Indirect somatic embryogenesis and plant regeneration from leaf and internode explants of Paulownia elongata

Several plant growth regulators BA, TDZ, 2,4- and Kn were tested alone or in combination for their capacity to induce indirect somatic embryogenesis from leaf and internode explants of Paulownia elongata. Calli were produced when leaf explants were cultured on Murashige and Skoog (MS) medium containing 3 % sucrose, 0.4 % phytagel, 4 mg l^-1 TDZ and 0.1 mg l^-1 Kn after 3 weeks and the initiation rate was 54.1%. After subculturing on the same medium, embryos at various developmental stages (globular, heart and torpedo shaped) were transferred for maturation onto MS medium supplemented with 3 % sucrose, 0.4 % phytagel, 0.1 mg l^-1 TDZ, 1 mg l^-1 Kn and 2 mM glutamine. An average of 50.7 somatic embryos were obtained from 100 mg of embryogenic callus after 4 weeks at high frequency (64.7 %). Afterward, mature somatic embryos were isolated and cultured on hormone-free MS medium for germination (80 %) and development into plantlets. Plantlets were transferred to pots with a mixture of peat and perlite in a 3:1 ratio and showed a survival rate of 70–80 %. Plantlets regenerated by this procedure were morphologically identical to the donor material and developed normally in the greenhouse.     

A rapid protocol for somatic embryogenesis from immature leaflets of groundnut (Arachis hypogaea L.)

Summary Plant regeneration via somatic embryogenesis was developed in two groundnut varieties. Somatic embryogenesis was induced from immature leaflets on MS medium with different concentrations of the auxins 2,4-dichlorophenoxyacetic acid (2,4-D) or naphthaleneacetic acid (NAA) in combination with 0.5 mg/l of the cytokinin BA. The highest frequency of somatic embryo formation occurred on MS medium fortified with 20 mg 2,4-D per l. Of the two auxins tested individually 2,4-D was more effective for induction of embryogenesis as well as production of embryos. Embryo development and maturation was achieved on MS medium supplemented with N⁶-benzyladenine (BA) (0.5–2.0 mg/l) and 2,4-D (0.5 mg/l). Plant conversion frequency from somatic embryos was highest in presence of 2.0 mg BA per l and 0.5 mg NAA per l. The frequency of embryogenesis and plant regeneration was higher in the VRI-2 cultivar than in the other cultivar tested. Regenerated plants were transferred to soil, grown to maturity, and produced viable seeds.     

An efficient and rapid regeneration via multiple shoot induction from mature seed derived embryogenic and organogenic callus of Indian maize (Zea mays L.)

An efficient method for in vitro micro propagation and genetic transformation of plants are crucial for both basic and applied research. Maize is one of the most important cereal crops around the world. Regeneration from immature embryo is hampered due to its unavailability round the year. On the contrary mature embryo especially tropical maize is recalcitrant toward tissue culture. Here we report a highly efficient regeneration (90%) system for maize by using 2 different approaches i.e., embryogenic and organogenic callus cultures. Seeds were germinated on MS medium supplemented with 5 mg/l 2,4-D and 3 mg/l BAP. Nodal regions of 2 wks old seedlings were longitudinally split upon isolation and subsequently placed on callus initiation medium. The maximum frequency of embryogenic callus formation (90%) was obtained on MS medium supplemented with 2 mg/l 2,4-D and 1 mg/l BAP in the dark conditions. The compact granular organogenic callus formation (85% frequency) was obtained on MS medium supplemented with 2.5 mg/l 2,4-D and 1.5 mg/l BAP at light conditions. MS medium supplemented with 2 mg/l BAP, 1 mg/l Kinetin and 0.5 mg/l NAA promoted the highest frequency of shoot induction. The highest frequency of root formation was observed when shoots were grown on MS medium. The regenerated plants were successfully hardened in earthen pots after adequate acclimatization. The important advantage of this improved method is shortening of regeneration time by providing an efficient and rapid regeneration tool for obtaining more stable transformants from mature seeds of Indian tropical maize cultivar (HQPM-1).     

High-frequency somatic embryogenesis from small suspension-cultured clusters of cells of an interspecific hybrid of Oryza

Suspension cultures in which cell clusters were small and had a high capacity for somatic embryogenesis (about 60%) were established from immature panicles of F₁ plants from a cross between Oryza sativa and Oryza latifolia The cells were subcultured at seven-day intervals in a modified N6 medium. The cell clusters were quite small (approximately 30–200m in diameter) after culture for two months in this medium. When small clusters of cells were transferred to N6 medium, that had been diluted with an equal volume of water and supplemented with -naphthalenacetic acid (53 nM), 4-pyridylurea (2.2 M) and sucrose (30 gl^-1), somatic embryogenesis occurred at high frequency (about 60%). The system established in the present work is useful for biochemical and molecular biological research of the somatic embryogenesis in the Gramineae.Abbreviations 2,4-d 2,4-dichlorophenoxyacetic acid - NAA -naphthalenacetic acid - 4-PU 4-pyridylurea - MS Murashige and Skoog (1962)     

Direct somatic embryogenesis as a rapid and efficient system for in vitro regeneration of Arabidopsis thaliana

A simple, rapid and effective system to regenerate Arabidopsis plants via direct somatic embryogenesis has been established. Somatic embryogenesis was induced directly during culture of immature zygotic embryos. The frequency of somatic embryogenesis was strongly influenced by the stage of development of the explants. Explants in different developmental stages were cultured on B5 agar medium containing 5 M 2,4-dichlorophenoxyacetic acid and the highest frequency (up to 90%) of somatic embryogenesis was observed in zygotic embryos with fully-developed cotyledons. The first somatic embryos developing directly from explant tissue were noticed after 8 days of culture. Somatic embryogenesis of a high frequency (87–96%) was observed in cultures of the all six genotypes tested (Columbia, C-24, RLD, Wassilewskaja, Landsberg erecta and Wilna). Subculture of somatic embryos onto auxin-free medium resulted in their conversion into plants with an average frequency of 79.5%. The regenerates showed normal morphological characteristics and were fertile. All 56 analysed plants displayed a diploid number of chromosomes and two out of 96 (2.1%) tested plants carried a chlorophyll or embryo-lethal mutation.     

Efficient GA3-assisted plant regeneration from cell suspensions of three grape genotypes via somatic embryogenesis

Petioles from in vitro grown plants of interspecific grapevine hybrids cvs `Bianca', `Podarok Magaracha' and `Intervitis Magaracha' were cultured on solid NN medium supplemented with 2,4-D and BA at various concentrations. The callus developed was cultured in liquid NN medium supplemented with 0.5 mg l<sup>–1</sup> BA to induce formation of somatic embryos. Somatic embryos of globular and heart-stage developed in suspensions of `Podarok Magaracha' and `Intervitis Magaracha'. In contrast, `Bianca' did not undergo embryogenesis beyond globular stage. This made it necessary to perform subculture of the suspensions to HTE liquid medium supplemented with 0.2 mg l^–1 BA for the development of globular embryos into heart stage. Heart-stage embryos developed into torpedo-stage after subculturing suspensions of all three cultivars to liquid HTE medium supplemented with 0.1 mg l^–1 IAA and 30 mg l^–1 sodium hummate. Torpedo-stage embryo suspensions were subcultured in liquid HTE medium supplemented with 0.5 mg l^–1 BA, 0.5 mg l^–1 GA₃ and 0.5 mg l^–1 GA₃ + 0.2 mg l^–1 BA. After 12 days of incubation, plantlets were cultured on solid M2MS medium: without growth regulators and with 0.5 mg l^–1 BA. Plantlets that developed in liquid HTE media with 0.5 mg l^–1 GA₃ or 0.5 mg l^–1 GA₃ + 0.2 mg l^–1 BA produced 82–90% shoots on solid M2MS medium with 0.5 mg l^–1 BA after 50 days of culture.     

A facile procedure for efficient plantlet regeneration from self-incompatible hybrids in Antirrhinum

A rapid and efficient regeneration system has been developed for interspecific self-incompatible hybrids between Antirrhinum majus×A. hispanicum. Multiple shoots were induced from hypocotyls explants on Murashige and Skoog medium or Loblolly pine medium supplemented with a low concentration of 3-indoleacetic acid (0.05 mg l^–1) and a high concentration of 6-benzyladenine (1 mg l^–1). Rooting took place in 1/2 Murashige and Skoog medium without growth regulators. By using this procedure, it takes about 5–6 weeks from seed to plantlet. The hypocotyls also had a potential to expand and form callus, providing a source for a continuous supply of multiple shoots from the calli at periodic intervals.     

Plant regeneration via somatic embryogenesis and shoot organogenesis from immature cotyledons of Camellia nitidissima Chi

Camellia nitidissima Chi (Theaceae) is a world-famous economic and ornamental plant with golden-yellow flowers. It has been classified as one of the rarest and most endangered plants in China. Our objective was to induce somatic embryogenesis, shoot organogenesis and plant regeneration for C. nitidissima. Three types of callus (whitish, reddish and yellowish) were induced from immature cotyledons on improved woody plant medium (WPM) with different plant growth regulators (PGRs). Among the callus, whitish callus was induced by 4.5 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and reddish and yellowish callus were induced by strongly active cytokinins, thidiazuron (TDZ) or 6-benzylaminopurine (BAP), singly or combined with weakly active auxin, α-naphthaleneacetic acid (NAA). The embryogenic callus could differentiate into somatic embryos, nodular embryogenic structures (large embryo-like structures) or adventitious shoots depending on the PGR used in WPM. BAP was best for adventitious buds and zeatin was best for somatic embryogenesis while kinetin (Kt) was best for the formation of nodular embryogenic structures. The three regeneration pathways often occurred in the same embryogenic callus clumps. Most shoots (80.0%) developed roots in WPM supplemented with 24.6 μM IBA and 0.3 μM NAA while 47.5% of somatic embryos could germinate directly and develop into plantlets on induction medium supplemented with 0.9 μM BAP and 0.1 μM NAA. The nodular embryogenic structures could be sub-cultured and cyclically developed in one of two differentiation pathways: shoot organogenesis or somatic embryogenesis. Plantlets derived from shoot buds rooted and somatic embryos germinated when transplanted into soil in a greenhouse; 66.7% of plantlets from shoot culture and 78.6% of plantlets from somatic embryos survived after 8 weeks’ acclimatization.     

Plant regeneration from cultured immature embryos and inflorescences ofTriticum aestivum L. (wheat): Evidence for somatic embryogenesis

Summary Tissue cultures ofTriticum aestivum L. (wheat) initiated from young inflorescences and immature embryos possessed the potential for regeneration of whole plants. Both a friable and a compact type of callus were produced on Murashige and Skoog's medium with 2 mg/l 2,4-dichlorophenoxyacetic acid. The friable callus contained meristematic centers in which the peripheral cells ceased dividing, elongated, and could be easily separated. Roots were frequently formed in this type of callus. The compact, yellowish, and nodular callus arose from the epithelial and sub-epithelial cells of the embryo scutellum, and the rachis and glumes of the young inflorescence. Such callus had a smooth surface and characteristic chlorophyllous areas. Plants were regenerated only from the compact callus. The first sign of differentiation in the compact callus was the formation of a cleft or notch on the smooth surface, followed by the appearance of trichomes and the direct development of leafy structures which were not associated initially with any shoot meristems. Multiple shoots subsequently arose at the bases of the leafy structures, which are considered modifications of the scutellum, a definitive part of the cereal embryo. Accordingly, we suggest that while typical bipolar embryos are generally not formed, plant regeneration nevertheless takes place through embryogenesis and the precocious germination of the embryoids. Plants regenerated from immature embryo and inflorescence cultures were grown to maturity in soil, and were shown to have the normal chromosome number of 2n=6x=42.     

Synchronization of somatic embryogenesis from carrot cells at high frequency as a basis for the mass production of embryos

Synchronization of somatic embryogenesis at high frequency is a useful system for the mass production of embryos. Many attempts have been carried out, however, it was difficult to obtain the system in which most of the initial embryogenic cells or cell clusters synchronously differentiate to embryos. In carrot suspension cultures, high frequency, synchronous embryogenesis systems (following three systems) have been established.(1) Small spherical single cells from suspension cultures obtained by sieving and density gradient centrifugation in Percoll solutions differentiated to embryogenic cell clusters at high frequency when they were cultured in a medium containing 2,4-dichlorophenoxyacetic acid (0.05 micromolar), zeatin (1 micromolar) and mannitol (0.2 molar). (2) Embryogenic cell clusters from suspension cultures obtained by sieving, density gradient centrifugation in Ficoll solutions, and subsequent centrifugation at a low speed for a short time synchronously differentiated to embryos, especially globular embryos at high frequency, when they were cultured in a medium containing zeatin (0.1 micromolar) but no auxin. (3) Embryogenic cell clusters obtained by above method are cultured at cell densities of 2×10³ cell clusters ml^-1. Globular embryos which were sieved from embryos induced synchronously differentiated to torpedo-shaped embryos at high frequency when they were cultured at densities below 150 globular embryos ml^-1.Using these systems, the whole process of embryogenesis from single cells to whole plants could be synchronously induced at high frequency.Abbreviations ABA abscissic acid - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellin A₃ - IAA indoleacetic acid - NAA naphthylacetic acid     

A rapid and efficient method for regeneration of plantlets from embryo explants of cumin (Cuminum cyminum)

A new, simple and efficient method was developed for multiple shoot regeneration of cumin from imbibed embryo cultures. This method yielded a large number of shoots within short period of time (30–50 days) without any subculturing. The effects of different media, different embryo explants and various combinations of plant growth regulators (PGRs) on callus formation and shoot regeneration in cumin were investigated. Simultaneous callus formation and shoot regeneration was obtained. The best response for multiple shoot regeneration was observed on B5 medium containing 1.0 mg l^–1 BAP, 0.2 mg l^–1 NAA and 0.4 mg l^–1 IAA, with an average of 140 shoots per explant.