Factors Affecting Plant Regeneration from Tissue Cultures of Chinese Leymus (Leymus chinensis)

Chinese leymus (Leymus chinensis Trin.) is a perennial grass of the Gramineae, which is widely distributed in China, Mongolia and in Russian-Siberian. In order to explore the potential of biotechnology for genetic improvement of this forage grass, an efficient tissue culture system was established and the factors affecting plant regeneration were evaluated. Immature inflorescence segments 3–5 mm in length from eight accessions were cultured on N6 medium supplemented with 2.26–22.60 µM 2,4-D. The callus induction frequency ranged from 72.11 to 82.19%. Shoots were differentiated from the calli on N6 medium containing 4.65 µM kinetin and 4.44 µM BA. Viable regenerants were developed on hormone-free medium. Normal plants were obtained after natural vernalization in the field. The plant regeneration frequency in Chinese leymus was associated with different genotypes and different combinations of growth regulators in medium. The concentration of 2,4-D in the callus induction medium had a strong effect on successive plant regeneration. Relatively higher concentrations of 2,4-D (i.e., 9.04 and 22.60 µM) were more favorable to the plant regeneration than lower ones (i.e., 2.26 and 4.52 µM). This is the first report on plant regeneration in vitro in L. chinensis.     

In vitro Shoot Regeneration from Leaves of Sweet Cherry (Prunus avium) 'Lapins' and 'Sweetheart'

Shoot regeneration was achieved from leaves of in vitro cultures of Prunus avium L. cv. 'Lapins' and 'Sweetheart' using woody plant medium (WPM) supplemented with 1-naphthalene-acetic acid (NAA) and thidiazuron (TDZ) or benzyladenine (BA). Percent regeneration was influenced by plant growth regulators and by explant type, orientation and wounding. Optimal regeneration was observed with whole-leaf explants wounded by transverse cuts along the midrib and incubated abaxial surfaces uppermost, on media supplemented with 2.27 or 4.54 µM TDZ plus 0.27 µM NAA. The percent regeneration of the two cultivars was not significantly different. Optimum conditions for regeneration resulted in 71.4% of 'Lapins' and 54% of 'Sweetheart' explants producing one or more shoots per explant.     

In vitro plant regeneration of caper (<Emphasis Type="Italic">Capparis spinosa</Emphasis> L.) from floral explants and genetic stability of regenerants

A new technique to regenerate caper plants (Capparis spinosa L. subsp. rupestris) starting from flower explant is reported. In vitro plant regeneration was attempted using stigma, anthers and unfertilized ovules of unopened flowers collected in the field. Plant regeneration was achieved from unfertilized ovules on MS medium supplemented with 88 mM sucrose and 13 μM 6-benzyladenine (BA). New individuals obtained from unfertilized ovules were used as source material for micropropagation and multiple shoots were obtained on MS medium supplemented with the adeninic cytokinin BA and the auxin indole-3-butyric acid (IBA). Explants obtained in micropropagation step were used for rooting step under several treatments. The best results (100% of rooted explants) were obtained when explants were dipped for 10 min in 50 μM IBA solution and successively maintained in growth regulator free medium. New plants were vigorous, of good quality and presented phenotypic characters similar to mother plants. Furthermore genetic stability of regenerants was verified through flow cytometric analysis and two different DNA-based techniques.     

Thidiazuron-induced regeneration of <Emphasis Type="Italic">Echinacea purpurea</Emphasis> L.: Micropropagation in solid and liquid culture systems

The goals of this study were to investigate thidiazuron (TDZ)-induced morphogenesis of Echinacea purpurea L. and to assess the possibility of developing a liquid-based protocol for rapid micropropagation. Callus development and root organogenesis were observed on leaf explants cultured on media containing 2,4-dicholorophenoxyacetic acid or dicamba, but no plantlets were regenerated. Addition of TDZ to the culture medium as the sole growth regulator resulted in the production of regenerable callus cultures. The highest rate of regeneration was observed for explants cultured on medium with TDZ at 2.5 μM or higher. Tissue derived from 1.0 μM TDZ treatments was used to initiate liquid cultures. All liquid treatments produced a similar number of regenerants but significantly more healthy plants were obtained from cultures grown in the presence of 0.1 and 1.0 μM TDZ. This TDZ-based micropropagation system is the first liquid, large-scale propagation protocol developed for the mass production of E. purpurea plants.     

Adventitious shoot regeneration fromFagus sylvatica leaf explantsin vitro

Summary Adventitious shoots were induced on transversally divided expanding leaves fromFagus sylvatica shoot cultures of juvenile origin. Adventitious shoot buds formed mainly on callus that developed on the petiole stump or on the cut across the midrib of distal leaf halves. However, sometimes they arose directly from leaf tissue. An anatomical study confirmed both the direct and indirect origin of the adventitious buds. The best results were obtained by culturing proximal leaf sections on woody plant medium supplemented with 2.9 μM indole-3 acetic acid in combination with 8.9 μM benzyladenine or 2.3 μM thidiazuron (TDZ). Proximal explants were more responsive than distal explants in terms of both callus formation and bud regeneration, regardless of the induction medium or clone tested. Bud formation capacity was influenced by the genotype of the stock shoot culture and was enhanced by an initial 10 d darkness, but was inhibited by longer periods of darkness. Caulogenic competence was significantly affected by the duration of exposure to TDZ; in particular, adventitious shoot length was depressed by increasing the exposure period. Three weeks culture with TDZ was the most efficient treatment for shoot production and elongation. Further shoot development was promoted by subculturing the explants to the same medium used for the maintenance of the stock shoot cultures. Shoots so obtained were multiplied and rooted producing plantlets of adventitious origin.     

In vitro plant regeneration from seedling-derived explants of ramie [Boehmeria nivea (L.) Gaud]

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.     

In vitro regeneration of wild pear (<Emphasis Type="Italic">Pyrus pyraster</Emphasis> Burgsd) clones tolerant to Fe-chlorosis and somaclonal variation analysis by RAPD markers

An in vitro adventitious regeneration system under selective pressure was established in Pyrus pyraster Burgsd to obtain somaclones with higher adaptability to calcareous soils. P. pyraster is important species, both for its relative closeness to cultivated pear and for reforestation of marginal farmland and for the production of timber. Shoot regeneration was induced from leaves and vegetative apices of in vitro-grown shoots on a modified LP medium supplemented with naphtaleneacetic acid (1.07 μM) and benziladenine (BA, 8.9 μM). After 30 days, explants were transferred to an expression medium consisting of the same basal medium with only BA present. Selective treatments utilized MS medium with Fe-EDTA replaced by equimolar amount of FeSO4 with either KHCO₃ or NaHCO₃. Through the selection process 11 putatively tolerant lines were obtained from vegetative shoot apices. RAPD analysis was performed on these lines to allow comparison to the mother clone. A total of seven 10-mer primers were used to amplify all the genotypes and 74 scorable fragments were produced. These were analysed using the Dice similarity index, showing genetic variability among the 11 regenerated clones and between them and the mother clone.     

Micropropagation ofPenstemon serrulatus and iridoid formation in regenerated plants

A method for the micropropagation ofPenstemon serrulatus Menz. from shoot tips or nodal segments was developed. Multiple microshoot cultures (up to 20 shoots from a single explant) were obtained by maintenance of shoot tip explants on Schenk & Hildebrandt medium (SH) supplemented with 4.4 µM benzyladenine (BA) or 8.9 µM BA and 0.57 µM indole-3-acetic acid (IAA). Microshoots developed into numerous, normal shoots when explants were transferred to SH medium containing 2.9 µM IAA or 2.5 µM indole-3-butyric acid (IBA). Shoot cultures were also established from nodal segments (max. 6.8 shoots per segment) when they were placed on SH medium with 0.49 µM IBA and 2.2 µM BA. Rooting of shoots was better on SH medium containing auxin (IBA, NAA or IAA) than on SH medium without growth regulators. The plantlets were then transferred to pots and grown in the greenhouse. Four-month-old regenerated plants demonstrated similar iridoid content (leaves contained 3.83% dry wt. penstemide and 1.8% dry wt. serrulatoloside) as the original plants.     

Efficient in vitro regeneration of fertile plants from corm explants of Hypoxis hemerocallidea landrace Gaza—The “African Potato”

We present efficient protocols for the regeneration of fertile plants from corm explants of Hypoxis hemerocallidea Fisch. & C. A. Mey. landrace Gaza, either by direct multiple shoot formation or via shoot organogenesis from corm-derived calluses. The regeneration efficiency depended on plant growth regulator concentrations and combinations. Multiple direct shoot formation with high frequency (100% with 5–8 shoots/explant) was obtained on a basal medium (BM) supplemented with 3 mg/l kinetin (BM1). However, efficient indirect regeneration occurred when corm explants were first plated on callus induction medium (BM2) with high kinetin (3 mg/l) and naphthalene acetic acid (NAA 1 mg/l), and then transferred to shoot inducing medium (BM3) containing BA (1.5 mg/l) and NAA (0.5 mg/l). Shoot regeneration frequency was 100% and 30–35 shoots per explant were obtained. The regenerated shoots were rooted on a root inducing medium (BM4) containing NAA (0.1 mg/l). Rooted plantlets were transferred to the greenhouse. The regenerants were morphologically normal and fertile. Flow cytometric analyses and chloroplast counts of guard cells suggested that the regenerants were diploid. Efficient cloning protocols described here, have the potential not only to substantially reduce the pressure on natural populations but also for wider biotechnological applications of Hypoxis hemerocallidea—an endangered medicinal plant.     

Pretreatment in thidiazuron improves the in vitro shoot induction from leaves in Curculigo orchioides Gaertn., an endangered medicinal plant

Leaf regeneration via direct induction of adventitious shoots obtained from an endangered medicinal plant, Curculigo orchioides Gaertn. by pretreating with thidiazuron. C. orchioides is an endangered medicinal herb belonging to the family Hypoxidaceae. Direct inoculation of leaf pieces on MS medium supplemented with various concentrations of BAP (2–8 μM) or TDZ (2–8 μM) alone or in combination with NAA (0.5 and 1.0 μM) produced low shoot induction both in terms of % response and number of shoots per explant. Hence, leaf explants were pretreated with 15, 25 or 50 μM thidiazuron (TDZ), for 6, 24 or 48 h with the aim of improving shoot regeneration from cultured explants. After pretreatment, explants were transferred to an agar solidified MS medium that was supplemented with BAP (4 μM), TDZ (6 μM), BAP (4 μM) + NAA (1.0 μM), TDZ (6 μM) + NAA (0.5 μM). Control explants were incubated directly on the medium without any pretreatment. The pretreatment of explants with 15 μM TDZ for 24 h significantly promoted the formation of adventitious shoots and the maximum response was observed on MS medium supplemented with 6 μM TDZ. In this medium, 96 % cultures responded with an average number of 16.2 adventitious shoots per explant. The percentage of leaf explants producing shoots and the average number of shoots per explant were significantly improved when TDZ pretreated leaves were cultured onto MS medium supplemented with BAP or TDZ alone or in combination with NAA. The rooted plantlets were successfully transplanted to soil with 90% success. The present investigation indicated the stimulatory role of TDZ pretreatment in regulating shoot regeneration from leaf explants of C. orchioides.     

Efficient plant regeneration of native spearmint (Mentha spicata L.)

Summary Protocols and media constituents for efficient in vitro plant regeneration of Native Spearmint (Mentha spicata L. cultivar ‘Native Spearmint’) have been defined. Adventitious shoots were initiated either directly from morphogenetically competent cells of explants or primary callus. Leaf explants from at least 2-mo.-old in vitro-maintained shoots exhibited the greatest morphogenetic capacity. Explants derived from basal portions of leaves at the bottom of the shoot were most responsive, with up to a 100% regeneration frequency and greater than nine shoots per explant. Highest frequency of meristemoids and morphogenetic callus were initiated from explants cultured onto a basal medium containing Murashige and Skoog (MS) salts, supplemented with 4 mg thidiazuron (TDZ) per L and 25% (vol/vol) coconut water (CW) for 10 to 14 d in darkness. Bud and shoot development required removal of both TDZ and CW from the medium. Shoot propagules were transferred to basal medium supplemented with 0.01 mg α-naphthaleneacetic acid (NAA) per L and grown under low light for about 2 wk to facilitate shoot elongation. Individual shoots about 1 cm tall were dissected and retransferred onto the same medium. Root initiation began within 4 to 6 d and a functional root system developed within 2 to 3 wk. These plantlets were transferred to soil and acclimated successfully for growth and development in a greenhouse. This is the first report of an efficient regeneration system for Native Spearmint based on adventitious organogenesis.     

Somatic embryogenesis of Agave victoria-reginae Moore

Plant regeneration through direct somatic embryogenesis of leaf blade explants from in vitro propagated plants of Agave victoria-reginae Moore, is described. Somatic embryogenesis was evident in a 6-week period on agarsolidified MS medium supplemented with L2 vitamins and 2,4-dichlorophenoxyacetic acid (1,4 µM), and germination of somatic embryos was achieved after 8 weeks on half-strength MS medium and 4 weeks on half-strength SH medium, both lacking growth regulators. Hyperhydricity of somatic embryos and plantlets was reduced by the use of vented culture vessel lids during the last 4 weeks on SH medium. Shoot proliferation was obtained, and hyperhydricity was eliminated on a modified MS medium (with NH₄NO₃ reduced to 5 mN) supplemented with kinetin (4.6 µM) and 1-naphthaleneacetic acid (1.6 µM) and the use of vented culture vessel lids.Abbreviations 2,4-d 2,4-dichlorophenoxyacetic acid - NAA 1-naphthaleneacetic acid - MS Murashige and Skoog - LOG-1 MS modified medium by Castro-Concha et al. (1990) - L2 Phillips and Collins (1979) vitamins - SH Schenk and Hildebrandt     

Micropropagation of Two Australian Native Fruit Species,Davidsonia pruriens and Davidsonia jerseyana G. Harden & J.B. Williams

Nodal explants from in vitro grown seedlings of Davidsonia pruriens and D. jerseyana, established on MS media were treated with various concentrations of three cytokinins. D. pruriens developed optimum shoot growth in terms of shoot height and number of leaves per shoot when 1.0 µM BA was added to basal MS medium while optimum shoot growth for D. jerseyana was obtained when 0.01 µM 2iP was added to the medium. Optimum root initiation and development was obtained when actively growing axillary shoots were cultured on 1/2MS medium plus 32.2 µM IBA for 3–5 days for D. pruriens and 2–3 days for D. jerseyana before transfer to PGR-free medium containing 10 µM riboflavin. Root initiation of more than 80% was achieved with multiple genotypes of D. pruriens and three genotypes of D. jerseyana using juvenile material. The plantlets were transferred to pots and grown in the greenhouse with a success rate of 60% for D. pruriens and 75% for D. jerseyana. Adult D. jerseyana stem explants produced 2–5 shoots per nodal explant upon treatment with 0.1 µM BA. Side shoots from adult D. jerseyana produced similar results for shoot multiplication as for juvenile material. Protocol for multiplication of adult D. pruriens was achieved with much greater difficulty by using material from the green house. Axillary shoots were initiated when 100 µM TDZ was applied to the stem of an adult pot plant and the resultant side shoots were cultured on MS medium containing 1.0 µM BA and 1.0 µM GA₃.     

In vitro plant regeneration of Arachis correntina (Leguminosae) through somatic embryogenesis and organogenesis

In vitro protocols for plant regeneration of Arachis correntina through both somatic embryogenesis and organogenesis were developed using immature leaves as explants. Morphologically normal somatic embryos were obtained on culture media composed of 20.70 or 41.41 μM picloram (PIC) with the addition of 0.044 μM 6-benzylaminopurine (BA), resulting in a 33 and 24% of conversion into plants, respectively. The source of explants and the developmental stage of the leaves had a marked effect on somatic embryogenesis. The second folded immature leaves from in vitro growing plants were the most responsive producing up to 30% embryogenesis in MS+41.41 μM PIC. Embryos converted into plants after transfer to MS medium devoid of growth regulators and these plants were successfully acclimatised. Adventitious shoots were obtained on culture media supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) or naphthaleneacetic acid (NAA) with or without 0.044 μM BA, achieving plant regeneration in the induction media. The highest percentage of bud formation was obtained on culture medium composed of␣MS+10.74 μM NAA+0.044 μM BA (12.5%). Roots were formed on all culture media tested. Regenerated plants were transferred to pots and grew well under greenhouse conditions.     

Plant regeneration from in vitro leaves of the peach rootstock ‘Nemaguard’ (<Emphasis Type="Italic">Prunus persica</Emphasis> × <Emphasis Type="Italic">P. davidiana</Emphasis>)

A complete protocol for adventitious shoot regeneration was developed from the leaves of peach rootstock ‘Nemaguard’(Prunus persica × P. davidiana) grown in vitro. Shoot explants were cultured in vitro in Murashige and Skoog medium supplemented with 3.55 μM 6-benzyladenine and 7.38 μM indole-3-butyric acid (IBA). Non-expanded leaves along with their petioles from 3-week-old in vitro-grown shoots were used as explants. Regeneration percentage was influenced by plant growth regulators, basal medium, explant type, dark period, and gelling agents. Optimal regeneration was observed with leaf explants wounded by transverse cuts twice along the midrib and first incubated with abaxial surfaces facing upward in the dark for 3 weeks, and then transferred to the light and cultured with the adaxial side in contact with regeneration medium, as seen on 1/2 MS, woody plant medium or Schenk and Hildebrandt medium supplemented with 9.08 μM thidiazuron, 0.54 μM IBA and 0.25% agar. This produced the highest regeneration percentage at 71.7% and a mean of 5.74 ± 3.24 shoots on 1/2 MS medium. Adventitious shoots were rooted (98.3–100%) and rooted plantlets survived after acclimatization to the greenhouse.     

High efficiency plant regeneration from petiole explants of Carica papaya L. through organogenesis

Callus cultures were obrained from petiole explants of Carica papaya on MS medium containing 0.5–10.5 μM α-naphthaleneacetic acid (NAA) in combination with 0.5–5 μM benzyladenine (BA). Hard-green calli were transferred to MS medium containing 100 mgl⁻¹ casein hydrolysate (CH) with specific BA-NAA formulation, where they developed adventitious buds within 2 weeks of culture. Maximum number of adventitious buds were obtained in 2 μM BA and 0.1 μM NAA. Shoot regeneration occurred from these adventitious buds by the end of the 4th week. Regenerated shoots were elongated in hormone-free medium and rooted in half-strength MS fortified with 3 UM NAA and 0.5 μM gibberellic acid (GA₃). The regenerants were transferred to soil after acclimatization.     

Transformation of a Texas cotton cultivar by using Agrobacterium and the shoot apex

 Transgenic cotton (Gossypium hirsutum L.) plants of a Texas cultivar CUBQHRPIS were obtained using Agrobacterium-mediated transformation coupled with the use of shoot-apex explants. After inoculation with A. tumefaciens strain LBA 4404 containing the pBI121 plasmid, regeneration of primary plants was carried out in a medium containing kanamycin (100  mg l^-1). Progeny obtained by selfing were germinated in the greenhouse and selected for expression of the T-DNA marker gene encoding neomycin phospho-transferase II (NPTII) by painting kanamycin (2%) on the leaves. Plants that survived the leaf painting were analyzed by DNA blots. Evidence for integration of the transgene (GUS) was observed in two successive generations from the regenerants (T₀). The transformed plants appeared to have more than one copy of the T-DNA. Received: 1 June 1998 / Accepted: 28 July 1998     

Direct and Indirect Shoot Organogenic Pathways in Epicotyl Cuttings of Troyer Citrange Differ in Hormone Requirements and in their Response to Light

Bud differentiation by direct organogenesis at the apical endof Troyer citrange (Citrus sinensis[L]. OsbeckxPoncirus trifoliata[L].Raf.) epicotyl cuttings inserted vertically in a semi-solidculture medium did not require hormone additions. The numberof buds regenerated was slightly, but significantly, increasedwhen the incubation was performed in the light as compared tothe dark, and by the addition of benzyladenine (BA; 2.2 to 22µM) to the medium. Bud sprouting and subsequent shootformation required the addition of BA and was increased by lightto a higher extent than bud formation. The best response wasobtained with the highest BA concentration tested (22 µM).Regeneration through the indirect organogenic pathway at thetwo edges of the epicotyl cuttings when in contact with theculture medium did not occur in the absence of benzyladenine,which was an absolute requirement for callus development. Thebest regeneration response was obtained when the explants wereincubated in the light in the presence of 4.4 µM BA andan auxin. Indole-3-acetic acid (IAA; 5.8 µM) was moreeffective in increasing shoot formation than naphthaleneaceticacid (NAA; 0.54 µM). Higher NAA concentrations inhibitedshoot formation. Incubation in the dark or increasing the BAconcentration (22 µM) increased markedly callus growth,but inhibited both bud differentiation and sprouting, almostcompletely suppressing shoot formation. The conditions duringregeneration affected the rooting of the regenerated shoots.Rooting of 86% of the shoots was achieved in a medium with 2.7µM NAA and 2.6 µM indole-3-butyric acid. All therooted explants acclimated and survived transplanting. Underthe optimal conditions tested, the proliferation rate obtainedthrough the indirect regeneration pathway ranged from 60 to86 plants per seedling. Copyright 2000 Annals of Botany Company Troyer citrange, Citrus sinensisxPoncirus trifoliata, auxins, benzyladenine, direct organogenesis, hormone requirement, indirect organogenesis, light, morphogenesis, rooting.     

Direct Differentiation of Shoot Buds from Leaf Explants of Cajanus Cajan L.

A protocol was developed for direct differentiation of multiple shoot buds from leaf explants of Cajanus cajan. In a modified Murashige and Skoog's medium supplemented with 2.22 µM benzyladenine (BA), 0.57 µM indole-3-acetic acid (IAA) and 41 µM adenine sulphate (AdS), the segments of basal halves of the first two leaves of a young seedling incubated on filter paper bridges in liquid medium took 20 – 25 d to differentiate shoot buds. The explants after transfer to solidified medium, with lower concentration of BA (0.22 M) resulted in fast growing healthy shoots. The developed shoots (measuring ca. 3 cm) were rooted in a medium supplemented with 1.42 µM IAA. They were subsequently grown in pots with soil with more than 80 % transplantation success.     

Differential Morphogenetic Responses of Cotyledonary Explants of Vigna mungo

The morphogenetic responses of cotyledonary nodal explants of Vigna mungo (L.) Hepper cv. VBN1 cultured on the same Murashige and Skoog's medium, B5 vitamins, and 13.31 µM N⁶-benzylaminopurine showed variations in the pattern of multiple shooting and morphology of leaves in dependence on initial explants (presence/absence of cotyledons). The regenerated shoots elongated in the initial medium and most of them rooted in the presence of 2.41 µM indole-3-butyric acid, and flowered in vitro. Rooted plants could be transferred to the field after hardening.