Fertile indica and japonica rice plants regenerated from protoplasts isolated from embryogenic haploid suspension cultures

Summary A system to regenerate fertile rice (Oryza sativa L.) plants (both indica and japonica varieties) from protoplasts isolated from anther-derived embryogenic haploid suspension cultures has been established. Green plants were regenerated from protoplast-derived cell clusters five months after suspension culture initiation. Protoplast yields and subsequent growth of the protoplast-derived microcalli were enhanced by transferring suspension cells into AA medium (Muller et al. 1978) three to four days prior to protoplast isolation. Protoplasts were cultured initially in Kao medium (Kao et al. 1977) and in association with nurse cells for four weeks. Protoplast-derived microcalli were transferred onto N6 (Chu et al. 1975) or MS (Murashige and Skoog 1962) media for callus proliferation. Callus growth was more rapid and the calli were more enbryogenic when grown on N6 medium. The 2,4-D concentration used to develop the suspension culture was important. Cell cultures grown in medium containing 0.5 mg/l 2,4-D released protoplasts whose plating efficiency was higher than for protoplasts obtained from suspension cultures grown in 2.0 mg/l 2,4-D. However, suspension cells grown in 2.0 mg/l 2,4-D were superior with regard to the ability of protoplast-derived calli to regenerate green plants. Amongst several hormone treatments evaluated, a combination of 0.5 mg/l NAA + 5.0 mg/l BAP resulted in the largest number of green plants regenerated. There were no significant differences between BAP or kinetin regarding total number of plants regenerated. More than 200 green plants have been produced form six independently initiated suspension cell lines. The number of regenerated plants per 10⁶ protoplats plated anged from 0.4 to 20.0, and the average seed fertility of single panicles of these R_O plants was about 40%.     

Plant regeneration from protoplasts of durum wheat (Triticum durum Desf. cv. D6962)

Suspension cultures of durum wheat were established from embryogenic callus maintained in liquid medium for 30 months. Protoplasts were readily isolated from the suspension cultures with yields as high as 3 X 10⁷ protoplasts per g fresh weight suspension cells. When incubated in a modified MS medium containing half strength of the macroelements, 5 M 2,4-D (2,4-dichlorophenoxyacetic acid) and 0.6 M glucose, protoplast-derived cells divided at frequencies ranging from 1.4 to 10.0 %. After transfer to a solid subculture medium, the protoplast-derived colonies formed embryogenic protuberances, from which green plants have been regenerated.     

Somatic embryogenesis and fertile green plant regeneration from suspension cell-derived protoplasts of rye (<Emphasis Type="Italic">Secale cereale</Emphasis> L.)

A method for somatic embryogenesis and fertile green plant regeneration from suspension cell-derived protoplasts of rye (Secale cereale L. cv. Auvinen) was developed. Fast-growing and friable embryogenic calli with a high regeneration capacity were induced from immature rye inflorescences using modified MS medium. These friable embryogenic calli were used for suspension culture initiation in liquid AA medium. A high yield of protoplasts was obtained from suspension cell clumps after 3–5 days of subculture. Isolated protoplasts were cultured in KM8p medium. The frequency of protoplast cell divisions and colony formations in liquid culture medium were similar to those on agarose-solidified medium. Compact embryogenic calli were developed from protoplast-derived microcalli in growth medium mMS. Approximately 7% of the transferred embryogenic calli produced green shoots on N₆ regeneration medium. Of 33 green plants, 28 were fertile with normal flowering and seed set. The ratio of green and albino plantlets was 1:4. Rye protoplast-derived green plants showed normal diploid characters as determined by flow cytometer analysis and chromosome counting.Abbreviations 2,4-D 2,4-Dichorophenoxyacetic acid - FDA Fluorescein diacetate - FW Fresh weight - GA₃ Gibberellic acid - Kinetin 6-Furfurylaminopurine - IAA Indole-3-acetic acid - NAA -Naphthaleneacetic acid     

Plant regeneration from protoplasts isolated from suspension cultures of leek (Allium ampeloprasum L.)

A procedure is described for the regeneration of plants from protoplasts of tetraploid leek (Allium ampeloprasum L.), 2n = 4x =32. Regeneration-competent protoplasts could only be obtained from an embryogenic suspension culture that was initiated with friable, embryogenic callus derived from immature embryos. The generally low plating efficiency could be increased by embedding the protoplasts in Ca-alginate, compared to culturing the protoplasts in liquid or agarose-solidified medium. A minimum plating density of 2 × 10⁵ pps/ml was required to obtain microcalli. Upon transfer of the protoplast-derived calli on agarose-solidified BDS medium, morphologically different callus types proliferated. After transfer to regeneration medium, compact or friable calli with an embryogenic appearance produced somatic embryos and plantlets at a frequency of up to 80%. Calli that had been classified as heterogeneous also regenerated shoots, but mainly via organogenesis, at a frequency of 46%. After transfer of shoots to half strength MS medium, healthy, well-rooted plants were obtained, that were successfully transferred to soil. All plants contained the tetraploid DNA level.     

Regeneration of fertile plants from protoplasts derived from embryogenic cell suspensions of barley (Hordeum vulgare L.)

We report regeneration of fertile plants from barley (Hordeum vulgare L. cv. Igri) protoplasts isolated from regenerable suspension cultures initiated from anther-derived embryogenic callus. Plants were routinely regenerated from these suspension cultures, which maintained their regenerative capacity for several months. It was first possible to isolate protoplasts from suspensions after three months of culture and after four months protoplasts capable of division could be isolated. Protoplasts maintained the regenerative capacity of the donor cells and formed embryogenic callus. Green plants were regenerated from protoplast-derived calli, although the proportion of albino plantlets was high. Viable regenerants were transferred to soil and fertile plants were recovered.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 6-BAP 6-benzylaminopurine - PP Protoplasts     

Plant regeneration from protoplasts of a commercial Asian long-grain javanica rice

A reproducible plant regeneration system has been developed for protoplasts from embryogenic cell suspension cultures of the commercial Asian long-grain javanica rice, Oryza sativa cv. Azucena. Protoplasts were isolated routinely from cell suspensions with yields of 5.5–12.0 × 10⁶ g^-1 fresh weight. A membrane filter nurse-culture method was adopted and was essential to support sustained mitotic division of protoplast-derived cells, leading to cell colony formation. The protoplast plating efficiency was higher when suspension cells of Lolium multiflorum, rather than those of the japonica rice O. sativa L. cv. Taipei 309, were employed as nurse cells. A two-step shoot regeneration procedure, in which protoplast-derived calli were cultured initially on medium semi-solidified with 1% (w/v) agarose followed by culture on medium containing 0.4% (w/v) agarose, induced plant regeneration from protoplast-derived calli. Fifteen percent of protoplast-derived tissues regenerated shoots; tissues not subjected to this treatment failed to develop shoots.     

Plant Regeneration from Protoplast of Trititrigia (Triticum sect. trititrigia Maekey)

Trititrigia is the intergeneric hybrid which is from the hybridization between Triticum durum Desf. and Elytrigia intermedium (Host) Nevski. Protoplasts of Trititrigia were isolated from the embryogenic cell suspension derived from immature inflorescence-induced calli of the hybrid F1. The first division occured 48 hr after plating in modified KM8p culture medium. The plating efficiency of protoplasts was 2% and 12.14% when they were cultured in liquid medium and agarose solidified medium, respectively. Clusters grew vigorously under these conditions. Fresh medium with decreased osmoticum was added 20–30 days after plating. When protoplast-derived calli, 2–4 mm in the size, were transferred step by step to different differentiation media, embryoids, green spots emerged and numerous plants regenerated eventually.     

Efficient and stable regeneration from protoplasts of <Emphasis Type="Italic">Cyclamen coum</Emphasis> Miller via somatic embryogenesis

Embryogenic cultures of Cyclamen coum were established on solid media and in suspension, and their growth characteristics in response to different concentrations of plant growth regulators (PGRs) were evaluated. Embryogenic cultures exhibited a high regeneration capacity of 876 somatic embryos per gram fresh mass. Up to 4.24 × 10⁵ protoplasts per gram of fresh mass were isolated from somatic embryos and embryogenic suspension cultures. Protoplasts derived from both embryos and suspension cultures were successfully cultured in vitro and regenerated into plants via somatic embryogenesis. Phenotypic analyses and flow cytometric measurements revealed that some regenerated plants were tetraploid. About 20% of the protoplast-derived calluses used for regeneration were tetraploid, while tetraploidy was found in 0.9% of the plants regenerated from the embryogenic cultures.     

Fertile wheat (Triticum aestivum L.) regenerants from protoplasts of embryogenic suspension culture

We report regeneration of fertile, green plants from wheat (Triticum aestivum L. cv. Aura) protoplasts isolated from an embryogenic suspension initiated from somatic early-embryogenic callus. The present approach combines the optimization of protoplast culture conditions with screening for responsive genotypes. In addition to the dominant effect of the culture media, the increase in fresh mass and the embryogenic potential of somatic callus cultures varied considerably between the various genotypes tested. Establishment of suspension cultures with the required characters for protoplast isolation was improved by reduction of the ratio between cells and medium and by less frequent (monthly) transfer into fresh medium. A new washing solution was introduced to avoid the aggregation of protoplasts. However, the influence of the culture medium on cell division was variable in the different genotypes. We could identify cultures from cultivar Aura that showed approximately a 9% cell division frequency and morphogenic response. The protoplast-derived microcolonies formed both early and late-embryogenic callus on regeneration medium and green fertile plants were obtained through somatic embryogenesis. The reproducibility of plant regeneration from protoplast culture based on the cultivar Aura was demonstrated by several independent experiments. The maintenance of regeneration potential in Aura suspension cultures required establishment of new cultures within a 9-month period.     

Analysis of genetic stability of plants regenerated from suspension cultures and protoplasts of meadow fescue (Festuca pratensis Huds.)

A cytological and molecular analysis was performed to assess the genetic uniformity and true-to-type character of plants regenerated from 20 week-old embryogenic suspension cultures of meadow fescue (Festuca pratensis Huds.), and compared to protoplastderived plants obtained from the same cell suspension. Cytological variation was not observed in a representative sample of plants regenerated directly from the embryogenic suspensions and from protoplasts isolated therefrom. Similarly, no restriction fragment length polymorphisms (RFLPs) were detected in the mitochondrial, plastid and nuclear genomes in the plants analyzed. Randomly amplified polymorphic DNA markers (RAPDs) have been used to characterise molecularly a set of mature meadow fescue plants regenerated from these in vitro cultures. RAPD markers using 18 different short oligonucleotide primers of arbitrary nucleotide sequence in combination with polymerase chain reaction (PCR) allowed the detection of pre-existing polymorphisms in the donor genotypes, but failed to reveal newly generated variation in the protoplast-derived plants compared to their equivalent suspensionculture regenerated materials.The genetic stability of meadow fescue plants regenerated from suspension cultures and protoplasts isolated therefrom and its implications on gene transfer technology for this species are discussed.Abbreviations PCR polymerase chain reaction - RAPD random amplified polymorphic DNA - RFLP restriction fragment length polymorphism.     

Plant Regeneration from Protoplasts Derived from Suspension Cultures in Leymus racemosus

Calli initiated from mature embryos of Leymus racemosus (Lam. Tzvel. =L. giganteus were transferred onto the AA and DM media to produce friable embryogenic callus,from which embryogenic suspension cultures were established. Protoplasts were isolated from the embryogenic suspension cultures and were cultured either in thin-layer liquid medium or in double-layer (agar/liquid) medium. When visible calli were formed they were transferred onto the NBI agar medium or into the MBL liquid medium for further proliferation. These calli were transferred onto differentiation media of NBII and NR, where green spots were developed. Plants with both shoots and roots can be recovered from these green spots on MS Ⅱ medium containing 0.5 mg/L NAA. The results showed that the Km8p basal medium was favourable to the culture of L. racemosus protoplasts during the early stages of culture. In addition, the composition of the media added to the cultures had a marked influence on the growth of protoplasts, indicating that the nutritional requirements in this plant were different at various stages of protoplast growth and differentiation.     

Plant regeneration from protoplasts of wheat (Triticum aestivum cv. Hartog)

Morphologically normal green plants have reproducibly been regenerated from protoplasts of an Australian wheat (Triticum aestivum cv. Hartog). The protoplasts were isolated from fine embryogenic suspension cultures which were initiated from embryogenic callus. Protoplasts were incubated in a modified liquid MS medium containing half strength of the macroelements, 5 m 2,4-D and 0.6 M glucose. Colonies were formed at frequencies ranging from 0.1% to 5%. The frequency of colonies forming fully developed plants varied between 1% and 25%. More than eighty green plants with morphologically normal shoots and roots have been obtained and there was no difficulty in establishing these plants in soil. A cytological study of several randomly selected regenerated plants showed the normal chromosome complement for wheat (2n = 42).     

Fertile plant regeneration from protoplasts of a seed-propagated cultivar of Lilium × formolongi by utilizing meristematic nodular cell clumps

Plant regeneration from protoplasts of Lilium × formolongi cv. Azusa was achieved by utilizing suspension cultures of meristematic nodular cell clumps with a high plant regeneration ability. Creamy-white calli with embryogenic potential were initially induced from the seeds on Murashige and Skoog (MS) medium containing 4.1 μM picloram. The calli were then transferred into a liquid medium of the same composition, in which they turned into compact cell clumps which consisted of meristematic nodules. Protoplasts were readily isolated from these meristematic nodular cell clumps. Colonies were successfully formed from the protoplasts by embedding in 0.1% gellan gum-solidified MS medium containing 4.1 μM picloram and 0.5 M glucose. They regenerated shoots and roots on MS medium containing 2.2 μM benzylaminopurine (BAP). The plants thus obtained produced flowers with normal fertile pollen 8 months after successful transfer into soil. These plants had normal chromosome numbers (2n = 24) but had shorter leaves than original plants. They set seeds after as well as cross pollination.     

REGENERATION OF LIRIODENDRON TULIPIFERA (FAMILY MAGNOLIACEAE) FROM PROTOPLAST CULTURE

Protoplasts were isolated enzymatically from suspension cultures of two embryogenic lines of yellow-poplar (Liriodendron tulipifera L.) and cultured in droplets of a regeneration medium supplemented with 1 mg/1 2,4-D and 0.25 mg/1 6BA and solidified with agarose. Suspension cultures grown in the light yielded substantial numbers of protoplasts, while insignificant numbers were isolated from cultures grown in the dark. The protoplasts reformed cell walls within three days, and 75 percent of them divided at least once within one week in culture. Embryogenic suspension or callus cultures were regenerated by placing agarose droplets containing protoplast-derived microcalli directly into liquid conditioning medium or onto plates of conditioning medium solidified with agar. Embryogenesis was obtained by transferring the callus to a hormone-free induction medium.     

Plant regeneration from embryogenic cell suspensions derived from anther cultures of barley (Hordeum vulgare L.)

Summary We have established embryogenic cell suspension cultures of barley (Hordeum vulgare L. cultivars Igri, Gimpel, Princesse, and Baronesse) from anther-derived embryogenic callus. Suspension cultures of cultivars Igri and Gimpel were regenerable. The most successful cultivar was Igri, from which a number of independent cell lines producing plantlets were established. Plants could be transferred to soil; up to now, 50% of more than 200 regenerated plants were morphologically normal and fertile. The relative frequency of sterile plants increased as suspensions aged. Suspensions older than 1 year produced embryogenic callus but only albino plantlets could be regenerated.     

甘蔗原生质体的植株再生

从甘蔗（Ｓａｃｃｈａｒｕｍ ｏｆｆｉｃｉｎａｒｕｍ Ｌ．）嫩叶外植体诱导愈伤组织,经继代培养后,挑选胚性愈伤组织,转入ＭＳ３ 液体培养基,进行悬浮培养。当培养物分离出小粒状的细胞团,细胞变得小而圆时,用于分离原生质体。原生质体以琼脂糖固化的培养方式培养于ＭＲＰ１ 培养基中。由原生质体再生的愈伤组织有两种类型。挑选粒状、坚实的再生愈伤组织转移到Ｎ６ 分化培养基上,“新台糖１ 号”再生的愈伤组织,在含有ＫＴ ０．５ ｍ ｇ／Ｌ的培养基中,分化出绿芽并长成完整的植株。而“粤糖５７－４２３”和“ＵＳ６６－５６－９”再生的愈伤组织,在加有０．１％ 的活性炭的培养基中,前者分化出白化苗,后者分化出根     

Recovery of somatic embryos and plantlets from protoplast cultures of Larix × eurolepis

Summary Somatic embryos and plantlets were regenerated from protoplasts of hybrid larch (Larix × eurolepis) isolated from two embryogenic callus and cell suspension culture lines (L1 and L2). L2, which was highly embryogenic, consistently yielded protoplasts that gave rise to somatic embryos. Centrifugation on a discontinuous medium/Percoll density gradient resulted in accumulation of embryogenic protoplasts in one of the Percoll interfaces. First division frequencies were in the range of 28–39% in line 1 and 18–20% in line 2 in both liquid and agarose-solidified culture media. The critical factor in maintaining high viability of cultures was lowering of osmotic pressure by dilution of the initial medium. The first somatic embryos were detected in 23- to 28-day-old cultures. Some of these developed into plants that were transferred to soil.     

Regeneration of diploid and tetraploid plants from callus-derived protoplasts of Agapanthus praecox ssp. orientalis (Leighton) Leighton

protoplasts was developed for the Liliaceous ornamental plant, Agapanthus praecox ssp. orientalis (Leighton) Leighton `Royal Purple Select' (2n=2x=32).Viable protoplasts were routinely isolated from leaf-derived embryogenic calluses with yields of 0.8 to 1.5x10 protoplasts per g FW of calluses. Protoplasts started to divide 5 to 7 days after isolation, and protoplast-derived colonies consisting of 50 to 100 cells were obtained after 1 month. A plating efficiency of 0.8% was obtained after 2 months of culture using a gellan gum-solidified medium containing 1 mg 1^-1 each of PIC and BA under continuous illumination. Protoplastderived calluses produced somatic embryos at a frequency of 46.7 % on PGR-free medium, whereas 68.3 % of the calluses regenerated adventitious shoots on a medium containing 1 mg 1^-1 BA. Somatic embryos and adventitious shoots developed into plantlets, which were successfully transplanted to pots. Flow cytometric analysis and chromosome observation revealed that both diploid and tetraploid plants were regenerated from protoplasts.     

Somatic embryogenesis and plant regeneration from embryogenic suspension cultures of perennial ryegrass

Summary Embryogenic callus induced from mature caryopses of perennial ryegrass (Lolium perenne L.) were placed in liquid half-strength Murashige and Skoog (MS) basal medium and supplemented with 6.0 mg/l 2,4-dichlorophenoxy acetic acid (2,4-D), 3 g/l (w/v) casein hydrolysate (CH), and B5 vitamins, to initiate fast-growing highly embryogenic cell suspension cultures. Newly initiated suspension cultures contained a high level of large non-embryogenic cells (NE) with relatively few embryogenic (E) cells. Cell types were separated by discontinuous Percolls gradients or by filtering the newly initiated cultures through 31-μm nylon mesh. The growth conditions of the E cell were optimized by testing various media components including 2,4-D and sucrose, and subculture diluton ratio. Optimal shoot formation occurred after pretreatment of the embryogenic cells on solidified callus maintenance medium supplemented with 60 mg/l cefotaxime for 4 weeks prior to transfer to regeneration medium Regeneration media consisted of half-strength MS basal medium supplemented with B5 vitamins, 0.5 mg/l fluridone, and 0.5 mg/l BA. Most plants regenerated were albino with only a few green plants. Journal Paper number MAES 2959 of the Massachusetts Agricultural Experiment Station.     

Development of an efficient plant regeneration system for Russian wildrye (<Emphasis Type="Italic">Psathyrostachys juncea</Emphasis>)

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is a cool-season forage grass with a broad adaptation to semi-arid regions of North America. In order to explore the potential of biotechnology for genetic improvement of this important forage species, we developed an efficient tissue culture system. Embryogenic calli were induced from mature embryos with an induction frequency in the range of 2-7%. The selected highly embryogenic calli allowed the regeneration of dozens of plants from a single callus. Individual embryogenic calli were then used to establish single genotype-derived suspension cultures. Eighteen embryogenic cell suspension lines were established from three cultivars (Bozoisky-Select, Sawki and Tetracan). A relatively high green plant regeneration frequency, up to 70%, was achieved from plated cell clusters of the established suspension cultures. The regenerated plants were fertile after two winters of vernalization in the field. This efficient plant regeneration system provides a solid basis for generating transgenic plants.