Somatic embryogenesis and plant regeneration in <Emphasis Type="Italic">Catharanthus roseus</Emphasis>

Embryogenic callus in Catharanthus roseus was initiated from hypocotyl on Murashige and Skoog’s (MS) medium supplemented with 1.0–2.0 mg dm⁻³ of 2,4-dichlorophenoxyacetic acid (2,4-D) or chlorophenoxyacetic acid (CPA). Calli from other sources were non-embryogenic. Numerous somatic embryos were induced from primary callus on MS medium suplemented with naphthalene acetic acid (NAA) within two weeks of culture. Embryo proliferation was much faster on medium supplemented with 6-benzylaminopurine (BAP). After transfer to medium with gibberellic acid (GA₃, 1.0 mg dm^{− 3}) mature green embryos were developed and germinated well into plantlets on MS liquid medium supplemented with 0.5 mg dm⁻³ BAP. Later, embryos with cotyledonary leaves were subjected to different auxins treatments for the development of roots. Before transfer ex vitro, plantlets were cultivated on half strength MS medium containing 3 % sucrose and 0.5 mg dm⁻³ BAP for additional 2 weeks. Additionally, the effect of liquid medium has been evaluated at different morphogenetic stages.     

Somatic organogenesis and plant regeneration in <Emphasis Type="Italic">Ricinus communis</Emphasis>

An in vitro propagation system was developed for castor-bean (Ricinus communis L. cv. TMV 6) through cotyledon derived callus cultures. The impact of different concentrations of auxins, cytokinins, additives, amino acids and sugars were evaluated for callus induction and shoot proliferation. Green compact nodular organogenic callus was obtained on the medium fortified with Murashige and Skoog (MS) salts, B5 vitamins, 2.0 mg dm⁻³ 6-benzyladenine and 0.8 mg dm⁻³ α-naphthalene acetic acid (NAA). Multiple shoot proliferation from the callus cultures was achieved on the medium with MS salts, B5 vitamins, 2.5 mg dm⁻³ thidiazuron (TDZ), 0.4 mg dm⁻³ NAA and 15 mg dm⁻³ glutamine. During multiple shoot induction the phenolic secretion was controlled by the addition of 15 mg dm⁻³ polyvinylpyrolidone. The proliferated shoots were elongated on the medium comprising MS salts, B5 vitamins, 1.5 mg dm⁻³ TDZ and 0.3 mg dm⁻³ gibberellic acid. The elongated shoots were rooted on the medium containing MS salts, B5 vitamins, 0.3 mg dm⁻³ indole-3-butyric acid and 0.6 mg dm⁻³ silver nitrate. After root induction, the plants were hardened in earthen pots containing sand, soil and vermiculite.     

<Emphasis Type="Italic">In vitro</Emphasis> propagation of <Emphasis Type="Italic">Ophiorrhiza prostrata</Emphasis> through somatic embryogenesis

In vitro propagation of an anticancerous drug synthesizing plant, Ophiorrhiza prostrata D. Don, was established through indirect somatic embryogenesis. Friable embryogenic calluses were initiated from O. prostrata leaf and internode explants on Murashige and Skoog (MS) media supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) either alone or in combination with N⁶-benzyladenine (BA) or kinetin (KIN). Somatic embryos were developed after subculture of the friable calluses onto half strength MS media containing 0.45 or 2.26 μM 2,4-D alone or in combination with BA or KIN. Medium supplemented with 2.26 μM 2,4-D and 2.22 μM BA was optimal, supporting the production of a mean of 5.8 globular embryos. Subculture of globular embryo-bearing calluses on half strength MS medium without growth regulators produced the highest embryo frequency, and the majority of them developing to early torpedo stage. Somatic embryos underwent maturation and converted to plantlets at high frequency (90 %) on half strength MS medium supplemented with 0.44 μM BA. Somatic embryo-derived plantlets with well-developed roots were established in field conditions with a 90 % survival rate.     

Plant regeneration from <Emphasis Type="Italic">Gossypium davidsonii</Emphasis> protoplasts <Emphasis Type="Italic">via</Emphasis> somatic embryogenesis

Protoplasts isolated from wild cotton Gossypium davidsonii were cultured in KM₈P medium supplemented with different phytohormones. The most effective combination was 0.45 μM 2,4-dichlorophenoxyacetic acid, 2.68 μM α-naphthaleneacetic acid and 0.93 μM kinetin and the division percentage at the 8^th day was 30.78 ± 3.04 %. The density of protoplasts at 2–10 × 10⁵ cm⁻³ was suitable for protoplast division and calli formation, with a division percentage of 32.21 ± 3.64 % and a plating efficiency of 9.12 ± 2.61 % at the 40^th day. The optimal osmotic potential was achieved using 0.5 M glucose or 0.1 M glucose plus 0.5 M mannitol. Protoplasts were cultured in three ways, a double-layer culture system, with liquid over solid medium was proved to be the best way. Embryo induction was further increased by addition of 0.14 μM gibberellic acid.     

Direct shoot organogenesis from needles of three genotypes of <Emphasis Type="Italic">Sequoia sempervirens</Emphasis>

Using in vitro-grown needles of Sequoia sempervirens (D. Don.) Endl., direct shoot organogenesis was induced. The effects of three genotypes and two cytokinins, N⁶-benzyladenine (BA) and N-benzyl-9 (2-tetrahydropyranl) adenine (BPA), in combination with 2,4-D were investigated. Among tested cytokinins, BPA produced the highest frequency of shoot organogenesis from all three genotypes tested. Adventitious shoots were induced directly from explants without intervening callus within 5weeks following incubation. Shoots were elongated on a 1/2 Wolter and Skoog (WS) medium supplemented with activated charcoal but without growth regulators. Later, elongated shoots were transferred to a 1/4 WS medium, but without activated charcoal and free of plant growth regulators to promote continued shoot growth. These shoots rooted spontaneously.     

Somatic embryogenesis and plant regeneration of <Emphasis Type="Italic">Abelmoschus esculentus</Emphasis> through suspension culture

A simple and reliable protocol for regeneration of okra through somatic embryogenesis from suspension cultures has been developed. Embryogenic callus was obtained from hypocotyl explants cultured on media with Murashige and Skoog (MS) salts, Gamborg (B5) vitamins, 2.0 mg dm⁻³ 2,4-dichlorophenoxyacetic acid (2,4-D), 1.0 mg dm⁻³ naphthaleneacetic acid (NAA), 25 mg dm⁻³ polyvinylpyrrolidone and 30 g dm⁻³ sucrose. More number and high frequency of healthy embryoids appeared individually in suspension culture containing MS salts, B5 vitamins, 2.0 mg dm⁻³ 2,4-D and 1.0 mg dm⁻³ kinetin. Formation of cell clusters from the single cells was clearly noticed during ontogeny. Matured embryos at the cotyledonary stage were transferred to agar solidified medium for germination. The best conversion of embrya into plantlets (67.3 %) was recorded on media with half strength MS salts, B5 vitamins, 0.2 mg dm⁻³ benzylaminopurine (BAP) and 0.2 mg dm⁻³ gibberellic acid (GA₃). The plantlets were transferred to soil and hardened in the plastic pots. After proper acclimatization, the plantlets regenerated through somatic embryogenesis were compared to seed grown plants to observe any variation.     

Micropropagation of <Emphasis Type="Italic">Harpagophytum procumbens</Emphasis>

An efficient protocol for micropropagation of Harpagophytum procumbens DC., an endangered African medicinal plant, was developed. Maximum shoot multiplication without callus was obtained from nodal explants cultured on Murashige and Skoog (MS) basal salts plus Gamborg’s (B₅) vitamins supplemented with 0.1 mg dm⁻³ indole-3-acetic acid and 5.0 mg dm⁻³ kinetin. The shoots were subsequently subcultured every 3 weeks on the same medium. Detached axillary shoots were transferred to MS basal salts plus B₅ vitamins supplemented with various concentrations of α-naphthalene-acetic acid or indole-3-butyric acid (IBA), ranging from 0.5 to 2.5 mg dm⁻³ and 100 % rooting and optimal subsequent acclimatization was achieved on 1.0 mg dm⁻³ IBA. After 4 weeks of culture, the rooted shoots (>5 cm) were planted in pots containing peat, vermiculite and bark (2:1:1), covered with plastic domes and maintained at 25 °C for 2 weeks before being transferred to a glasshouse. Plant survival was about 40 %.     

Plantlet regeneration from fascicular buds of seedling shoot apices of <Emphasis Type="Italic">Pinus roxburghii</Emphasis> Sarg

Shoot apices of Pinus roxburghii Sarg were cultured on Murashige and Skoog’s medium (MS) supplemented with cytokinins [6-benzyladenine (BA), kinetin and N-benzyl-9-(2-tetrahydropyranyl) adenine (BPA)] alone and in combination with auxin, α-napthaleneacetic acid (NAA). Of the three cytokinins tested at varying concentrations, medium supplemented with 10 μM BA was found optimal in respect of explant responsiveness (97.22 %) and average number of buds induced per explant (7.42). The concentration of cytokinins in the induction medium had a profound effect on rate of elongation of induced buds on MS basal medium containing 0.5 % activated charcoal. Further, shoots induced on lower concentrations of BA increased up to 2.4 times in length in 4 weeks. Decapitation of the explant enhanced the rate of axillary bud elongation. Proliferating shoot cultures were established by sub-culturing the axillary shoots on MS supplemented with 10 μM BA. Shoots 2–3 cm in length were suitable for culturing as more buds were induced on them compared to longer or shorter shoots. Root primordia were induced on 70.83 % shoots when transferred to 1/2 MS medium supplemented with 5.0 μM NAA. Elongation of root primordia (60 %) was achieved in liquid 1/2 MS basal medium. The plantlets were successfully transferred to soil after hardening; the time period from initiation of shoot buds to transplantation being 20–22 weeks.     

Estimation of endogenous contents of phytohormones during internode development in <Emphasis Type="Italic">Merremia emarginata</Emphasis>

During the entire period of internode growth of Merremia emarginata contents of gibberellic acid (GA₃), phenyl-acetic acid (PAA), indole-3-acetic acid (IAA, free and conjugated) and abscisic acid (ABA, free and conjugated) were estimated by ELISA using polyclonal antibodies raised against each hormones. At the time of internode elongation free auxin content was low and increased with the decrease in the rate of elongation. In contrast, conjugated IAA showed declining trend where free IAA content was remarkably high, suggesting thereby that conjugated IAA might have mobilized during the later phase of internode development. The endogenous GA₃ contents were high as compared to other hormones; however, no significant role of GA₃ was discernible in elongation growth. Conjugated ABA contents remained very low during the elongation growth and increased thereafter.     

Effect of growth regulators and ethylmethane sulphonate on growth,and chlorophyll,sugar and proline contents in <Emphasis Type="Italic">Dracaena sanderiana</Emphasis> cultured <Emphasis Type="Italic">in vitro</Emphasis>

A high efficient four step protocol (callus initiation, regeneration, shoot elongation and rooting) for in vitro propagation of Dracaena sanderiana Sander ex Mast was developed. Callusing was achieved from nodal stem segment explants treated with various concentrations of ethylmethane sulphonate (EMS) on MS medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D; 1.5 g m⁻³). A significant increase in callus induction percentage and biomass production was noticed from lower EMS treated lines (ET₁ and ET₂) comparatively to control and other (ET₃, ET₄ and ET₅) lines. Calli of ET₁ line showed high regeneration potential on MS medium with N ⁶-benzylaminopurine (BAP; 1.75 g m⁻³). Length of microshoots, which was reduced by EMS, restored by addition of gibberellic acid (GA₃; 0.4 g m⁻³). A marked increase in rooting with increasing EMS concentration was noticed on MS medium fortified with 3-indolebutyric acid (IBA; 1.5 g m⁻³).     

Efficient regeneration of <Emphasis Type="Italic">Eucommia ulmoides</Emphasis> from hypocotyl explant

A rapid and efficient method for the regeneration of Eucommia ulmoides Oliver has been developed. The ability of hypocotyl segments to produce adventitious buds varied depending upon their position, seedling age and culture medium. The most adventitious buds were induced from the hypocotyl segments near to the root of 2-week-old seedlings on the Murashige and Skoog (MS) basal medium supplemented with 10 μM benzylaminopurine (BAP). However, the MS medium with 6 μM BAP and 6 μM gibberellic acid (GA₃) was most suitable for shoot multiplication and further growth. Shoots longer than 2 cm cultured on the half-strength MS medium supplemented with 0.5 μM naphthaleneacetic acid (NAA) produced a maximum number of roots per shoot. Regenerated plantlets could be successfully acclimatized.     

Cryopreservation of <Emphasis Type="Italic">Robinia</Emphasis><Emphasis Type="Italic">pseudoacacia</Emphasis>

Cryopreservation of Robinia pseudoacacia explants by vitrification achieved 78% survival following the stepwise preculture of shoot tips in (0.3 + 0.5 + 0.7 M) sucrose with a 80 min incubation in PVS2; compared to 87% survival after desiccation of explants to 30% water content, following 3 days alginate bead (with glycerol and sucrose treatments) preculture in 0.7 M sucrose.     

Development of <Emphasis Type="Italic">in vitro</Emphasis> methods for <Emphasis Type="Italic">ex situ</Emphasis> conservation of <Emphasis Type="Italic">Eucalyptus impensa</Emphasis>, an endangered mallee from southwest Western Australia

A method is described for in vitro propagation of the critically endangered ‘Eneabba mallee’ (Eucalyptus impensa) from southwest Western Australia. Half-strength MS medium supplemented with 0.25 μM 6-benzylaminopurine and 2.5 μM kinetin resulted in the best combination of shoot multiplication and shoot quality compared to other treatments. Shoots of this species tended to be very compact under in vitro conditions. Shoot length was significantly enhanced with the addition of 0.5 or 1.0 μM gibberellic acid (A₄ isomer) when compared to basal medium (no hormone supplements) or basal medium containing only cytokinin (0.5 μM zeatin). Up to 97.0 ± 3.0% of shoots produced roots on 1/2 MS medium supplemented with a combination of 5 μM indolebutyric acid and 0.5 μM α-naphthaleneacetic acid. Over 70% of shoots transferred to potting mixture remained viable after 3 months. This study has significantly progressed ex situ conservation initiatives for Eucalyptus impensa.     

Somatic embryogenesis from zygotic embryos of <Emphasis Type="Italic">Schisandra chinensis</Emphasis>

We describe the multi-step regeneration system of medicinal plant Schisandra chinensis (Turcz.) Baill. The seeds were pre-treated with 0.005 μM thidiazuron. Subsequently the zygotic embryos of the early heart stage were cultured on medium with 50 μM of 2,4-dichlorophenoxyacetic acid (2,4-D) and after three weeks the embryogenic calli were transferred to a medium with 10 μM of 2,4-D and 4 μM of 6-benzyladenine and were sub-cultured at the 4-week intervals. Abscisic acid (30 μM) and polyethyleneglycol (3 %) significantly influenced the synchronization of development of the somatic embryos (SEs) to the globular stage. The following culture on a medium without growth regulators resulted in full developed cotyledonary stage SEs. Indole-3-butyric acid (0.05 μ) contributed to their rapid conversion to plantlets.This experimental work was supported by project No. 521/02/1129 of the Grant Agency of the Czech Republic.     

Transformation of pollen embryo-derived explants by <Emphasis Type="Italic">Agrobacterium tumefaciens</Emphasis> in <Emphasis Type="Italic">Hyoscyamus niger</Emphasis>

Leaf, root, stem, petiole, hypocotyl, and zygotic embryo explants, as well as pollen embryoids, and redifferentiated tissues from pollen embryoid-derived plantlets of Hyoscyamus niger L. (black henbane) were inoculated with Agrobacterium tumefaciens, harboring binary vectors (pGS Gluc1) and then cultured on media containing kanamycin. Transient -glucuronidase activity and kanamycin resistant callus formation were influenced by explant origin. Transgenic calluses were obtained at a frequency of up to 30% from all the explants tested. However, transgenic shoots were obtained only from the hypocotyl of plantlets derived from pollen embryoids. Transformation was confirmed by the ability of leaf segments to produce kanamycin resistant calluses, -glucuronidase histochemical and flurometric assays, polymerase chain reaction and Southern blot analysis. The results show that pollen embryoid-derived explants may be an alternative source for both efficient transformation and regeneration of transgenic plants in recalcitrant species.     

<Emphasis Type="Italic">In vitro</Emphasis> regeneration of medicinal plant <Emphasis Type="Italic">Centella asiatica</Emphasis>

This paper describes multiple shoot regeneration from leaf and nodal segments of a medicinally important herb Centella asiatica L. on Murashige and Skoog’s (MS) medium supplemented with a range of growth regulators. The highest number of multiple shoots was observed on MS augmented with 3.0 mg dm⁻³ N⁶-benzylaminopurine (BAP) and 0.05 mg dm⁻³ α-naphthaleneacetic acid (NAA). Leaf explant showed maximum percentage of cultures regenerating shoots (81.6 %), with the highest shoot number (8.3 shoots per explant) and the shoot length (2.1 cm) whereas, nodal explant showed less number of shoots with callus formation at the base cut end. Successive shoot cultures were established by repeatedly sub-culturing the original explant on a fresh medium. Rooting of in vitro raised shoots was best induced on half strength MS supplemented with 0.5 mg dm⁻³ indole-3-butyric acid (IBA) with highest percentage of shoot regenerating roots (76.8 %) with 3–4 roots per shoot. Plantlets were acclimated in Vermi-compost and eventually established in soil. Contents of chlorophyll, total sugars, reducing sugars and proteins were estimated in leaf tissue from both in vivo and in vitro raised plants. Chlorophyll content was higher in in vivo plants, whereas other three components were higher in in vitro plants.     

<Emphasis Type="Italic">Narcissus</Emphasis> bulblet formation <Emphasis Type="Italic">in vitro</Emphasis>: effects of carbohydrate type and osmolarity of the culture medium

Shoot clump cultures of Narcissus cultivars St. Keverne and Hawera were used to investigate the effects of culture medium carbon supply, type of carbohydrate and osmolarity on in vitro bulblet development. Increasing the medium osmolarity using mannitol or sorbitol, which did not act as substrates for growth, failed to stimulate bulblet formation with either cultivar. An exception to this was a relatively small increase in total bulblet dry weight per culture, in the cultivar Hawera only, caused by adding 30 g l ^–1 sorbitol in combination with 30 g l^–1 sucrose. Simultaneously increasing the medium osmolarity and carbon supply using the metabolisable carbohydrate sources, sucrose, glucose, fructose or an equimolar mixture of glucose and fructose stimulated bulblet production, total dry matter accumulation and partitioning into bulblets. At comparable levels of carbon supply up to 19.0 g l^–1, bulblet development of both cultivars was similar with monosaccharide and sucrose media. This indicates that substrate supply is more important for bulblet development than osmolarity of the culture medium. The cultivar Hawera also showed similar responses to monosaccharide and sucrose media supplying 37.9 g C l^–1, despite the high osmolarity of monosaccharide media (c. 650 m Osm kg^–1, equivalent to –1.6 MPa, compared to 380 m Osm kg^–1 for sucrose medium). However in St. Keverne total dry matter accumulation and dry weight per bulblet were further stimulated only by increasing the sucrose supply from 19.0 to 37.9 g C l^–1, not by increasing the monosaccharide supply. Implications of the findings for Narcissus micropropagation are discussed.     

Enhanced induction of microspore embryogenesis after <Emphasis Type="Italic">n</Emphasis>-butanol treatment in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) anther culture

The aim of this study was the improvement of embryo production in wheat anther culture. Three butanol alcohols, n-butanol, sec-butanol and tert-butanol, were evaluated for their effect on microspore embryogenesis in two spring cultivars of wheat, Pavon and Caramba. Application of n-butanol, at 0.1 and 0.2% (v/v) in the induction media for 5 h, highly improved embryo production in both cultivars. Sec- and tert-butanol performed similarly to control plates. Regeneration ability was unaffected by any butyl-alcohol treatment. As a consequence of the higher embryo production after n-butanol treatment, the number of green regenerated plants increased up to five times in cultivar Pavon and up to three times in cultivar Caramba. The percentage of green plants was improved or unaffected by the treatment. Doubled haploid plant production was between 2 and 4 times higher after n-butanol treatment than in control plates. Therefore, n-butanol was successfully applied in the production of wheat doubled haploids. This primary alcohol is known as an activator of phospholipase D and has been previously reported to disrupt cortical microtubules and detach them from the plasma membrane in plants. Its effects on androgenetic induction could confirm the importance of microtubule regulation in plant cell fate, specifically in microspore development. A possible implication of phospholipase D is discussed.     

<Emphasis Type="Italic">In vitro</Emphasis> plant regeneration from the immature seeds of <Emphasis Type="Italic">Cymbidium faberi</Emphasis>

An in vitro plant regeneration protocol of Cymbidium faberi from immature seeds was established. The immature seeds of 50 days old started to form rhizomes 4 months after they were cultured on hormone free medium. The rhizomes multiplied 5 times when subcultured on the medium containing 1.0 mg l^–1 -naphthalene acetic acid (NAA) for 40 days and more than 90% of the rhizomes initiated shoots within 60 days on the media containing 0.5 or 1.0 mg l^–1 NAA plus 2.0 or 5.0 mg l^–1N⁶-benzylaminopurine (BA). Plantlets were regenerated when the shoots were planted on the basal medium amended with 1 g l^–1 activated charcoal for 50 days and the plantlets grew normally after transplanting.     

Pro-embryos induction from <Emphasis Type="Italic">Olea europaea</Emphasis> L. isolated microspore culture

Studies were undertaken with one olive (Olea europaea L.) cultivar to identify buds with microspores competent to embryogenesis in vitro. Isolated microspore cultures were performed for the induction of gametic embryogenesis. Different pollen development stages and stress conditions (heat or cold shock) were evaluated. The correlation of inflorescence, anther morphology and the suitable stage of microspore development were analysed. The morphology of responsive buds was identified which corresponded with microspores from the late uni-nucleate to early bi-nucleate pollen stages. Symmetrical divisions of microspores as well as resulting multinucleate structures and pro-embryos were observed. In this paper, a new method of isolated microspore culture that leads to cell division and pro-embryos in olive, is reported.