Efficacious somatic embryogenesis and fertile plant recovery from shoot apex explants of onion (Allium cepa. L.)

An efficient somatic embryogenesis and regeneration system was developed for the first time in onion using shoot apex explants. These explants were used to initiate callus in Murashige and Skoog (MS) medium supplemented with 4.0 mg l^?1 2,4-dichlorophenoxyacetic acid. The induction frequency of primary callus in this medium was 85.3%. The primary calli were then transferred onto medium supplemented with 2.0 mg l^?1 2,4-dichlorophenoxyacetic acid. Following two biweekly subcultures, embryogenic callus formed. Inclusion of a low concentration of 6-benzylaminopurine in the subculture medium promoted the formation of embryogenic callus. The addition of 2.0 mg l^?1 glycine, 690 mg l^?1 proline, and 1.0 g l^?1 casein hydrolysate also increased the frequency of callus induction and embryogenic callus formation. The highest frequency of embryogenic callus (86.9%) and greatest number of somatic embryos (26.3 per callus) were obtained by the further addition of 8.0 mg l^?1 silver nitrate. Somatic embryos formed plantlets on regeneration medium supplemented with 1.5 mg l^?1 6-benzylaminopurine; addition of 2.0 mg l^?1 glycine to the regeneration medium promoted a high frequency of regeneration (78.1%) and plantlet formation (28.7 plants per callus). The regenerated plantlets were transferred to half-strength MS medium supplemented with 1.5 mg l^?1 indole-3-butyric acid for root development; the maximum frequency of root formation was 87.7% and the average number of roots was 7.6 per shoot. The regenerated plantlets were successfully grown to maturity after hardening in the soil. This is the first report of somatic embryogenesis and regeneration from shoot apex explants of onion.     

<Emphasis Type="Italic">In vitro</Emphasis> propagation of an endangered plant species, <Emphasis Type="Italic">Thermopsis turcica</Emphasis> (Fabaceae)

This report deals with micropropagation of the critically endangered and endemic Turkish shrub, Thermopsis turcica using callus, root and cotyledonary explants. Callus cultures were initiated from root and cotyledon explants on MS medium supplemented with 0.5–20 μM NAA or 2,4-D. The root explants were found to be better in terms of quick responding and callusing percentages as compared to the cotyledons. Organogenic callus production with adventitious roots and shoots were obtained on MS medium with only NAA. The calli obtained with NAA, root and cotyledonary explants were cultured with BA and kinetin (2–8 μM) alone or in combination with a low level (0.5 μM) of 2,4-D or NAA. The best regeneration of shoots from root explants was observed on hormone-free MS medium. NAA with BA or kinetin in the medium improved shoot induction from the calli obtained with NAA. Maximum percentage of shoots (93.3%), maximum number of shoots (6.2) and maximun length of shoots (8.22 cm) were achieved from cotyledonary explants at 4 μM BA and 0.5 μM NAA. The presence of 0.5 μM or higher levels of 2,4-D in shoot induction medium inhibited the regeneration in T. turcica explants. 83% of in vitro rooting was attained on pulsed-IBA treated shoots. The regenerated plants with well developed shoots and roots were successfully acclimatized. Application of this study’s results has the potential to conserve T. turcica from extinction.     

Sugarbeet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.): shoot regeneration from callus and callus protoplasts

The successful application of recombinant DNA technology for crop plants requires efficient regeneration systems. A detailed study on the regeneration potential of callus and callus-derived protoplasts of a recalcitrant species, sugarbeet, was performed. A reproducible and highly efficient method for induction of regenerable friable callus was established from etiolated hypocotyl explants. A reduced sucrose concentration proved beneficial. Successful shoot regeneration could be demonstrated in 10 out of 12 tested lines. Seed germination, followed by callus induction and shoot regeneration required only a single culture medium. Additionally, the regeneration capacity of roots and root-derived callus was demonstrated. Highly efficient plant regeneration was also achieved when using protoplasts isolated from regenerable friable callus induced on etiolated hypocotyls explants. To our knowledge this represents the first report on callus protoplast to plant regeneration in sugarbeet.     

High-frequency somatic embryogenesis from germinated zygotic embryos of <Emphasis Type="Italic">Schisandra chinensis</Emphasis> and evaluation of the effects of medium strength,sucrose, GA<Subscript>3</Subscript>, and BA on somatic embryo development

We developed a new protocol for highly efficient somatic embryogenesis and plantlet conversion of Schisandra chinensis. Friable embryogenic callus was induced from cotyledonary leaves and hypocotyls of germinated zygotic embryos on Murashige and Skoog (MS) agar medium containing 2,4-dichlorophenoxyacetic acid (2,4-D). Preculture of zygotic embryos on 2,4-D-containing medium increased embryogenic callus induction efficiency. The highest embryogenic callus induction frequency of 56.7% was obtained from shoot apical meristem-containing hypocotyl explants from 1-week-old germinated embryos on MS medium containing 4.0 mg l⁻¹ 2,4-D. Embryogenic callus proliferation, somatic embryo (SE) formation, and subsequent plantlet conversion occurred under optimal culture conditions. The effects of MS medium strength, sucrose, gibberellic acid (GA₃), and 6-benzyladenine (BA) on SE formation and plantlet conversion were evaluated. Low MS medium strength (1/4 to 1/2) was necessary for SE formation, and the optimal sucrose concentration was 2.0%. Supplementing medium with GA₃ negatively impacted SE formation and subsequent development. BA significantly increased the number of SEs and the plantlet conversion capacity. One-third-strength MS medium with 1.0% sucrose and 0.5 mg l⁻¹ BA produced the highest number of SEs (309 embryos from 9 mg embryogenic callus) and the highest frequency of plantlet conversion from germinated SEs (52.6%). When transplanted to soil, 90% of the regenerated plants developed into normal plants.     

Somatic embryogenesis and organogenesis in Dendrocalamus hamiltonii

In this study, mature zygotic embryos, plant growth regulators, and various media were tested with the aim of developing an efficient regeneration system for plantlets of the bamboo species Dendrocalamus hamiltonii. Callus formation was induced in explants cultured in Murashige and Skoog (MS) medium supplemented with 1.0–3.0 mg/l 2,4-dichlorophenoxyacetic acid. Optimal shoot differentiation and subsequent shoot growth were also obtained in MS medium supplemented with 2 mg/l benzyladenine, 1 mg/l kinetin, and 1 mg/l naphthaleneacetic acid. Root induction was enhanced by the addition of 5 mg/l indole-3-butyric acid to the culture medium. Histological analysis revealed that both somatic embryogenesis and organogenesis were induced during callus initiation, shoot differentiation, and the development of plantlets from the mature zygotic embryos. Our data provide a useful basis for developing culture protocols for the regeneration of bamboo plants.     

High frequency plant regeneration from immature embryos of an elite barley cultivar (Hordeum vulgare L. cv. Morex)

An efficient plant regeneration system was developed for Hordeum vulgare L. 'Morex' barley, an important United States malting cultivar. The protocol was based on a series of experiments involving the sizes of immature embryos and the culture media. We found that the embryo size is critical for the establishment of embryogenic callus. Smaller embryos (0.5-1.5 mm) showed a much higher ability to produce embryogenic callus capable of regenerating green plants with fewer albinos than did the larger embryos (1.6-3.0 mm). Either 3 mg/l 2,4-dichlorophenoxyacetic acid or dicamba in modified Murashige and Skoog's (MS) medium was optimum for the induction of embryogenic callus. The embryogenic callus maintained high regeneration during six subcultures in the callus induction medium. Efficient shoot regeneration was obtained on modified MS medium containing 0.5-1.0 mg/l 6-benzylaminopurine (BA). Regenerated shoots were rooted on half-strength MS medium containing 0.2 mg/l IBA. Plants were successfully transferred to soil and grown to maturity in the greenhouse. This efficient plant regeneration system provides a foundation for generating transgenic plants of this important barley cultivar.     

以根为外植体建立大蒜的组织培养体系

以国内4个大蒜栽培品种为材料,建立了以根为外植体的再生体系。将蒜瓣去皮后灭菌消毒,萌发后选取苗龄为5~7 d的无菌苗的根接种到含不同激素配比的培养基中进行愈伤组织诱导,发现MS+2,4-D 1 mg/L+2ip 0.1 mg/L组合愈伤诱导效率最高,平均为56.06%;愈伤组织经过2~3次继代培养,选取胚性愈伤组织置于不同分化培养基上进行培养,2~3个月后可见小芽产生,分化培养基为MS+KT 1 mg/L时,植株再生效率最高,平均达到35.01 %。本研究建立了一种以根为外植体的高效的大蒜愈伤诱导和再生体系,为大蒜遗传转化体系的建立打下良好基础。     

<Emphasis Type="Italic">In vitro</Emphasis> plant regeneration through somatic embryogenesis and direct shoot organogenesis in <Emphasis Type="Italic">Pennisetum glaucum</Emphasis> (L.) R. Br.

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.     

芍药花药愈伤组织诱导及体细胞胚发生

以芍药(Paeonia lactiflora)品种粉玉奴花药为外植体, 研究不同浓度2,4-D对愈伤组织诱导、体胚发生及植株再生的影响, 采用组织细胞学方法观察愈伤组织以及体细胞胚发育过程, 采用根尖染色体法鉴定再生植株倍性。结果表明, 芍药花药愈伤组织诱导的最适培养基为MS+1 mg·L^-12,4-D+1 mg·L^-1 NAA+0.1 mg·L^-1 KT+30 g·L^-1蔗糖+6.5 g·L^-1琼脂, 愈伤组织诱导率为14.7%。转入体细胞胚诱导培养基上, 历经球形胚、心形胚、鱼雷胚和子叶胚阶段, 体胚诱导率为52.1%; 在成苗培养基中能够长出真叶并得到完整植株, 成苗率为47.1%。经根尖染色体法鉴定出单倍体和二倍体植株。该研究初步建立了通过体细胞胚间接发生途径实现植株再生的培养体系, 可为芍药属其它品种的花药培养提供借鉴, 获得的再生植株是芍药遗传学研究和育种工作的重要材料。     

诱导茶树成熟胚培育成幼苗的研究

以茶树品种——农抗早的成熟胚为外植体离体培养,初次研究了2,4-D、6-BA等不同植物激素对茶树成熟胚诱导成幼苗的影响。结果表明,在合适的激素组合条件下,愈伤组织诱导为97%,在附加2.5mg/L 6-BA 0.5mg/L NAA的MS培养基上,愈伤组织的芽分化率为14.2%,附加1.5mg/L NAA的1/2 MS培养基,幼苗的根分化率为5%。     

Shoot Regeneration from Cultured Leaf Explants of Lycium barbarumand Agrobacterium-Mediated Transformation1

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.     

Callus induction and high-efficiency plant regeneration via somatic embryogenesis in <Emphasis Type="Italic">Papaver nudicaule</Emphasis> L., an ornamental medicinal plant

We describe culture conditions for a high-efficiency in vitro regeneration system of Papaver nudicaule through somatic embryogenesis and secondary somatic embryogenesis. The embryogenic callus induction rate was highest when petiole explants were cultured on Murashige and Skoog (MS) medium containing 1.0 mg l⁻¹ α-naphthaleneacetic acid (NAA) and 0.1 mg l⁻¹ 6-benzyladenine (BA) (36.7%). When transferred to plant growth regulator (PGR)-free medium, 430 somatic embryos formed asynchronously from 90 mg of embryogenic callus in each 100-ml flask. Early-stage somatic embryos were transferred to MS medium containing 1.0 mg l⁻¹ BA and 1.0 mg l⁻¹ NAA to germinate at high frequency (97.6%). One-third-strength MS medium with 1.0% sucrose and 1.0 mg l⁻¹ GA₃ had the highest frequency of plantlet conversion from somatic embryos (91.2%). Over 90% of regenerated plantlets were successfully acclimated in the greenhouse. Secondary somatic embryos were frequently induced directly when the excised hypocotyls of the primary somatic embryos were cultured on MS medium without PGRs. Sucrose concentration significantly affected the induction of secondary embryos. The highest induction rate (89.5) and number of secondary somatic embryos per explant (9.3) were obtained by 1% sucrose. Most secondary embryos (87.2–94.3%) developed into the cotyledonary stage on induction medium. All cotyledonary secondary embryos were converted into plantlets both in liquid and on semisolid 1/3-strength MS medium with 1.0% sucrose.     

Comparison of in vitro regeneration pathways in <Emphasis Type="Italic">Punica granatum</Emphasis> L.

When cotyledonary explants, excised from in vitro germinated seedlings, of pomegranate (Punica granatum L.) were incubated on solid Murashige and Skoog (1962) medium supplemented with 21 μM naptheleneacetic acid (NAA) and 9 μM 6-benzyladenine (BA), 80% of explants developed callus. A high frequency of shoot organogensis was obtained when explants were incubated on MS medium supplemented with 8 μM BA, 6 μM NAA, and 6 μM giberrellic acid (GA₃). However, adding 24 μM silver nitrate (AgNO₃) to this medium markedly enhanced shoot regeneration frequency (63%) and mean number of shoots per explant (11.26) and length of shoots (2.22 cm). Highest frequency of in vitro rooting, mean number of roots/shoot (4.32), and mean root length (2.71 cm) were obtained when regenerated shoots were transferred to half-strength MS medium supplemented with 0.02% activated charcoal. Well-rooted plantlets were acclimatized, and then transferred to soil medium. Moreover, when zygotic embryos of P. granatum, excised from seeds collected at 16 weeks following full bloom, were incubated on MS medium containing 30 g l⁻¹ sucrose, 15% coconut water, 21 μM NAA, and 9 μM BA, they developed the highest frequency of embryogenic callus, clumps with globular embryos, and mean number of both globular and heart-shaped embryos per callus clump. Subjecting zygotic embryo explants to six-week dark incubation period was essential for embryogenic callus induction, and these were subsequently transferred to 16 h photoperiod for further growth and development of somatic embryos. Germination of somatic embryos was observed when these were transferred to MS medium was supplemented with 60 g l⁻¹ sucrose.     

Embryo rescue and plant regeneration in banana (<Emphasis Type="Italic">Musa</Emphasis> spp.)

An efficient regeneration protocol for zygotic embryos at varying maturity stages was developed for wild banana (Pisang Jajee (AA)). Embryo ontogeny was studied to determine the best maturity stage for embryo rescue, suitable media and culture conditions (light and dark) for germination and regeneration. The conversion of endosperm from transparent fluid into a semi-solid state was followed by visible embryo development, which commenced only after 70% embryo maturity. Zygotic embryos of Pisang Jajee at different maturity levels were excised and cultured on medium fortified with different concentrations of 6-benzyl adenine (BA) and indole acetic acid (IAA). Zygotic embryos produced callus or plantlets 25 days after initiation. The frequency of callus induction was greater in immature embryos irrespective of the media composition and decreased with increasing maturity. Fully matured embryos regenerated directly into plantlets without producing callus. Immature embryos required medium supplemented with plant growth regulators (PGRs) for successful regeneration. Although the culture conditions had no influence, dark conditions favoured callus induction and plant regeneration.     

Thidiazuron-induced high-frequency shoot organogenesis from leaf-derived callus of ia medicinal climber, <Emphasis Type="Italic">Tylophora Indica</Emphasis> (Burm. F.) merrill

Summary Tylophora indica (Burm. f.) Merrill is a threatened medicinal climber distributed in the forests of northern and peninsular India. An efficient and reproducible protocol for high-frequency callus regeneration from immature leaf explants of T. indica was developed. Organogenic callus formation from immature leaf pieces was obtained by using Murashige and Skoog (MS) medium supplemented with 7 μM 2,4-dichlorophenoxyacetic acid and 1.5 μM 6-benzyladenine. On this medium 92% explants produced callus. The optimal hormone combination for plantlet regeneration was 8 μM thidiazuron, at which shoot regeneration was obtained from 100% of the cultures, with an average of 66.7 shoots per culture. Histological studies of the regenerative callus revealed that shoot buds were originated from the outermost regions. For root formation, half-strength MS medium supplemented with 3 μM indole-3-butyric acid was used. Plants were transferred to soil, where 92% survived after 3 mo. of acclimatization.     

多年生黑麦草成熟胚再生体系的建立及基因枪转化

目的:建立以多年生黑麦草成熟胚为起始材料的再生体系,用于基因枪转化。方法:多年生黑麦草成熟种子在附加 5mg L 2,4 D的MS培养基上诱导愈伤组织,转至新继代培养基上产生胚性愈伤组织。分化培养基为无激素MS培养基。再生植株在培养基成分减半的无激素MS培养基生根,之后移栽至土壤。基于这一再生体系,用含有水稻几丁质酶基因RC2 4的质粒pARN6和含有草丁膦乙酰转移酶基因Bar的质粒pDB1,通过基因枪轰击胚性愈伤组织。用附加PPT的继代培养基进行转化植株的抗性筛选。结果:共获得 2 4 3株再生植株。通过PCR进行检测,获得1 8株整合有RC2 4基因的植株,1 5株整合有Bar基因的植株,同时转入 2个基因的植株 2株。     

骨干玉米自交系丹598遗传再生体系的建立

目的:以玉米骨干自交系丹598的幼胚为外植体,诱导愈伤组织建立遗传再生体系。方法:探讨胚龄、培养基种类、2,4-D浓度对愈伤组织诱导的影响。结果:在授粉后16～18 d,2,4-D浓度为2.0 mg/L时诱导最佳;设置N6、NB、改良NB、MS、MB等5种培养基,筛选出改良NB培养基为最佳诱导培养基;分化培养基中添加1 mg/L激动素、0.5 mg/L 6-卞基嘌呤和0.5 mg/L萘乙酸能促进绿苗分化和根系生长。结论:建立了玉米自交系丹598的优良再生体系,为以后的基因转化工作打下了良好基础。     

Callus induction and plant regeneration from mature embryos of sunflower

Callus development and efficient shoot and root organogenesis were obtained from five different sunflower (Helianthus annuus L.) genotypes: Trakya 80, Trakya 129, Trakya 259, Trakya 2098, and Viniimk 8931, which are commercially important for Turkey. Plant tissue culture systems were established on Murashige and Skoog (MS) media supplemented with various plant growth regulators using mature embryos of sunflower. For callus induction MS + 1 mg/l 2,4-D, for shoot regeneration MS + 1 mg/l benzyladenine and 0.5 mg/l α-naphthaleneacetic acid were used. Callus induction ratios were around 80–92% in all tested genotypes. The Trakya 259 genotype gave the best shoot regeneration response (44%). All regenerated shoots were rooted on MS medium supplemented with 1 mg/l indolyl-3-butyric acid and on MS medium without any hormones. Mature embryos could be an alternative source for indirect plant regeneration and gene transfer systems for different sunflower genotypes. Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 4, pp. 621–624. The text was submitted by the authors in English.     

Efficient callus induction and plant regeneration from mature embryo culture of winter wheat (Triticum aestivum L.) genotypes

Immature and mature embryos of 12 common winter wheat (Triticum aestivum) genotypes were cultured in vitro to develop an efficient method of callus formation and plant regeneration from mature embryo culture, and to compare the responses of both embryo cultures. Fifteen days after anthesis, immature embryos were aseptically dissected from seeds and placed with the scutellum upwards on a solid agar medium containing the inorganic components of Murashige and Skoog (MS) and 2 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). Mature embryos were moved slightly in the imbibed seeds. The seeds with moved embryos were placed furrow downwards in dishes containing 8 mg/l 2,4-D for callus induction. The developed calli and regenerated plants were maintained on 2,4-D-free MS medium. Plants regenerated from both embryo cultures were vernalized and grown to maturity in soil. Regenerated plantlets all maintained the hexaploid chromosome number. A strong genotypic effect on the culture responses was found for both explant cultures. Callus induction rate, regeneration capacity of callus and number of plants regenerated were independent of each other. Mature embryos had a high frequency of callus induction and regeneration capacity, and therefore, being available throughout the year, can be used as an effective explant source in wheat tissue culture. Received: 4 February 1997 / Revision received: 1 April 1997 / Accepted: 5 May 1997     

Somatic embryogenesis and regeneration of Cenchrus ciliaris genotypes from immature inflorescence explants

An efficient, highly reproducible system for plant regeneration via somatic embryogenesis was developed for Cenchrus ciliaris genotypes IG-3108 and IG-74. Explants such as seeds, shoot tip segments and immature inflorescences were cultured on Murashige and Skoog (MS) medium supplemented with 2.0–5.0 mg dm^?3 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.5 mg dm^?3 N⁶-benzyladenine (BA) for induction of callus. Callus could be successfully induced from all the three explants of both the genotypes. But the high frequency of embryogenic callus could be induced only from immature inflorescence explants. Somatic embryos were formed from nodular, hard and compact embryogenic calli when 2,4-D concentration was gradually reduced and BA concentration increased. Histological studies of somatic embryos indicated the presence of shoot apical meristem with leaf primordia. Ultrastructural details of globular and scutellar somatic embryos further validated successful induction and progression of somatic embryogenesis. Shoots were differentiated upon germination of somatic embryos on MS medium containing 2,4-D (0.25 mg dm^?3) and BA or kinetin (1–5 mg dm^?3). Roots were induced on ½ MS medium containing charcoal (0.8 %), and the regenerated plants transferred to pots and established in the soil showed normal growth and fertility.