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1.
Guillermo Pérez Andrew Mbogholi Fernando Sagarra Carlos Aragón Justo González Miriam Isidrón José Carlos Lorenzo 《In vitro cellular & developmental biology. Plant》2011,47(3):428-433
We previously reported a partial agricultural and amplified fragment length polymorphism (AFLP) characterization of two new
pineapple somaclones (P3R5 and Dwarf) derived from in vitro culture of the donor cv. Red Spanish Pinar. Both somaclonal variants showed different AFLP banding patterns compared to the
donor cultivar, although they were separated by less than 0.09 U of genetic distance. The present report shows data of various
indicators of morphology and physiology of P3R5 and Dwarf D leaves. The stoma diameter, number of stomata per square millimiter, diameter of leaf vascular tissue, thickness of the leaf
aquiferous parenchyma, and thickness of the leaf photosynthetic parenchyma were measured. The photosynthetic rate, the transpiration
rate, the water use efficiency, the internal leaf CO2 concentration, and the chlorophyll pigment contents were recorded as well. Between the somaclonal variant P3R5 and the donor
genotype, statistically significant differences were recorded in all indicators with the exception of the stoma diameter and
the photosynthetic rate. Comparing the somaclonal variant Dwarf and the cv. Red Spanish Pinar (donor), statistically significant
differences were also recorded in all parameters except in the stoma diameter and in the transpiration rate. This investigation
was performed to demonstrate that small changes in the pineapple DNA may result in relevant phenotypic modifications. 相似文献
2.
Xiuli Shen Jianjun Chen Michael E. Kane Richard J. Henny 《Plant Cell, Tissue and Organ Culture》2007,91(1):21-27
The occurrence of somaclonal variation among regenerants derived through indirect shoot organogenesis from leaf explants of
three Dieffenbachia cultivars Camouflage, Camille and Star Bright was evaluated. Three types of somaclonal variants (SV1, SV2, and SV3) were
identified from regenerated plants of cv. Camouflage, one type from cv. Camille, but none from cv. Star Bright. The three
variants had novel and distinct foliar variegation patterns compared to cv. Camouflage parental plants. Additionally, SV1
was taller with a larger canopy and longer leaves than parental plants and SV2. SV2 and SV3 did not produce basal shoots (single
stem) but basal shoot numbers between SV1 and parental plants were similar ranging from three to four. The variant type identified
from regenerated cv. Camille had lanceolate leaves compared to the oblong leaves of the parent. This variant type also grew
taller and had a larger canopy than parental plants. The rates of somaclonal variation were up to 40.4% among regenerated
cv. Camouflage plants and 2.6% for regenerated cv. Camille. The duration of callus culture had no effect on somaclonal variation
rates of cv. Camouflage as the rates between plants regenerated from 8 months to 16 months of callus culture were similar.
The phenotypes of the identified variants were stable as verified by their progenies after cutting propagation. This study
demonstrated the potential for new cultivar development by selecting callus-derived somaclonal variants of Dieffenbachia. 相似文献
3.
4.
Daviel Gómez Lázaro Hernández Bárbara Valle Julia Martínez Mariela Cid Maritza Escalona Martha Hernández Gerrit T. S. Beemster Christoph C. Tebbe Lourdes Yabor José Carlos Lorenzo 《Acta Physiologiae Plantarum》2017,39(12):277
Effects of salinity (NaCl) and the carbon source mannitol (0–200 mM) on micropropagation of pineapple cv. MD2 were analyzed in temporary immersion bioreactors (TIBs). Shoot multiplication rate, shoot cluster fresh weight and levels of aldehydes, chlorophylls, carotenoids and phenolics were determined in the plant material. The content of soluble phenolics in the culture medium was also evaluated. NaCl or mannitol above concentrations of 50 mM decreased pineapple shoot multiplication and fresh weight significantly. Two hundred mM NaCl decreased multiplication rate by 71.5% and cluster fresh weight by 40.0%. NaCl increased 2.4 times the levels of other aldehydes; 1.4 times the soluble phenolics in shoots; and 1.4 times the phenolics excreted to the culture medium. On the other hand, mannitol decreased the multiplication rate and cluster fresh weight by about 60%. Mannitol increased the contents of chlorophyll b 1.4 times and soluble phenolics 2.1 times. Results indicated that pineapple cv. MD2 is more sensitive to NaCl than to mannitol. Multiplication rates indicate that a 50% reduction was obtained with 37.4 mM NaCl and 66.5 mM mannitol. These concentrations can be used to stress shoots during micropropagation in TIBs and screen for/detect somaclonal variants with an increased salinity or drought tolerance. 相似文献
5.
T. Cai G. Ejeta J. D. Axtell L. G. Butler 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1990,79(6):737-747
Summary Genetic variants were found among over 6,000 primary plants (R1) regenerated from embryogenic tissue cultures of eight high tannin sorghums [Sorghum bicolor (L.) Moench]. Field assessment of somaclonal variation has progressed to the R2 population, with over 48,000 R2 seedlings (27,000 plants) in 1,126 rows from 1,055 R1 plants. A total of 43 variant phenotypes was recovered, including several types of chlorophyll deficiencies, dwarfism, short culm, sterility, narrow leaf, and several previously unreported variants, such as ragged leaf, multibranched heads, and Hydra, a developmental variant which produces large numbers of panicles. Variation production greatly depends on parent genotype and appears to increase with increasing time in cultures. The toal average somaclonal variation rate (based per 100 R1 plants) and somaclonal variant frequency (based per 100 R2 plants) estimated in the tested population were 11.3 and 1.6, respectively. Chimerism was found in regenerants. The estimated size of the mutated sector carried by mutant regenerants ranged from the whole plant to less than 3% of a single head. The average proportion of mutated R1 heads carrying large (80%–100%), medium (40%–80%), and small (<40%) mutated sectors was 38.7%, 26.0% and 35.3%, respectively. Some sector mutations do not appear until the R3 generation. In order to avoid losing variants, the population for selecting somaclonal variation should be as large as possible. Some of these variants found may be useful for further study or for use in breeding programs. 相似文献
6.
B. Wang D. X. Peng Z. X. Sun N. Zhang S. M. Gao 《In vitro cellular & developmental biology. Plant》2008,44(2):105-111
Ramie [Boehmeria nivea (L.) Gaud] is one of the most important perennial fiber crops in China. In vitro tissue culture of ramie could serve as an important means for its improvement through genetic transformation. To improve
the regeneration capacity of ramie, the effects on plant regeneration of donor plant age, basal medium, plant growth regulators,
and culture conditions were evaluated using explants derived from the cotyledon, hypocotyl, leaf, petiole, and stem of ramie
seedlings. Cotyledons and hypocotyls excised from 4-d-old seedlings and leaves and petioles and stems from 15-d-old seedlings
were optimal explants. The highest regeneration efficiency was obtained on Murashige and Skoog salts with Gamborg’s B5 vitamins basal medium containing 2.27 μM thidiazuron (TDZ) and 0.054 μM naphthaleneacetic acid (NAA) for the five explant
types tested. A photoperiod of 16:8 h (light/dark) was found to be superior than continuous darkness for regeneration of ramie
using TDZ. The regenerated shoots were transferred to hormone-free medium for shoot elongation and successfully rooted on
half-strength Murashige and Skoog supplemented with 0.134 μM NAA. The rooted plantlets with four to five leaves were transplanted
to greenhouse for further growth. 相似文献
7.
Yuehua Sun Yanling Zhao Xiaojuan Wang Guirong Qiao Guoliang Chen Ye Yang Jing Zhou Liang Jin Renying Zhuo 《Acta Physiologiae Plantarum》2009,31(1):33-41
The aim of this work is to develop a method of plant regeneration from leaf explants of Platanus occidentalis L. successfully. Woody plant medium (HortScience 16:453–459, 1981) and Murashige and Skoog (Physiol Plant 15:473–497, 1962)
medium were used as induced and rooted basal medium, respectively. The effects of combinations of 6-BA, IBA, NAA and KT with
different concentrations on adventitious bud regeneration from P. occidentalis leaf explants were compared. The results showed that the highest shoot regeneration frequency (90%) and maximum number (13.72 ± 0.44)
of shoots per explant was recorded on WPM medium supplemented with 22.20 mmol l−1 6-BA and 0.49 mmol l−1 IBA. A 40-day-old explants were much more productive for shoot formation than others in this study. The regenerated shoots
were cultured on MS medium supplemented with 1.33 mmol l−1 6-BA, 0.16 mmol l−1 NAA and 2% (w/v) adenine, after 2-week shoots were transferred to 1/2 MS medium supplemented with 0.49 mmol l−1 IBA for rooting. Hardened plantlets via acclimatization were transferred to pots and transplanted to the soil finally. To
ascertain whether tissue culture had effects on the genetic stability of plantlets regenerated, the genetic diversity was
assessed using RAPD marker. A total of 96 bands ranging from 0.5 to 2.2 kb with an average of 6.4 bands per primer, were obtained
using 15 primers. Amplified products exhibited few of polymorphic patterns across all the plants of P. occidentalis and the overall frequency of detection of somaclonal polymorphisms was lower than 0.0104%.
Yuehua Sun, Yanling Zhao, and Xiaojuan Wang contributed equally to this work. 相似文献
8.
S. C. Debnath 《In vitro cellular & developmental biology. Plant》2009,45(2):122-128
An efficient system to regenerate shoots on excised leaves of greenhouse-grown wild lowbush blueberry (Vaccinium angustifolium Ait.) was developed in vitro. The effect of thidiazuron (TDZ) on adventitious bud and shoot formation from apical, medial, and basal segments of the leaves
was tested. Leaf cultures produced multiple buds and shoots with or without an intermediary callus phase on 2.3–4.5 μM TDZ
within 6 wk of culture initiation. The greatest shoot regeneration came from young expanding basal leaf segments positioned
with the adaxial side touching the culture medium and maintained for 2 wk in darkness. Callus development and shoot regeneration
depended not only on the polarity of the explants but also on the genotype of the clone that supplied the explant material.
TDZ-initiated cultures were transferred to medium containing 2.3–4.6 μM zeatin and produced usable shoots after one additional
subculture. Elongated shoots were dipped in 39.4 mM indole-3-butyric acid powder and planted on a peat:perlite soilless medium
at a ratio of 3:2 (v/v), which yielded an 80–90% rooting efficiency. The plantlets were acclimatized and eventually established in the greenhouse
with 75–85% survival. 相似文献
9.
Chun-Miao Feng Rongda Qu Li-Li Zhou De-Yu Xie Qiu-Yun Xiang 《Plant Cell, Tissue and Organ Culture》2009,97(1):27-37
Dwarf dogwoods (or the bunchberries) are the only suffrutex in Cornaceae. They are attractive ground cover ornamentals with clusters of small flowers surrounded by petaloid bracts. Little has been
reported on plant regeneration of dogwoods. As a step toward unraveling the molecular basis of inflorescence evolution in
Cornus, we report an efficient regeneration system for a dwarf dogwood species C. canadensis through organogenesis from rejuvenated leaves, and characterize the development of the plantlets. We used the nodal stem
segments of vegetative branches as explants. Micropropogated shoots were quickly induced from axillary buds of nodes on an
induction medium consisting of basal MS medium supplemented with 4.44 μM BAP and 0.54 μM NAA. The new leaves of adventitious
shoots were used as explants to induce calli on the same induction medium. Nearly 65% of leaf explants produced calli, 80%
of which formed adventitious buds. Gibberellic acid (1.45 μM) added to the same induction medium efficiently promoted quick
elongation of most adventitious buds, and 0.49 μM IBA added to the basal MS medium promoted root formation from nearly 50%
of the elongated shoots. The growth of plantlets in pot soil was characterized by the development of functional woody rhizomes,
which continuously developed new aboveground vegetative branches, but not flowering branches, within the past 12 months. Potential
reasons causing the delay of flowering of the regenerated plants are discussed. The establishment of this regeneration system
facilitates developing a genetic transformation system to test candidate genes involved in the developmental divergence of
inflorescences in Cornus.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
M. J. Prado M. V. Gonzalez S. Romo M. T. Herrera 《Plant Cell, Tissue and Organ Culture》2007,88(1):1-10
The present work reports on a study of plant regeneration carried out with callus from the leaf blades and petioles of field-grown
male adult kiwifruit plants (Actinidia deliciosa (Chev.) Liang and Ferguson). The cultivars used were ‘Tomuri’ and clone A, a selected male plant grown in north western Spain.
The best shoot induction conditions were obtained in ‘Tomuri’ leaf blades cultured in K(h) medium in the presence of 23 μM
Zeatin and 0.1 μM NAA. Under these conditions, more than 80% of organogenic callus induction was observed, with an average
of 14 new shoots in the second subculture. The initial length of the shoots affected shoot elongation, which was accomplished
by culturing isolated shoots in K(h) medium with half-strength salts, supplemented with 0.4 μM Zeatin and 0.1 μM NAA. A possible
detrimental long-term effect of cytokinins on shoot elongation can account for the results, since elongation was not observed
until 1 month of culture in elongation medium. For rooting, shoots (1 cm in length) were basally immersed in a 5 mM IBA solution
for 15 s, and transferred to half-strength K(h) basal medium. Regenerated plants were acclimated in a sterile peat:perlite
substrate for 10 days, and then transferred to soil. AFLP analysis was accomplished with 15 primer combinations from which
13 showed reproducible and well-resolved bands, producing a total of 1321 fragments from which 1281 were polymorphic (97%).
A dendrogram was constructed using both monomorphic and polymorphic bands, showing genetic variation among field-grown plants
and tissue culture-derived regenerants. 相似文献
11.
A regeneration system was developed for oriental lily (Lilium orientalis) based on both leaf and bulb scale. Adventitious shoots were regenerated from leaves of in vitro cultures on Murashige and Skoog medium containing thidiazuron (TDZ) or 6-benzylaminopurine (BA) and naphthaleneacetic acid
(NAA). The highest percent regeneration from leaf explants was 74.2%, being observed on medium containing 10.8 μM TDZ and
0.54 μM NAA. The highest mean number of shoots generated was 4.4 and was obtained from bulb scale explants on medium containing
0.54 μM TDZ and 0.54 μM NAA. Adventitious shoots were successfully rooted at rates ranging from 79.2% to 100%. The rooted
plantlets survived after acclimatization in the greenhouse. The effect of kanamycin concentration on adventitious shoot regeneration
was also evaluated, a value of 100 mg l−1 being suggested as a lethal dose for lily transformation. Eighteen ISSR markers were employed to determine the genetic stability
of the regenerated shoots in comparison to their mother plant. Eleven primers in total produced 70 clear and reproducible
bands. Genetic similarity indicators among the clonal derivatives and the mother plant ranged from 0.92 to 1.0. All 15 micropropagated
progenies and the mother plant could be grouped together in one major cluster with a similarity level of 92%. The somaclonal
variation rate across the plantlets was estimated as 4.2%, indicating that direct shoot formation from explant regeneration
is a safe method for multiplication of “true-to-type” plants. 相似文献
12.
Sheila Jazmín Reyes-Zambrano Carlos Alberto Lecona-Guzmán Federico Antonio Gutiérrez-Miceli Víctor Manuel Ruiz-Valdiviezo Arely Anayansi Vargas-Díaz 《Phyton》2021,90(6):1727-1739
Agave americana L. callus were exposed to different concentrations of ethyl methanesulphonate (EMS) 0, 15, 30, 45 and 60 mM and to different times of exposure (2 and 4 h). The viability and capacity of shoot formation were shown to be affected when the callus were exposed to high concentrations (30–60 mM). Only the callus exposed to 15 mM EMS presented shoot formation; the exposure time of two hours produced the largest quantity of shoots regenerated per callus (21 shoots/callus). In order to generate somaclonal variants resistant to Fusarium oxysporum, a selection pressure was applied through of a culture filtrate (CF) of 100 ppm of the fungus. This was made in callus obtained in the treatment with 15 mM EMS during 2 h of exposure. The CF caused oxidation and necrosis in 71.25% of the callus; however, they were capable of generating shoots (3.5 shoots/callus). Molecular markers type RAPD, ISSR and DAMD were used to evaluate the genetic variation arising from the mutations caused by EMS on control plants and 16-month-old somaclonal variants. The polymorphic information content (PIC) for each one of the initiating groups was: 0.28 (DAMD), 0.09 (ISSR) and 0.14 (RAPD). DAMD revealed a greater percentage of polymorphism than RAPD and ISSR. Polymorphic bands were detected in the somaclonal variants. This indicated that the EMS caused genetic variation in the regenerated plants conferring resistance to them against Fusarium oxysporum. 相似文献
13.
An efficient method of micropropagation for Eclipta alba from young nodal axils of shoot tip explants has been developed by giving special attention to ‘priming’ in vitro plantlets
in view of increasing their hardening ability after transplantation ex vitro. Among 3 cytokinins—BAP, kinetin and TDZ, BAP
was found most effective in inducing and proliferating adventitious shoots. The highest frequency of responding explants (100%)
and maximum number of shoots (23.0) per explant were obtained after 60 days culture on MS medium containing 8.8 μM BAP. Cent
percent shoots developed roots directly from shoot base when transferred to growth regulator-free MS medium. For priming E. alba microshoots, 6.3 μM of chlorocholine chloride (CCC) was found most effective. The major changes observed in 30 days old treated
shoots were, production of increased number of root, elevation of chlorophyll level in leaves and increase in plant biomass.
Furthermore, arrested undesirable shoot elongation made the plants sturdier and more suitable for acclimatization. The primed
micropropagated E. alba plants were healthy and survived by higher frequency (100%) in soil in comparison to the non-treated plants (84% survival). 相似文献
14.
Summary A procedure for plant regeneration, flower and plant formation from petiolar and inflorescence nodal explants of culantro
is discribed. Leaf petioles were excised from young leaves of non-flowering plants while nodal explants were excised from
the inflorescence. Explants were cultured in Murashige and Skoog (MS) medium alone or supplemented with 0.5μM naphthaleneacetic acid (NAA) and 0.9, 1.8, 4.5, or 9 μM thidiazuron (TDZ). All explants produced multiple shoots. In addition, nodal explants formed flowers. Shoot number, flower
number and shoot length were influenced by TDZ and NAA. Rooted shoots from both types of explants were transferred to soil
where plants were successfully established. 相似文献
15.
16.
Arzu Ucar Turker Esra Cansever Mutlu Arzu Birinci Yıldırım 《Acta Physiologiae Plantarum》2008,30(4):421-426
Epilobium angustifolium L. (fireweed) is a medicinal plant that has been used to treat diarrhea, mucous colitis, irritable-bowel syndrome, skin problems,
prostate problems, menstrual disorders, asthma, whooping cough, and hiccups. A highly efficient and rapid regeneration system
via multiple shoot formation was developed for fireweed. Explants (leaf, petiole, root, and stem segments) excised from sterile
seedlings were cultured on medium supplemented with different concentrations and combinations of various plant growth regulators.
Explant browning, a major problem for regeneration, was overcome by adding 100 mg/l ascorbic acid to all prepared media containing
growth regulator combinations. Root explants formed more shoots than other explants. Best shoot proliferation was obtained
from root explants cultured on media with 0.1 mg/l BA and 0.5 mg/l IAA. Regenerated shoots were transferred to rooting media
containing different concentrations of IAA, IBA, NAA or 2,4-D. Most shoots developed roots on medium with 0.5 mg/l IAA. Rooted
explants were transferred to vermiculate in Magenta containers for acclimatization and after 3 weeks they were planted in
to plastic pots containing potting soil and maintained in the plant growth room. 相似文献
17.
Shaoyun Lu Chuanhao Chen Zhongcheng Wang Zhenfei Guo Haihang Li 《Plant cell reports》2009,28(3):517-526
Eight somaclonal variants with enhanced drought tolerance were isolated from regenerated plants of triploid bermudagrass (Cynodon dactylon × Cynodon transvaalensis cv., TifEagle). Three of them (10-17, 89-02, 117-08) with strong drought tolerance were selected for investigations of physiological
responses to drought stress. Compared to the parent control, TifEagle, the somaclonal variants had higher relative water contents
and relative growth, and lower ion leakages in the greenhouse tests, while no difference in evapotranspirational water losses
and soil water contents was observed between the variants and TifEagle. The variants also had less leaf firing in the field
tests under drought stress. Superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities decreased
gradually in responses to drought stress in all plants and exhibited negative correlations with ion leakage, indicating that
the declined activities of these antioxidant enzymes were associated with drought injury in the triploid bermudagrass. However,
CAT activities were significantly higher in all three variants than in TifEagle during drought stress. Two variants, 10-17
and 89-02, also had significantly higher APX activities than TifEagle before and during the first 4 days of drought treatments.
These two lines also showed higher SOD activities after prolonged drought stress. Proline, total soluble sugars and sucrose
were accumulated under drought stress in all plants and exhibited positive correlations with ion leakage. More proline and
sugars were accumulated in TifEagle than in the variants. The results indicated that higher activities of the antioxidant
enzymes in the variants during drought stress are associated with their increased drought tolerance. 相似文献
18.
在1/3海水培养基上筛选豆瓣菜耐盐变异体 总被引:1,自引:0,他引:1
The responses of stem segments of watercress ( Nasturtium offtcinale R. Br. ) to 6-BA, NAA and 2,4-D were studied. MS medium supplemented with 2.0 mg/L 6-BA, 0.2 mg/L 2,4-D was used for callus initiation and maintainance. MS medium supplemented with 4.0 mg/L 6-BA was suitable for plant regeneration and MS medium without plant hormone supplement was used for rooting and plant propagation. For screening of salt. tolerant calli, stem segments of watercress were plated onto callus initiation medium containing 1/3 natural seawater. Seventeen out of the 325 plated explants produced calli. The growth curves demonstrated that the growth rate of salt-tolerant calli on saline medium almost matched that of the control calli on normal medium. Some of the salt-tolerant calli were transferred to the normal regeneration medium or saline regeneration medium to induce plant regeneration. In the first case, buds and shoots were regenerated in the same way as those of control calli on normal regeneration medium. More than 1 000 regenerated shoots were obtained of which 83 regenerated shoots were cut and transferred to saline MS base medium. At first, all shoot growth was inhibited, but 40 days after the transfer, rapid-growing axillary shoots were observed on 16 of the original shoots but none on the control shoots on saline MS base medium. Moreover, green spots appeared on most calli 10 days after they were transferred to saline medium, however buds appeared only on 5 calli from the 30 transferred calli and at the end only 2 rapid-growing shoots were obtained from two calli. In total, 18 variant lines were obtained through propagation of the salt-tolerant shoots on saline MS base medium. RAPD analysis was performed in 10 of the 18 salt-tolerant variant lines and DNA variation was detected in all the tested variant lines. 相似文献
19.
Raya Liberman Liat Shahar Ada Nissim-Levi Dalia Evenor Moshe Reuveni Michal Oren-Shamir 《Plant Cell, Tissue and Organ Culture》2010,100(3):345-348
A protocol for plantlet regeneration through shoot formation was developed for the neotropical shrub Brunfelsia calycina. This shrub is unique in its change in flower color from dark purple to white. Explants from young and mature leaves were
incubated on MS medium (pH 5.7, 30 g/l sucrose, 7.5 g/l agar) with various combinations of Indole-3-acetic acid (IAA) and
6-Benzyladenine (BA) under a 16 h photoperiod at a constant temperature of 25°C. Shoot emergence was best at 4.44 μM BA and
2.85 μM IAA for young leaf explants, and at 8.88 μM BA, 2.85 μM IAA for mature leaf explants. When shoots were transferred
to MS medium supplemented with 1.23–2.46 μM indole butrytic acid (IBA), they developed roots. 相似文献
20.
Studies on somaclonal variation in Phalaenopsis 总被引:6,自引:0,他引:6
The morphological and genetic variations in somaclones of Phalaenopsis True Lady “B79-19” derived from tissue culture were evaluated. In 1360 flowering somaclones, no apparent difference was found
in the shape of the leaves, whereas flowers in some somaclones were deformed. We have demonstrated that 38 selected random
primers can be used to generate amplified segments of genomic DNA and to differentiate polymorphisms of somaclonal variations
in Phalaenopsis. The random amplified polymorphic DNA (RAPD) data indicated that normal and variant somaclones are not genetically identical.
We also studied the banding patterns of aspartate aminotransferase (AAT) and phosphoglucomutase (PGM) in young leaves of variant
and normal somaclones of Phalaenopsis. With respect to AAT, three distinct banding patterns were found in normal somaclones and only two-banded phenotypes were
detected in variant somaclones. In a comparison of the banding patterns of PGM isozymes, three to four bands were detected
in normal somaclones and two to three bands in variant ones.
Received: 15 August 1997 / Revision received: 16 February 1998 / Accepted: 1 May 1998 相似文献