Efficient production of doubled haploid plants through colchicine treatment of anther-derived maize callus

Summary A chromosome doubling technique, involving colchicine treatment of an embryogenic, haploid callus line of maize (Zea mays L., derived through anther culture), was evaluated. Two colchicine levels (0.025% and 0.05%) and three treatment durations (24, 48, and 72 h) were used and compared to untreated controls. Chromosome counts and seed recovery from regenerated plants were determined. No doubled haploid plants were regenerated from calli without colchicine treatment. After treatment with colchicine for 24 h, the callus tissue regenerated about 50% doubled haploid plants. All of the plants regenerated from the calli treated with colchicine for 72 h were doubled haploids, except for a few tetraploid plants. No significant difference in chromosome doubling was observed between the two colchicine levels. Most of the doubled haploid plants produced viable pollen and a total of 107 of 136 doubled haploid plants produced from 1 to 256 seeds. Less extensive studies with two other genotypes gave similar results. These results demonstrate that colchicine treatment of haploid callus tissue can be a very effective and relatively easy method of obtaining a high frequency of doubled haploid plants through anther culture.     

Anther Culture of Naked Oat and the Establishment of Its Haploid Suspension Cell

This paper reported the production of haploid plants through anther culture in naked oat (Arena nuda). Calluses were induced from anthers of naked oat placed on various culture media. MS medium with 4% sucrose, 1% activated charcoal and no hormones gave the highest initiation frequencies (14.7%) of anther callus among media tested. Twelve green plants and one albino plant have been regenerated from anther calluses. Cytological examination of mitotic rooot tip ceils from three green anther plants showed that two of the plants were haploid (2n=3x=21) and one was diploid (2n=6x=42). The cell suspension cultures were established from pollen friable calluses in liquid medium. The suspension cells were cytologically stable during one year subcultures. Most of the ceils examined were haploid.     

Microscopical Observations on the Embryoid Formation in Cultured Unfertilized Ovules of Helianthus annuus L.

A recent advance in plant experimental embryology is the induction of haploid plants via in vitro culture of unfertilized ovules. Using float culture method on liquid media, we have raised haploid as well as diploid embryoids in sunflower cultivars by ovule culture. The present investigation was aimed to know the origin and developmental processes of these embryoids. Young flowers 1–4 days before anthesis were dissected and ovules were inoculated on N6 medium supplemented with 0.5–2 ppm MCPA and 6% sucrose. During culture period, samples were collected at intervals, fixed, stained and sectioned by paraffin method. Fifty one gynogenie embryoids of various sizes were observed among Ca. 2000 ovules. They were located at the micropylar end of the embryo sacs and proved to be originated from the unfertilized egg cells. At the early stages, they bore a strong resemblance to the zygotic proembryos in vivo, but after a considerable enlargement, they grew into globular, ovoid or elongated big bodies without polarized organ differentiation. Chromosome counts on some mitotic figures in these embyoids revealed their haploid nature. Embryoids were also produced from the endothelial tissue, which proliferated markedly after inoculation, especially at the chalazal parts, resulting in massive multilayered irregular folds and then degenerated. In some eases, cell divisions at one or several places led to embryoid or callus formation. The problems of how to regulate the growth of in vitro ovules in order to promote the gynogenic embryoids and inhibit the somatic embryoids or calli are left for future research.     

Efficient protocol for in vitro production of androgenic haploids of <Emphasis Type="Italic">Phlox drummondii</Emphasis>

Production of haploid plants has been restricted to only a few ornamental species. In this paper an efficient anther culture protocol has been devised for production of haploid plants of Phlox drummondii, a garden ornamental. Anthers with microspores at early- to late-uninucleate stages were inoculated on MS (Murashige and Skoog, Physiol Plant 15:473–479, 1962) basal medium containing 9% sucrose, 10 μM 2,4-D + 5 μM BA in the dark for callus induction. The callus (~2 mm) was transferred to MS medium containing 3% sucrose + 10 μM BA + 5 μM NAA under a 16 h photoperiod for multiplication. Anther-derived callus showed the greatest shoot differentiation (60% with greater than 3 shoots per culture) at 13 weeks after culture initiation when maintained on MS medium supplemented with 3% sucrose and cytokinin (7.5 μM BA). At 68 weeks, only 4.6% of cultures differentiated with less than one shoot per callus. Anther-derived shoots rooted readily on MS medium containing 7.5 μM IAA. Of 60 plants that regenerated from anther callus, 50% were haploid, 30% diploid, and 20% aneuploid. Developed protocol could be useful for the haploid induction of outcrossing ornamental plants for production of their homozygous double haploids.     

Anther culture of maize and the visualization of embryogenic microspores by fluorescent microscopy

Summary Three maize genotypes previously shown in the literature to respond to anther culture were tested under various conditions. Studies indicated that embryogenic response ranged from 0 to 100 embryos per 1,000 anthers plated and was significantly lower without cold pretreatment of the anthers. Culture in liquid media tended to produce more embryos than in semi-solid as did the addition of activated charcoal to either liquid or solid culture media. Most results were confounded by plant-to-plant variation which tended to obscure significant differences. In one study, germination rate of androgenetic embryos averaged about 20%, but only 26% of those embryos that germinated completed their reproductive cycle and formed seed albeit through sibpollination since plants could not be selfed. Chromosome counts using root tip squashes indicated that regenerated plants were either haploid or diploid but plants scored as non-diploid yielded as much seed as scored diploids. This suggests that progeny can be recovered even from putative haploids, presumably as a result of sectoring in the developing ear. A DNA-specific fluorescent dye was used to visualize the presence of putative embryogenic microspores (PEMs) during the culture period. PEM counts were a function of time in culture and were apparently greater than the number of embryos obtained for a given treatment. The data indicate that, as previously reported for other species, both induction and survival phases also exist in maize anther culture.     

Histological study of somatic embryogenesis induction on zygotic embryos of macaw palm (<Emphasis Type="Italic">Acrocomia aculeata</Emphasis> (Jacq.) Lodd. ex Martius)

The aim of this paper was to describe the histological events that led to somatic embryogenesis in macaw palm (Acrocomia aculeata (Jacq.) Lodd. ex Martius). Zygotic embryos were inoculated on Y₃ medium containing 9 μM 4-amino-3,5,6-trichloropicolonic acid (picloram). Somatic embryos regenerated from nodular callus on induction medium with activated charcoal under photoperiod or without activated charcoal under dark. Many proembryos originated from the fundamental meristem after 10–20 days of culture. When transferred to medium containing activated charcoal, under photoperiod, calli regenerated into somatic embryos of unicellular origin. These embryos had protoderm, plumule and procambial strands and some of them could germinate. After 30–40 days of culture, meristematic masses grew from procambial cells. The masses generated nodular callus, and after transfer to medium without activated charcoal, under dark, they generated somatic embryos of multicellular origin. Those embryos did not regenerate into plants.     

Phenotypic and cytological variation among plants derived from anther cultures ofLilium longiflorum

Summary Anther culture of the Easter Lily (Lilium longiflorum; 2n=2x=24) was attempted in order to evaluate its potential in generating haploids for the production of hybrid cultivars. The effects of genotype, temperature (low temperature treatment of buds and high temperature treatment of cultures), sucrose concentration and growth regulators were tested. The most important factors for callus induction were the genotype and the presence of 2,4-dichlorophenoxyacetic acid. Pre-treatments at low or high temperature had no apparent effect, while high sucrose concentration was inhibitory. Callus was derived from 28 of the 108 genotypes tested and plants were regenerated. Phenotypic variations were observed among these regenerants. Somatic chromosome numbers were determined in 42 plants derived from 10 donor genotypes. Thirteen plants were diploid and 29 were mixoploid with chromosome numbers ranging from 11 to 26. Four of the mixoploid plants had a high proportion of cells with haploid chromosome numbers, particularly at early stages of development. Meiosis was examined in plants with flower buds. Most plants had 12 bivalents at Metaphase I, but also aneuploids were observed. Other irregularities included bridges and laggards at Anaphase I. The occurrence of high frequencies of haploid cells (up to 80%) in root tips suggests that some plants may be of gametic origin. Research was supported by the Easter Lily Research Foundation, the Ohio Floriculture Foundation, the Gloeckner Foundation and the Oregon Agricultural Experiment Station (technical paper no. 8398).     

Influence of physical conditions of nutrient medium and sucrose on somatic embryogenesis of date palm

Shoot tips and leafy bud fragments removed from offshoots of adult date palms (Phoenix dactylifera L.) were cultured on a nutrient medium containing the Murashige and Skoog inorganic salts, 453 M 2,4-dichlorophenoxyacetic acid, 14.8 M N⁶-(2-isopentenyl)adenine and 3 g l^-1 activated charcoal to develop nodular callus after 8 months of culture. Callus was cultured in agar-solidified and stationary or shaken liquid media containing half-strength MS inorganic salts, 3 g l^-1 activated charcoal and different sucrose concentrations to study the influence of these factors on somatic embryogenesis. The best conditions for embryo development were culturing in liquid medium shaken at 100 rpm for a period of 2 weeks without sucrose, followed by culture on 3% sucrose.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 2iP N⁶-(2-isopentenyl) adenine - MS Murashige & Skoog (1962) - rpm revolutions per minute     

Effect of genotype and season on gynogenesis efficiency in Gerbera

The effects of season, genotype and their interaction on haploid production were evaluated on four genotypes responsive to gynogenesis. Naked mature unfertilised ovules, collected from April to October, were cultivated on modified MS basal medium plus 0.88 μM 6-benzyladenine and 0.57 μM indol-3-acetic acid. After 30–60 days, recovered calli were transferred to a MS basal medium with 8.8 μM BA and 0.57 μM IAA for regeneration. Genotype and season of ovule collection substantially interact in the recovery of haploid calli. Between the four genotypes analysed, two gave more calli in the spring, one in the autumn and the fourth showed only weak differences between seasons. Shoot recovery depended upon both the season of ovule collection and the genotype but no significant interaction was shown by our data. The ability to produce haploid callus is not predictive for efficient shoot regeneration. This revised version was published online in June 2006 with corrections to the Cover Date.     

A continuous culture system of direct somatic embryogenesis in microspore-derived embryos of Brassica juncea

Summary An efficient culture system has been developed for repeated cycles of somatic embryogenesis in microspore-derived embryos of Brassica juncea without a callus phase. Haploid embryos produced through anther culture showed a high propensity for direct production of somatic embryos in response to 2 mgL^–1 BA and 0.1 mgL^–1 NAA. The embryogenic cultures which comprised the elongated embryonal axis of microspore-derived embryos when explanted and grown on the medium of same composition produced a large number of secondary embryos. These somatic embryos in turn underwent axis elongation and produced more somatic embryos when explanted and cultured. This cycle of repetitive somatic embryogenesis continued with undiminished vigour passage after passage and was monitored for more than a year. Somatic embryos from any passage when isolated at cotyledonary stage and grown on auxin-free medium for 5 days and then on a medium containing NAA (0.1 mgL^–1), developed into complete plants with a profuse root system and were easily established in the soil. The cytology of the root tips of these plants confirmed their haploid nature. The total absence of callus phase makes the system ideal for continuous cloning of androgenic lines, Agrobacterium-mediated transformation and mutation induction studies.     

Successful development of a shed-microspore culture protocol for doubled haploid production in Indonesian hot pepper (Capsicum annuum L.)

Various systems of anther and microspore cultures were studied to establish an efficient doubled haploid production method for Indonesian hot pepper (Capsicum annuum L.). A shed-microspore culture protocol was developed which outperformed all the previously reported methods of haploid production in pepper. The critical factors of the protocol are: selection of flower buds with more than 50% late unicellular microspores, a 1 day 4°C pretreatment of the buds, followed by culture of the anthers in double-layer medium system for 1 week at 9°C and thereafter at 28°C in continuous darkness. The medium contained Nitsch components and 2% maltose, with 1% activated charcoal in the solid under layer and 2.5 μM zeatin and 5 μM indole-3-acetic acid in the liquid upper layer. All the ten genotypes of hot pepper tested, responded to this protocol. The best genotypes produced four to seven plants per original flower bud. This protocol can be used as a potential tool for producing doubled haploid plants for hot pepper breeding.     

Haploid plant regeneration via embryogenesis from anther cultures of Hepatica nobilis

An anther culture technique for the production of haploid plants was developed in Hepatica nobilis. Embryos with bipolar meristem regions were induced from microspores within the cultured anthers. Embryo formation was promoted by first culturing anthers on NN medium (Nitsch and Nitsch, 1969) supplemented with 1% activated charcoal (AC) at 5 or 35?°C for a few days and by then incubating them in the dark at 25?°C. Pre-culturing anthers at 35?°C for 4?days (thermal-shock treatment) led to the best embryo formation (45 embryos/Petri dish with 30 anthers). Plant regeneration was achieved by culturing the anther-derived embryos on NN medium without AC at 15?°C. Flow cytometric analysis of anther-derived embryos and chromosome counts in regenerated plants showed that they were haploid plants.     

Somatic embryogenesis and plant regeneration from cell suspension cultures of Cucumis sativus L.

A procedure for the regeneration of whole cucumber plants (Cucumis sativus L. cv. Poinsett 76) by embryogenesis from cell suspension cultures is described. Embryogenic callus was initiated from the primary leaves of 14–17 day old plants. Suspension cultures of embryogenic cells were grown in liquid Murashige and Skoog basal medium containing 5 uM 2,4,5-trichlorophenoxyacetic acid and 4 uM 6-benzylaminopurine. Suspension cultures were composed of a population of cells that were densely cytoplasmic and potentially embryogenic. Differentiation of embryos was enhanced by washing the suspension culture cells with MS basal medium containing 0.5% activated charcoal and twice with MS basal medium followed by liquid shake cultures in MS basal medium. Sixty to 70 percent of the embryos prewashed with activated charcoal germinated into plantlets with normal morphology. Embryos obtained from suspension cultured cells without prewashing with activated charcoal organized into plantlets with abnormal primary leaves. Morphologically normal plantlets were obtained by excising the shoot tips and transferring them to fresh medium.Abbreviation BAP 6-benzylaminopurine - 2,4,5-T 2,4,5-trichlorophenoxyacetic acid - MS Murashige and Skoog     

Haploid plants from in vitro anther culture of the leguminous tree,Peltophorum pterocarpum (DC) K. Hayne (Copper pod)

The development of haploid callus, embryos and plantlets from cultured anthers and the various factors affecting androgenesis in Peltophorum pterocarpum (Copper pod), a tropical legume tree is reported. A pretreatment of flower buds at moderate temperature of 14°C for 8 days was most effective for callus production. The colour of the anther was found to be a reliable and efficient indicator for identification of suitable stage of anther for culture. The frequency of anthers which produced callus and shoots was highest when anthers were cultured at mid or late-uninucleate stage. A high sucrose concentration of 10% is a specific media requirement for androgenesis. The haploid nature of the embryos, callus and regenerated plants (n=14) were confirmed by chromosome count.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - KN kinetin - NAA naphthaleneacetic acid - BAP bezylaminopurine     

Culture and fusion of pollen protoplasts of Brassica oleracea L. var. italica with haploid mesophyll protoplasts of B. rapa L. ssp. pekinensis

Hybrid callus was formed from the successful protoplast fusion between pollen protoplasts of Brassica oleracea var. italica and haploid mesophyll protoplasts of Brassica rapa. The pollen protoplast isolation frequency in broccoli was highly related to the ratio of trinucleate pollens in the male gametophyte population. Large quantities of pollen protoplasts with high vigor could be isolated, and the isolation frequency reached up to 90% in 6.0-7.0 mm long flower buds with about 94.7% trinucleate-stage pollens. Pollen protoplasts could be collected and purified by discontinuous gradient centrifugation. In 1% Na-alginate embedding culture, cell divisions were observed but no further development was found. The haploid mesophyll protoplasts were isolated from in vitro haploid plants of B. rapa. Results strongly showed the variability in culturability of mesophyll protoplasts from different haploid lines. Both pollen protoplasts and haploid mesophyll protoplasts retained a stable round shape in the designed prefusion solution with an osmotic pressure of 0.74 osmol/kg. Polyethylene glycol was used for the protoplast fusion, and 40% polyethylene glycol 4000 enabled the highest fusion frequency of about 20%. Some postfusion protoplasts showed cell divisions up to callus proliferation. Calli were screened by random amplified polymorphic DNA analysis for their hybrid character. Results revealed the existence of the hybrid calli. Some of the hybrid calli grew well with green color and shoot primordia. According to our knowledge, this is the first report about a hybrid formation between two haploid protoplasts. Potential comprehensive applications, as well as problems of this technique, are discussed.     

Haploid Plant Regeneration from Protoplast Cultures of Durum Wheat (Triticum durum Desf.)

Haploid suspension callus cultures from embryos of durum wheat (Triticum durum Desf. ) × maize (Zea mays L. ) crosses were used for protoplast isolation. Experimental results from enzyme digestion showed large numbers of viable protoplasts released from both suspension culture and solid culture of callus cut into small pieces of 1 mm in size prior to incubation in an enzyme solution containing 2.0% cellulase RS and 0.5 % pectolyase Y-23. Division frequency of protoplasts isolated from suspension cultured callus was quite different from that of solid cultured callus, however, the former being 5.20%, and the latter less than 1.0% when cultured on KM8p medium containing 1.0 mg/L 2, 4-D using LMP (low melting point) agarose embedding method. Embryogenic ealli could be selected out from protoplast-derived microcalli after 2 to 3 subcultures. Plants could be regenerated from protoplast-derived embryogenic calli after 20 days of culture on differentiation medium I (MS basal medium supplemented with 0.2 mg/L 2, 4-D, 1.0 mg/L BAP, 0. I mg/L NAA, 3 %/4 su- crose, 200 mg/L casein hydrolysate, 146 mg/L glutamine, 300 mg/L aspartic acid) and (components were the same as I without 2, 4-D) respectively. The plant regeneration frequency was about 20%. Chromosome count of root tip cells of 4 plants of the 22 protoplast- derived plants sampled at random revealed haploid in nature (2n= 2x= 14).     

An improved system to establish highly embryogenic haploid cell and protoplast cultures from pollen calluses of maize (Zea mays L.)

Regenerable, embryogenic haploid cell suspensions were initiated and established from type II pollen calluses of two selected Chinese maize genotypes (No 592 Y and 592.A2 LY). The induction frequency of friable, embryogenic callus (type II) was highly dependent on three factors: genotype, medium, cold pretreatment, and on their interactions. Repeated callus and cell selection during the culture procedure led to stable haploid suspensions consisting of fine clusters each containing 20–50 cells. The selected cell lines were able to maintain their morphogenic ability during long-term subculture (2 years). Protoplasts were successfully isolated from subcultured, friable, embryogenic pollen calluses and cultured on N₆BM and N₆K media using a feeder layer, obtained from 2-day-old suspension culture. Healthy plants were regenerated from protoplast-derived calluses.     

菘蓝花药培养及单倍体的诱导

探讨菘蓝花药处于单核晚期的形态指标,并以适宜发育时期的花药为外植体,进行花药培养及单倍体诱导。实验结果表明,4℃低温处理2d后,在含有6-BA0．5mg·L-1和NAA1．0mg·L-1。的Ms培养基上,花药愈伤组织的诱导率为23．35％;将其转接到Ms附加6．BA1．0mg·L-1,NAA0．5mg·L-1的分化培养基上,80．00％以上的愈伤组织可以诱导产生不定芽;再将分化出的试管苗转接到1／2MS＋NAA1．0mg·L-1的生根培养基上,3d左右即可获得完整植株。经叶边缘压片检查染色体数目,花药培养所得的弱小绿苗为单倍体植株。     

Regeneration of plants from Antirrhinum majus L. callus

Somaclone production in Antirrhinum majus plants by regeneration of plants from callus cultures has been achieved using three types of explant tissue. Regeneration from mature stem internode-derived callus was extremely poor. Callus derived from seedling shoot tips could be induced to form new shoots in six of seven cultivars tested. Regeneration was achieved in all seven cultivars when callus was produced from segments of hypocotyl and was most effective using agar-solidified medium containing 0.25 mgl^-1 naphthoxyacetic acid + 10% coconut milk. In this case, five of the cultivars produced shoots directly, one produced leaves from the petioles of which new shoots emerged, and one regenerated plants chiefly through the production of embryoids.     

An improved protocol for carrot haploid and doubled haploid plant production using induced parthenogenesis and ovule excision in vitro

In this work, we describe an improved protocol for induced parthenogenesis and ovule culture of carrot (Daucus carota L.). The effects of pollination with parsley pollen and/or 2,4-dichlorophenoxyacetic acid (2,4-D) treatment on the stimulation of parthenogenesis were studied using heterozygous donor plants of 30 varieties and breeding populations of carrots. Isolated ovules, cultured in vitro, enlarged and developed embryos or calli. The application of 2,4-D on pollinated flowers stimulated callus development but did not increase the frequency of embryo development from ovules and, thus, was not useful for increasing the frequency of haploid plant recovery. The efficiency of embryo development was accession-dependent and varied from 0 to 24.29%. In optimized conditions, most accessions responded by embryo development exclusively. The highest frequency of embryo development was observed from ovules excised from ovaries 20–22 d after pollination with parsley pollen. Among several media used for ovule culture, 1/2-strength Murashige and Skoog medium with 0.06 μM indole-3-acetic acid (IAA) was the best. It allowed the production of embryos at a similar frequency as on the media supplemented with kinetin, gibberellic acid, putrescine, or thidiazuron, but restricted callus development. Most plants obtained were haploids and diploids derived from parthenogenesis, as evidenced by homozygosity at three independent loci based on isozyme and PCR analyses. In total, considering haploids and embryo-derived homozygous diploids together, 72.6% of regenerated plants were of gametic origin.