相似文献
13.
Summary
In vitro propagation of Andrographis paniculata (Burm. f.) Wallich ex Nees through somatic embryogenesis, and influence of 2,4-dichlorophenoxyacetic acid (2,4-1) on induction, maturation, and
conversion of somatic embryos were investigated. The concentration of 2,4-D in callus induction medium determined the induction,
efficacy of somatic embryogenesis, embryo maturation, and conversion. Friable callus initiated from leaf and internode explants
grown on Murashige and Skoog (MS) medium supplemented with 2.26, 4.52, 6.78, and 9.05μM 2,4-D started to form embryos at 135, 105, 150, and 185d, respectively, after explant establishment. Callus initiated at
13.56μM 2,4-D did not induce embryos even after 240 d, whereas those initiated on MS medium with 4.52μM 2,4-D was most favorable for the formation and maturation of somatic embryos. Callus subcultured on the medium with reduced
concentration of 2,4-D (2.26μM) became embryogenic. This embryogenic callus gave rise to the highest number of embryos (mean of 312 embryos) after being
transferred to half-strength MS basal liquid medium. The embryos were grown only up to the torpedo stage. A higher frequency
of embryos developed from callus initiated on 2.26 or 4.52 μM 2,4-D underwent maturation compared to that initiated on higher concentrations of 2.4-D. The addition of 11.7μM silver nitrate to half-strength MS liquid medium resulted in 71% of embryos undergoing maturation, while 83% of embryos developed
into plantlets after being transferred to agar inedium with 0.44 μMN6-benzyladenine and 1.44 μM gibberellic acid. Most plantlets (88%) survived under field conditions and were morphologically identical to the parent plant. 相似文献
14.
Summary
Baloskion tetraphyllum is a member of the Restionaceae and is an important species for the rehabilitation of disused mine sites and wetland areas, and is also highly prized as
a cut flower. Its use for restoration of disturbed land is, however, severely limited, due to very poor propagation success
by conventional methods. A study was conducted to evaluate the potential of somatic embryogenesis for the large-scale propagation
of this species. A variety of auxins (at different concentrations) were investigated for their efficacy in stimulating somatic
embryogenesis. Somatic embryos were successfully induced from excised coleoptiles of B. tetraphyllum on half-strength Murashige and Skoog (1/2MS) medium supplemented with 1 μM 2,4-dichlorophenoxyacetic (2,4-D). To scale up the production, proliferation of secondary somatic embryos was achieved using
primary somatic embryos as the tissue source, on 1/2MS+1 μM 2,4-D resulting in a 30-fold increase in somatic embryo, numbers. Almost all the somatic embryos developed into plants and
were established ex vitro. The other auxins investigated, including p-chlorophenoxyacetic acid, indole-3-acetic acid, α-naphthaleneacetic acid, and picloram, were not as effective as 2,4-D. The
age, of the explant material significantly influenced somatic embryogenesis with white, young coleoptiles (5–7 d) producing
50% more somatic embryos than green, more mature (8–14 d) coleoptiles. The protocol developed for B. tetraphyllum has the potential to be commercially viable, with an estimated 22 000 somatic embryos produced from 1 g of plant material.
This research may also have a positive impact on the propagation of other important Restionaceae species. 相似文献
15.
Summary In order to establish a protocol for somatic embryogenesis of annatto, Bixa orellana L., seeds (70 d after anthesis) from field-grown orchards had their coats dissected off, and immature zygotic embryos were
excised aseptically from immature seeds collected from field-grown trees and used as explants. Embryos were cultured onto
MS medium supplemented with or without different combinations of plant growth regulators and activated charcoal. Direct somatic
embryogenesis was induced on explants incubated either in Murashige and Skoog (MS), 2,4-dichlorophenoxyacetic acid (2,4-D),
and/or kinetin-supplemented media after 25 d of culture. The highest frequencies of embryogenesis and embryos per explant
were obtained on medium containing 2.26 μM 2.4-D, 4.52μM kinetin, and 1.0 gl−1 activated charcoal. The presence of charcoal was critical in increasing embryos per explant, to reduce the time to obtain
somatic embryos, and mainly to prevent callus proliferation and subsequent indirect somatic embryogenesis. No embryogenic
response was achieved when mature embryos were used. It was also observed that embryogenic response was significantly affected
by genotype. Histological investigations revealed that primary direct somatic embryos differentiated exclusively from the
protodermis or together with the outer ground meristem cell layers of the zygotic embryo axis, and from the protodermis of
zygotic cotyledons. Diverse morphological differences, including malformed embryos, were observed among somatic embryos. In
spite of the high frequencies of histodifferentiation of all embryo stages, a very low conversion frequency to normal plants
from somatic embryos was observed. 相似文献
16.
17.
Piedad Gallego Oscar Hita Nieves Villalobos Ana Dorado Luisa Martin Hilario Guerra 《In vitro cellular & developmental biology. Plant》2001,37(2):199-203
Summary An efficient plant regeneration system employing cotyledons, hypocotyls, petioles and leaves as explants and characterized
by continuous and prolific production of somatic embryos, has been developed with Medicago arborea ssp. arborea. The optimal somatic embryogenic response was obtained using a two-step protocol, where explants were incubated under a 16
h photoperiod for 2 mo. on Murashige and Skoog (MS) medium containing 2,4-dichlorophenoxyacetic acid (2,4-D; 9 μM) and kinetin (9 μM), and followed by transfer to kinetin-free MS medium with 2,4-D (2.25 μM). Removal of the cytokinin and a reduction in the concentration of auxin (2.25 μM) in the second step of culture were critical for enhanced production of somatic embryos. The best explants proved to be cotyledons
and petioles (i.e. a mean of 18.0±0.70 somatic embryos at 3 mo. for petiole culture). Somatic embryos were converted into
normal plantlets (8.0±0.89%) when cultured on basal MS medium with 5 μM indolebutyric acid. No somatic embryos were obtained when thidiazuron was used in the culture media. Using petioles as explants
and N6-benzyladenine (BA), embryogenesis was induced in the second step of culture when BA was removed from the medium and the concentration
of 2,4-D was decreased to 2.25 μM. 相似文献
18.
Somatic embryogenesis and plant regeneration of Canada wildrye (Elymus canadensis L.) from tissue culture was investigated by culturing immature embryos and inflorescences on MS medium containing 2 mg/l 2,4-D. The optimum size of explants for maximum embryogenic callus formation was 1.0 to 1.5 mm for embryos and 4 to 6 cm for inflorescences. Plant regeneration from the subcultured embryogenic callus was attempted monthly using hormone-free MS medium or MS medium with 0.5 mg/1 2,4-D and 0.3 mg/l GA3. Three hundred and fifty seven plantlets were regenerated from the callus cultures of both explant sources during a six month period. Ten chlorophyll deficient plants accounting for 2.8% of the total regenerants were observed. One plant with white striped leaves survived and was found to be an octoploid.Abbreviations GA3
gibberellic acid
- MS
Murashige and Skoog (1962)
- 2,4-D
2,4-dichlorophenoxyacetic acid 相似文献
19.
Zhiyong Pan Shiping Zhu Rui Guan Xiuxin Deng 《Plant Cell, Tissue and Organ Culture》2010,103(2):145-153
The compound 2,4-Dicholorophenoxyacetic acid (2,4-D) is an important growth regulator which is used in the majority of embryogenic
cell and tissue culture systems. However, 2,4-D also appears to have a negative effect on growth and development of plant
tissues and organs cultured in vitro. For example, 2,4-D exerts inhibition on in vitro somatic embryo initiation and/or development
of most citrus species. To understand the molecular mechanism by which 2,4-D inhibits somatic embryogenesis (SE), proteomic
changes of Valencia sweet orange (Citrus sinensis) embryogenic callus induced by treatments with a high concentration of 2,4-D (6 mg l−1) was investigated. Nine 2,4-D-responsive proteins were identified, of which eight were up-regulated and one was down-regulated.
Interestingly, three of the eight up-regulated proteins were osmotic stress-associated, suggesting that 2,4-D induced osmotic
stress in Valencia embryogenic callus. This speculation was supported by results from our physiological studies: 2,4-D treated
callus cells exhibited increased cytoplasm concentration with a significant reduction in relative water content (RWC) and
an obvious increase in levels of two osmolytes (proline and soluble sugar). Taken together, our results suggested that 2,4-D
could inhibit somatic embryo initiation by, at least in part, inducing osmotic stress to citrus callus cells. 相似文献
20.
An efficient protocol was developed for in vitro plant regeneration via somatic embryogenesis from cell suspension cultures
of metal tolerant grass Echinochloa colona (L.) Link. Callus was obtained by culturing leaf base on MS medium supplemented
with 0.5 mg dm-3 of 6-benzylaminopurine (BAP) and 2.0 mg dm-3 of 1-naphthaleneacetic acid (NAA). Cell suspensions were initiated and established in MS liquid medium containing 0.5 mg
dm-3 BAP, 1.0 mg dm-3 NAA and 2.0 mg dm-3 2,4-dichlorophenoxyacetic acid (2,4-D). A reduction in the concentration of 2,4-D to 0.5 mg dm-3 induced formation of somatic embryos. The embryos developed and grew into normal plants in the presence of half strength
MS medium without growth regulators. The regenerated plants were hardened in the greenhouse and subsequently grown in the
open. This system may be also used for isolation and culture of protoplasts as a first step in somatic hybridization.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献