Direct somatic embryogenesis from leaf and petiole explants of Spathiphyllum ‘Supreme’ and analysis of regenerants using flow cytometry

This study established a method of regenerating Spathiphyllum ??Supreme?? through direct somatic embryogenesis. Somatic embryos occurred in leaf and petiole explants cultured in the dark on a Murashige and Skoog basal medium supplemented with 2.27, 4.54, or 9.08???M N-phenyl-N??-1,2,3-thiadiazol-5-ylurea (TDZ) in combination with 1.08???M ??-naphthalene acetic acid or 2.26???M 2,4-dichlorophenoxyacetic acid (2,4-D). Explants with somatic embryos were transferred to fresh medium containing the same concentrations of growth regulators under lighted conditions for embryo conversion. The highest frequencies of leaf explants with somatic embryos and embryo conversion were both 84.4?%, which were induced by 9.08???M TDZ with 2.26???M 2,4-D. The frequencies for somatic embryo induction and embryo conversion were both 100?% when petiole explants were induced by 4.54???M TDZ with 2.26???M 2,4-D. The number of plantlets produced per leaf explant and petiole explant were as high as 67.4 and 74.4, respectively. Plantlets after transplanting to a soilless substrate grew vigorously in a shaded greenhouse. Liners were stable without phenotypic variation. Flow cytometry analysis of randomly selected plants showed that they all had a single identical peak. The mean nuclear DNA index for ??Supreme?? was 1.568, and the nuclear DNA content was 14.222?pg 2C^?1. The estimated genome size for ??Supreme?? was 6,954.5?Mbp 1C^?1 with a CV at 4.008?%. The results suggest that the regenerated plants have a stable ploidy level and this established regeneration method can be used for highly effective propagation of uniform Spathiphyllum ??Supreme??.     

Regeneration via somatic embryogenesis of the endangered wild arum (Arum palaestinum)

Somatic embryogenesis was obtained from callus of wild arum (Arum palaestinum). Callus was induced from sterilized corm bud sprouts cultured on basal medium containing 4.4???M 6-benzyladenine and 5.4???M 1-naphthaleneacetic acid. Callus was maintained under dark conditions using basal medium with 4.4 or 8.8???M 6-benzyladenine and 5.4 or 10.8???M 1-naphthaleneacetic acid. The highest callus weight and most desirable callus phenotype were achieved using basal medium containing 8.8???M 6-benzyladenine and 5.4???M 1-naphthaleneacetic acid. Friable calli were cultured in the dark on basal medium containing 4.5???M 2, 4-dichlorophenoxyacetic acid, 0.46???M 6-furfurylaminopurine, 5.4???M 1-naphthaleneacetic acid, and 1.7?mM proline to induce embryogenesis before transfer to regeneration medium. Embryos that developed on regeneration medium were transferred to medium minus plant growth regulators for germination. Ninety percent of the germinating embryos developed into rooted plantlets. Rooted plants were grown in the greenhouse and acclimatized successfully with a 95?% survival rate. This is the first report of successful somatic embryogenesis and plant regeneration in A. palaestinum.     

Plant regeneration through somatic embryogenesis from immature and mature zygotic embryos of Musa acuminata ssp. burmannica

A simple and efficient protocol has been developed for in vitro regeneration of M. acuminata ssp. burmannica (AA) plants. Somatic embryos were produced when immature and mature zygotic embryo explants were cultured on Murashige and Skoog medium supplemented with plant growth regulators 2,4-dichlorophenoxyacetic acid; (2,4-D), picloram or benzyl adenine and indole acetic acid. In general, immature embryos responded better than mature embryos. Callus proliferation was highest in medium supplemented with 2,4-D (4.5???M). Subsequent transfer of callus to fresh medium produced rapidly proliferating embryogenic calli. Embryogenic calli were maintained in complete darkness for 15?d followed by cycles of 8?h dark and 16?h light, under white fluorescent lamps with a light intensity of 3,000?lm/m² and at temperature of 28?±?2°C. Regeneration of embryogenic calli into plantlets was higher for immature embryos (76.6%) than for mature embryos (50.6%). This plant regeneration protocol using mature or immature zygotic embryos, via somatic embryogenesis, has significant potential to improve germination efficiencies of hybrid progenies used in conventional breeding strategies. Furthermore, tests on seed storage showed that seed viability rapidly decline after harvesting and was negligible after 9?mo of storage. This indicates using freshly harvested seeds as explant material is necessary for maximizing the tissue culture response.     

Improvement of somatic embryogenesis in wild cherry (Prunus avium). Effect of maltose and ABA supplements

Three different types of morphogenesis were identified in embryogenic cultures of Prunus avium grown on a proliferation medium containing 0.54 μM NAA, 0.46 μM kinetin and 0.44 μM BA: a friable hyperhydric callus, repetitive embryogenesis and an embryogenic tissue. Translucent and white somatic embryos were produced from the three types of morphogenesis but mainly from the embryogenic tissue. These somatic embryos showed histological and cytological teratological features such as highly differentiated cells with shrunken cytoplasm and destructured nuclei. For the four lines studied, somatic embryo production was improved by transferring the embryogenic tissue to developmental media without auxin and cytokinin but supplemented with maltose alone or maltose and 10 μM ABA. Three weeks after transfer, the line showing the most embryogenesis produced 1404 somatic embryos per gram of embryogenic tissue. A concentration of 263 mM maltose significantly increased the number of white somatic embryos for L 10 line, while translucent somatic embryo production was improved by 88 mM maltose for L 16 line. The combination of maltose and ABA produced different effects with each line. When used with 88 mM maltose, 10 μM ABA significantly increased white somatic embryo production for two lines but decreased the production for one line. When combined with 263 mM maltose, ABA had no effect on white somatic embryo production but significantly decreased the number of translucent somatic embryos. Cells of white somatic embryos contained protein storage reserves and numerous lipid bodies, while those of translucent embryos did not contain storage reserves or lipid bodies. After a two-month cold treatment conversion rate of white and translucent somatic embryos reached 8.5% and 35.2% respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Douglas fir embryogenic tissue initiation

Somatic embryogenesis (SE) is expected to play an important role in the future of US forests by providing increased productivity, sustainability, and uniformity. For broad scale implementation to occur, SE technology must work with a variety of genetically diverse trees. Douglas fir (Pseudotsuga menziesii (Mirb) Franco) is the dominant tree in the Pacific Northwest and has great economic and recreational value. We have developed a highly effective medium for initiation of embryogenic tissue of Douglas fir that contains ABA, biotin, brassinolide, folic acid, MES, pyruvic acid and can be used as a gelled medium or in a gelled-liquid medium overlay system. When tested with many high-value crosses over 2 years, initiation tests averaged initiation in the range of 40–57%. Additionally, a time- and labor-saving tetrazolium chloride embryo staining technique was developed to evaluate seed health and screen out seed sources likely to perform poorly in the initiation process.     

Plantlet Regeneration from Encapsulated and Non-encapsulated Desiccated Somatic Embryos of a Forest Tree: Sandalwood (Santalum album L.)

Somatic embryos obtained from embryogenic tissues of sandalwood (Santaium album) were grown on White’s medium containing abscisic acid, (ABA, 1.89, 3.78 or 18.92 μM) and various concentrations of sucrose (87.6 to 350.4 mM) to induce maturation. The embryos were isolated and desiccated for 10, 20 or 30 days: One lot of the desiccated somatic embryos was encapsulated in sodium alginate gel and the other lot was not encapsulated. Both encapsulated and nonencapsulated desiccated embryos showed revival of growth upon rehydration on White’s medium and developed into plants. The desiccation tolerance and regeneration of viable plantlets depended upon the pretreatment given to somatic embryos. Embryogenic tissue subjected to dry state for 30 days showed revival of somatic embryogenesis upon transfer to a fresh nutrient medium. Implications of maturation and desiccation of somatic embryos on its germinability are discussed.     

Somatic embryogenesis in loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis>) and Douglas fir (<Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis>): improving culture initiation and growth with MES pH buffer,biotin, and folic acid

Loblolly pine (Pinus taeda L.) somatic embryogenesis initiation was improved by supplementing the initiation medium with the pH buffer agent 2(n-morpholino)ethanesulphonic acid (MES) at 250 mg l^–1, folic acid at 0.5 mg l¹, and biotin at 0.05 mg l^–1. MES and vitamins increased the percentage of explants with extruded tissue that continued the initiation process to form embryogenic tissue. The increase in initiation was about 12%. Initiation of 12 open-pollinated families averaged 38.5%, which is 16% higher than initiation on medium without these additives. When tested with 18 control-pollinated families, initiation averaged 26.3%. Basal medium contained a combination of modified 1/2 P6 salts, activated carbon (AC) at 50 mg ^–1, Cu and Zn adjusted to compensate for adsorption by AC, 1.5% maltose, 2% myo-inositol, 500 mg l^–1 casamino acids, 450 mg l^–1 glutamine, 2 mg l^–1 NAA, 0.63 mg l^–1 BAP, 0.61 mg l^–1 kinetin, 3.4 mg l^–1 silver nitrate, 10 M 8-Br-cGMP, 0.1 M brassinolide, and 2 g l^–1 Gelrite. Early-stage embryo growth and initiation in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were also improved in the presence of these additives.     

Cyclic secondary somatic embryogenesis and efficient plant regeneration in mountain ash (Sorbus pohuashanensis)

An efficient protocol for secondary somatic embryogenesis in mountain ash is reported. Secondary somatic embryos (SSEs), initially obtained from primary embryos, were proliferated and maintained for more than 2?years via cyclic secondary somatic embryogenesis. SSEs were produced on the surfaces of cotyledons and radicles of maternal somatic embryos. Histological observations of the various stages of SSE development revealed four typical stages: globular, heart-shaped, torpedo, and cotyledon. Addition of a low concentration of naphthaleneacetic acid (NAA) to Murashige and Skoog (MS) medium resulted in the induction of SSEs, but addition of 2,4-dichlorophenoxyacetic acid (2,4-d) to MS medium decreased SSE formation. Addition of casein hydrolysate (CH) to MS medium promoted induction of SSEs. Cotyledonary SSEs were cultured on MS medium with 20?C60?g?L^?1 sucrose under light for 1?month until maturation. After transferred to MS medium containing either 0.06???M NAA or 0.15???M indole-3-butyric acid in the light, over 50?% of the mature SSEs developed into plantlets. Addition of 1.0?g?L^?1 activated charcoal was beneficial for SSE germination (over 60?%). At 18?°C, over 90?% of the germinated SSEs converted to plantlets on ? MS (half-strength of MS macroelements) with 1.8???M NAA under light. Plantlets acclimatized successfully to ex vitro conditions and field plants developed with normal phenotypes.     

Effect of growth regulators on maturation of geranium (Pelargonium × hortorum) somatic embryos

Interactions of growth regulators and polyethylene glycol on maturation of geranium somatic embryos were investigated. Somatic embryos were induced on medium with 20 M thidiazuron for 3 days. The growth regulators used were 1 µM abscisic acid, jasmonic acid, napthaleneacetic acid and benzylaminopurine at 21 days from the start of induction. Benzylaminopurine and napthaleneacetic acid did not enhance abscisic acid effects on maturation frequency but only improved maturation frequency in the presence of polyethylene glycol. Abscisic acid significantly improved protein content in the presence of polyethylene glycol. Benzylaminopurine and napthalene acetic acid in combination with abscisic acid and jasmonic acid improved protein types in somatic embryos only in the absence of polyethylene glycol. Osmoticum effected by polyethylene glycol seems the main component required for protein synthesis. This study showed significant improvement of somatic embryo quality for artificial seed production.     

Long-term somatic embryogenesis and maturation of somatic embryos in Hevea brasiliensis

A high frequency of secondary embryogenesis was induced from isolated early cotyledonary-stage somatic embryos of Hevea brasiliensis. A long-term embryogenic line was established by the use of recurrent embryogenesis and maintained for 3 years on hormone-free medium by the transfer of selected proembryogenic masses every 10 days.

The addition of 234 mM sucrose as stress with sucrose and 10⁻⁵ M abscisic acid (ABA) to the culture medium enhanced the maturation of somatic embryos. Under these culture conditions, the embryo population was composed of 45% globular, 18% oblong and 37% torpedo-stage embryos. These somatic embryos had well-formed tissue structure, a well-defined epidermis, protein storage bodies, and a high accumulation of starch. The triglyceride content was five times as high in the torpedo-stage embryos that developed on medium supplemented with 234 mM sucrose and 10⁻⁵ M ABA as in embryos obtained on basal medium with 58 mM sucrose.     

Abscisic acid and proline improve desiccation tolerance and increase fatty acid content of celery somatic embryos

Desiccation tolerance of celery (Apium graveolens L.) somatic embryos was increased by supplementation of embryo-production medium with 1 M abscisic acid (ABA) or 1 mM proline, with highest survival obtained with a combination of 1 M ABA and 1 mM proline. Addition of ABA and proline increased fatty acid accumulation by somatic embryos; the effect on fatty acid composition was inconsistent. Somatic embryos capable of germination differed from mature zygotic embryos by greater size, lower fatty acid level, and substantially lower proportion of oleic acid (18:1) as compared to linoleic acid (18:2).     

Enhancement of somatic embryogenesis and plant regeneration in Japanese larch (<Emphasis Type="Italic">Larix leptolepis</Emphasis>)

Different nitrogen sources, abscisic acid (ABA), gellan gum at various concentrations, and osmotica were evaluated for their effects on maturation of somatic embryo (SE) in Japanese larch (Larix leptolepis). Different concentrations of l-glutamine or casein hydrolysate (CH) in the medium were also compared. The highest number of matured embryos was obtained with ½ Litvay (LM) medium supplemented with 1.71 mM l-glutamine and 250 mg l^?1 CH. In terms of osmoticum effect, the highest number of cotyledonary SEs was produced in medium containing 0.2 M maltose. As for the effects of ABA and gellan gum concentration, the highest number of cotyledonary SEs was achieved on a medium containing 60 μM ABA and 0.8% gellan gum. In addition, the best plantlet conversion frequency (35.5%) was obtained with SEs derived from the treatment with 60 μM ABA and 0.8% gellan gum.     

Encapsulation technology for short-term storage and conservation of a woody climber, Decalepis hamiltonii Wight and Arn.

An efficient protocol was developed for short-term storage and conservation of a woody medicinal climber, Decalepis hamiltonii, using encapsulated nodal segments. The encapsulation of nodal segments was significantly affected by the concentrations of sodium alginate (Na-alginate) and calcium chloride (CaCl₂·2H₂O). A gelling matrix of 4?% Na-alginate and 100?mM CaCl₂·2H₂O was found most suitable for the production of ideal Ca-alginate beads. Maximum shoot re-growth (77.00?±?2.09?%) was recorded on Murashige and Skoog (MS) basal medium supplemented with 5.0???M 6-benzyladenine (BA), 0.5???M indole-3-acetic acid (IAA) and 30.0???M adenine-sulphate (ADS). Microshoots, recovered from encapsulated nodal segments (capsule) were best rooted on half-strength MS medium containing 2.5???M ??-naphthalene acetic acid (NAA). Complete plantlets (with shoot and root) were successfully acclimatized and established in field where they grew well without any detectable variation.     

Somatic embryogenesis in conifers—A case study of induction and development of somatic embryos in Picea abies

Vegetatively propagated material offers many advantages over seed material in forest tree breeding research and in reforestation programmes. Evidence is accumulating to suggest that using somatic embryos in forestry is a viable option. However, before somatic embryos can be used optimally in forestry, basic research aimed at increasing the number of responsive genotypes as well as the age of the primary explant is needed. This in turn requires the establishment of a basic understanding of the physiological and molecular processes that underlie the development of somatic embryos. The functions of genes and their developmental and tissue specific regulation are studied using transient and stable transformation techniques.The process of somatic embryogenesis can be divided into different steps: (1) initiation of somatic embryos from the primary explant, (2) proliferation of somatic embryos, (3) maturation of somatic embryos and (4) plant regeneration. Cortical cells in the primary explant are stimulated to go through repeated divisions so that dense nodules are formed from which somatic embryos differentiate. The first formed somatic embryos continue to proliferate and give rise to embryogenic cell lines. Embryogenic cell lines of Picea abies can be divided into two main groups A and B, based on morphology, growth pattern and secretion of proteins. Our results suggest that extracellular proteins play a crucial role in embryogenesis of Picea abies. Somatic embryos from group A can be stimulated to go through a maturation process when treated with abscisic acid. Mature somatic embryos can develop into plants.Abbreviations ABA abscisic acid - BA N⁶-benzyladenine - 2,4-D dichlorophenoxy acetic acid     

Significance of the zygotic seed coat on quiescence and desiccation tolerance of Medicago sativa L. somatic embryos

Summary The influence of the zygotic seed coat on precocious germination and desiccation tolerance of somatic embryos has been studied using alfalfa (Medicago sativa L.). When cultured in contact with somatic embryos, seed coats at certain developmental stages inhibited precocious germination and induced desiccation tolerance in the somatic embryos. Germination of somatic embryos was inhibited by seed coats at the age of 16–26 days after pollination (DAP) and desiccation tolerance was induced after 20–26 DAP. Both phenomena were related to the synthesis of abscisic acid in the seed coat. The absence of a quiescent phase and desiccation tolerance in alfalfa somatic embryos may be related to the lack of developmental control by the seed coat.Abbreviations ABA Abscisic acid - DAP Days after pollination     

Hormonal control of somatic embryo development from cultured cells of caraway: interactions of abscisic Acid, zeatin, and gibberellic Acid

The effects of abscisic acid, zeatin, and gibberellic acid on the development of somatic embryos from cultured cells of caraway (Carum carvi L.) were observed.     

Somatic embryogenesis from different tissues of Spanish populations of maritime pine

The somatic embryogenesis (SE) capacity of megagametophytes belonging to Continental and Mediterranean Spanish provenances of maritime pine (Pinus pinaster Aiton) was studied, noting factors (megagametophyte developmental stage and culture medium) that enhanced the induction and establishment of SE lines. In both provenances, initiation and establishment of embryogenic calli was higher on megagametophytes in which the dominant zygotic embryo had begun to develop. In the Mediterranean provenance, however, SE lines were also established from megagametophytes enclosing zygotic embryos with well-developed cotyledons. A modified Litvay medium (mLV) containing 9.9???M 2,4-dichlorophenoxyacetic acid (2,4-D) and 4.4???M 6-benzyladenine (BA) was superior to DCR medium containing 13.6???M 2,4-D and 4.4???M BA for SE induction, but there were no differences between media in terms of the number of SE lines established after 4?months in culture (153 vs. 155 established SE lines, for mLV and DCR media respectively). Of the 26 embryogenic lines tested for maturation, 15 (58?%) produced cotyledonary somatic embryos and 75?% of these gave rise to plants on germination medium. SE-like cultures from adult maritime pine trees were also initiated, but embryogenic lines could not be established. This is the first report on the production of SE in maritime pine of Continental and Mediterranean origin. The micropropagation protocols presented here provide an important tool for the vegetative multiplication of selected families and breeding programs for maritime pines from Spain.     

In vitro morphogenic response in cotyledon explants of Semecarpus anacardium L.

Three different morphogenic responses??caulogenesis, direct somatic embryogenesis, and callusing??were noted in cotyledon explants of Semecarpus anacardium L. cultured in woody plant medium (WPM) containing thidiazuron (TDZ). Thidiazuron, at all concentrations tested, induced organogenic as well as embryogenic responses. The organogenic buds differentiated to shoots and the embryogenic mass (EM) gave rise to globular embryos which differentiated up to cotyledon-stage embryos on repeated culture in growth regulator (GR)-free WPM medium containing 0.2% activated charcoal after the removal of TDZ. The organogenic and embryogenic responses were optimal in 9.08???M TDZ after the removal of TDZ. Elongated shoots rooted in half-strength liquid WPM medium with 2.46???M indole butyric acid. Plants were successfully acclimatized and transferred to soil. Histological studies confirmed the direct origin of the organogenic buds from the cotyledon explants. The EMs produced somatic embryos on repeated culture in charcoal incorporated GR-free medium. Morphogenic callus formation from the cotyledon explants was also noted. This callus on repeated culture in WPM medium with charcoal differentiated into somatic embryos. Repetitive somatic embryogenesis was evident from direct and indirectly formed primary embryos. The somatic embryos did not convert into plantlets, though sporadic germination of embryos was observed through the emergence of roots.     

Towards normalization of soybean somatic embryo maturation

Soybean (Glycine max L. Merrill) somatic embryos have been useful for assaying seed-specific traits prior to plant recovery. Such traits could be assessed more accurately if somatic embryos more closely mimicked seed development. Amino acid supplements, carbon source, and abscisic acid and basal salt formulations were tested in an effort to modify existing soybean embryogenesis histodifferentiation/maturation media to further normalize the development of soybean somatic embryos. The resultant liquid medium, referred to as soybean histodifferentiation and maturation medium (SHaM), consists of FNL basal salts, 3% sucrose, 3% sorbitol, filter-sterilized 30 mM glutamine and 1 mM methionine. SHaM-derived somatic embryos are more similar to seed in terms of protein and fatty acid/lipid composition, and conversion ability, than somatic embryos obtained from traditional soybean histodifferentiation and maturation media.     

Development and germination of Abies alba somatic embryos

Mature zygotic embryos of Abies alba mull were placed on a modified MCM medium (basal medium-BM) with 2.2 M benzyladenine and 2.3 M kinetin to induce embryogenic suspensor masses (ESM). These ESM proliferated on induction medium supplemented with 0.2 M 2,4-dichlorophenoxyacetic acid. From 61 ESM lines induced, 36 are still in culture after 2 years, of which 18 show embryogenic potential indicated by spontaneous formation of globular somatic embryos on the proliferation medium supplemented with 500–1000 mg l^-1 casein hydrolysate and 500 mg l^-1 l-glutamine. ESMs from cell line 2/56 were conditioned 1 week on BM with 58 mM sucrose and 10 g l^-1 activated charcoal for maturation of somatic embryos. Maturation was achieved on BM containing 20 M (±)cis-trans-abscisic acid in combination with 111 mM maltose. Organic nitrogen supplements improved the proliferation rate of cell line 2/56 as well as the maturation and vitality of the somatic embryos. Partial drying was necessary for subsequent root development. Plantlets with a root, primary needles and a terminal bud developed on BM when a combination of 30 mM sucrose and 50 mM maltose was provided as carbon source.Abbreviations BM basal medium - BA benzyladenine - ESM embryogenic suspensor mass - 2,4-d 2,4-dichlorophenoxyacetic acid - CH casein hydrolysate - l-gln l-glutamine - ABA (±) cis-trans-abscisic acid