DEVELOPMENTAL STUDIES IN PORPHYRA. I. BLADE DIFFERENTIATION IN PORPHYRA PERFORATA AS EXPRESSED BY MORPHOLOGY,ENZYMATIC DIGESTION,AND PROTOPLAST REGENERATION1

Four areas containing different cell morphologies were mapped on Porphyra blades and five different cell types (i.e. tapered with long extensions, large and vacuolated, vegetative and dividing, and reproductive: males and females) were identified in them. Tissues from these areas were dissociated, and protoplasts and single cells were isolated from the dissociated tissue of each distinct region. Regeneration rates of the isolated cells and protoplasts (isolates) varied depending on their morphological type. Regeneration rates were lowest in cultured isolates from the area just above the holdfast (ca. 1 %) and increased gradually to over 80% in isolates from areas of vegetative and reproductive regions away from the holdfast. Four distinct morphological patterns were observed among the regenerating plants. Cells isolated from vegetative areas developed into leafy plants while in liquid culture, and into calli when grown on solid medium. Isolates from reproductive areas developed into either a long thin or short thick filamentous plant. Those from ripe patches of carposporangia developed into thin conchocelis filaments, while isolates from non-differentiated cells bordering the ripe reproductive patches developed into thick filaments resembling the morphology of conchosporangial branches. The blade of Porphyra appears simple as it consists of a single cell layer; however, it is complex both morphologically and physiologically.     

Seaweed protoplasts: status,biotechnological perspectives and needs

Protoplasts are living plant cells without cell walls which offer a unique uniform single cell system that facilitates several aspects of modern biotechnology, including genetic transformation and metabolic engineering. Extraction of cell wall lytic enzymes from different phycophages and microbial sources has greatly improved protoplast isolation and their yield from a number of anatomically more complex species of brown and red seaweeds which earlier remained recalcitrant. Recently, recombinant cell wall lytic enzymes were also produced and evaluated with native ones for their potential abilities in producing viable protoplasts from Laminaria. Reliable procedures are now available to isolate and culture protoplasts from diverse groups of seaweeds. To date, there are 89 species belonging to 36 genera of green, red and brown seaweeds from which successful protoplast isolation and regeneration has been reported. Of the total species studied for protoplasts, most belonged to Rhodophyta with 41 species (13 genera) followed by Chlorophyta and Phaeophyta with 24 species each belonging to 5 and 18 genera, respectively. Regeneration of protoplast-to-plant system is available for a large number of species, with extensive literature relating to their culture methods and morphogenesis. In the context of plant genetic manipulation, somatic hybridization by protoplast fusion has been accomplished in a number of economically important species with various levels of success. Protoplasts have also been used for studying foreign gene expression in Porphyra and Ulva. Isolated protoplasts are also exploited in numerous miscellaneous studies involving membrane function, cell structure, bio-chemical synthesis of cell walls etc. This article briefly reviews the status of various developments in seaweed protoplasts research and their potentials in genetic improvement of seaweeds, along with needs that must to be fulfilled for effective realization of the objectives envisaged for protoplast research.     

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.     

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.     

Asymmetric somatic hybridization between wheat (Triticum aestivum) and Avena sativa L.

Protoplasts from cell suspensions of young-embryo-derived calli, which were nonregenerable for long-term subculture and protoplasts from embryogenic calli with the regeneration capacity of 75% of the same wheat Jinan 177, were mixed as recipient. Protoplasts from embryogenic calli of Avena sativa (with the regeneration capacity of less than 10%) irradiated with UV at an intensity of 300 μW/cm² for 30 s, 1 min, 2 min, 3 min, 5 min were used as the donor. Protoplasts of the recipient and the donor were fused by PEG method. Many calli and normal green plants were regenerated at high frequency, and were verified as somatic hybrids by chromosome counting, isozyme, 5S rDNA spacer sequence analysis and GISH (genomic in situ hybridization). Fusion combination between protoplasts either from the cell suspensions or from the calli and UV-treated Avena sativa protoplasts could not regenerate green plants.     

Effect of protoplast source and media on growth and regenerability of protoplast-derived calluses of Solanum tuberosum L

Freshly isolated mesophyll and suspensions-cell protoplasts of S. tuberosum cvs. Desiree and Maris Piper were cultured in different media i.e. modified MS, V-KM and MS-KM. Protoplast plating efficiencies were higher in MS-KM medium. Resulting protoplast-derived calluses were transferred either onto the medium of Bokelmann and Roest (1983) or that of Lam (1977) for shoot regeneration. Calluses derived from mesophyll cell protoplasts differentiated about 2 weeks earlier than calluses derived from suspension-cell protoplasts. Shoot initiation was also about 2 weeks earlier from calluses subcultured onto the former medium as compared to the latter.     

Efficient plant regeneration from protoplasts isolated from embryogenic suspension cultures of Cyclamen persicum Mill.

A protocol for plant regeneration from protoplasts has been developed, and then successfully applied to different genotypes of Cyclamen persicum Mill. Protoplasts were isolated from embryogenic suspension cultures by enzymatic digestion in 2% cellulase R10 and 0.5% macerozyme R10. Yields obtained varied between 1 and 5 × 10⁵ protoplasts per gram fresh mass depending on the genotype. Protoplasts were immobilized in alginate films, which promoted proper cell wall regeneration. The highest cell division frequencies were found in modified Kao and Michayluk (1975, Planta 126:105–110) medium containing the same types and concentrations of plant growth regulators that were applied for suspension culture (2.0 mg l⁻¹ 2,4-dichlorophenoxyacetic acid and 0.8 mg l⁻¹ 6-(γ,γ-dimethylallylamino)purine). Cell division was recorded for all 11 tested genotypes in frequencies of up to 12% and 18% after 7 and 14 days, respectively. However, cell division frequency varied strongly between different genotypes. After 4–6 weeks calluses were released from the alginate films and further cultured on hormone-containing medium for continued growth or transferred to hormone-free medium for regeneration of somatic embryos. Plant regeneration via somatic embryogenesis succeeded in 9 out of the 11 genotypes under investigation. Up to now protoplast-derived plants from four genotypes have been successfully transferred to soil.     

Plant regeneration from mesophyll protoplasts of Centaurea cyanus,Senecio x hybridus and Callistephus chinensis

Protoplasts were isolated from leaves of glasshouse-grown plants of Centaurea cyanus and axenic shoot cultures of Senecio x hybridus. Upon culture, using modified MS-based media, protoplasts of both systems entered division to produce callus, followed by plant regeneration. Leaf protoplasts of Callistephus chinensis entered sustained division only following the preconditioning for 24h of peeled leaf tissues on agar-solidified MS-based medium. Protoplasts were also isolated from cell suspensions of C. chinensis and divided in MS-based or KM media. However, only leaf mesophyll protoplasts of Callistephus produced callus, which developed shoots.The establishment of protoplast-to-plant protocols for these ornamental species has provided a basis for broadening their gene pools through somatic hybridisation.Abbreviations BAP 6-benzylaminopurine - NAA -naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog (1962) - KM Kao and Michayluk (1975) - g.f.wt. gram fresh weight     

Regeneration of isolated mesophyll and cell suspension protoplasts to plants in Stylosanthes guianensis. A tropical forage legume

Protoplasts were isolated from leaf mesophyll and cell suspensions of two accessions of Stylosanthes guianensis (Aubl.), a tropical forage legume. When cultured in VKM liquid culture medium, both types of protoplasts divided at a rate of 4–8%, and subsequently formed cell colonies. Protoplast-derived calluses produced numerous shoots when transferred to regeneration medium. Regenerated shoots could be easily rooted, and plantlets were transferred to soil. The effects of several factors on the efficiency of this protoplast system have been investigated.Abbreviations BAP 6-benzylaminopurine - GA₃ Gibberellic acid - NAA Naphthalene acetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - Zea Zeatin     

Inherited chilling tolerance in somatic hybrids of transgenic Hibiscus rosa-sinensis x transgenic Lavatera thuringiaca selected by double-antibiotic resistance

Summary Improvement of Hibiscus rosa-sinensis for increased frost tolerance has been attempted through somatic hybridization with the frost tolerant Lavatera thuringiaca. Cell suspensions from Hibiscus and Lavatera were transformed with A. tumefaciens harboring plasmids containing selectable genes coding for kanamycin and hygromycin resistance, respectively. We provided evidence that H. rosa-sinensis and L. thuringiaca were transformed by strong selection of transformed calluses in medium containing antibiotics, by GUS activity determination in protein extracts and by molecular confirmation of chromosomal integration and expression of the selectable genes. Protoplasts isolated from a kanamycinresistant Hibiscus callus and from a hygromycin-resistant Lavatera callus were fused and selected in medium containing both antibiotics. We determined unambiguously that the regenerated double-antibiotic resistant clones obtained are indeed somatic hybrids through analysis of acid phosphatase zymograms and nuclear DNA content. Plant regeneration through somatic embryogenesis was accomplished from both isolated protoplasts and transgenic calluses of L. thuringiaca. However, regeneration from the double-antibiotic resistant fusant calluses was unsuccessful. Analysis of the somatic hybrids at the callus level showed that chilling and freezing tolerance are governed by independent genetic components. The somatic hybrids displayed significant improvement for chilling tolerance at conditions lethal to H. rosa-sinensis, although frost tolerance was not expressed.     

Responses of cells and protoplasts of Coffea arabica genotypes to partially purified culture filtrates produced by Colletotrichum kahawae

Hypocotyl-derived calli of genotypes and segregating populations of Coffea arabica, differing in susceptibility to Colletotrichum kahawae, were used to produce cell suspensions and protoplasts which were exposed to partially purified culture filtrates (PPCFs) prepared from the pathogen. The growth and viability of PPCF-treated cells and protoplasts were measured using packed cell volume, fluorescein diacetate staining and a colorimetric assay involving the tetrazolium salt MTT. Differential responses of cells and protoplasts were influenced by genotype, time of exposure and PPCF concentration. Protoplasts of resistant genotypes responded differentially from more susceptible genotypes as early as 4 h after challenge with the phytotoxin, suggesting that they were more sensitive than cell suspensions to the treatments. Protoplasts exposed to PPCFs from C. kahawae may therefore be used to screen and select genotypes resistant to, or tolerant of, coffee berry disease. Received: 10 April 1996 / Revision received: 25 August 1996 / Accepted: 15 September 1996     

Rhizogenesis fromNigella sativa protoplasts

Summary Protoplasts were isolated for the first time from cell suspensions ofNigella sativa. These were then cultured in media and observed at regular intervals. Different concentrations of auxin and kinetin were tried with success to obtain root from the callus tissues of the protoplasts.     

Callus production from willow (Salix viminalis L.) protoplasts

Protoplasts were isolated from cell suspensions of Salix viminalis (basket willow) clone 78-0-90 and S. schwerinii clone 77-0-77, using cellulysin and macerase in modified Woody Plant medium. For clone 78-0-90, 6.3 · 10⁶ ± 1.9 · 10⁶ protoplasts were obtained per gram fresh weight. Cell divisions started two days after protoplast isolation and gave rise to callus which has been maintained in culture for up to four years. Protoplast yield from the clone 77-0-77 was lower (less than 10⁶ protoplasts per gram cells), cell division was infrequent and no callus was obtained. Protoplasts were also isolated from the leaves of willow shoot cultures using cellulysin and pectolyase, but these did not show cell divisions.Abbreviations BA benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - MS medium Murashige & Skoog (1962) medium - WP medium Woody Plant medium (Lloyd & McCown 1981)     

A simple,versatile feeder layer system for Brassica oleracea protoplast culture

Protoplasts from cauliflower (Brassica oleracea ssp. botrytis) and broccoli (ssp. italica) leaves and hypocotyls were successfully cultured on membrane filters over a feeder layer of cells from a B. campestris suspension culture. Cells from rice, tomato and tobacco suspensions were not as effective as the B. campestris cells. Plants were recovered from protoplasts of previously recalcitrant Brassica genotypes. Protoplasts cultured in low numbers (10–100) on the feeder layer divided and formed colonies capable of plant regeneration, as did fused protoplasts.Abbreviations BA 6-benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - NAA naphthaleneacetic acid - PCV packed cell volume     

Morphological and ultrastructural studies on protoplast production and reversion of the higher basidiomyceteAgaricus bisporus

Protoplasts have been isolated from young vegetative mycelia ofAgaricus bisporus by an enzyme mixture of novozym and chitinase. Protoplasts were released through ruptures in the wall, initially at the apices, but also later from older parts of the hyphae, indicating that they may lack the cell wall. The process of regeneration of these protoplasts has been investigated in liquid medium in which the protoplasts produced short chains of convoluted cells that finally produced a hypha. Electron microscopy has shown that at the start of regeneration two different kinds of fibrils were produced at the external surface of the protoplasts. Later, the thickness of the cell wall increased, and there was a deposit of amorphous material giving rise to a complete new wall.     

Plant regeneration from protoplasts of wild barley (Hordeum murinum L.)

Summary We have produced a large number of plants regenerated from protoplasts originally isolated from embryo-derived cell suspensions of wild barley, Hordeum murinum L.. Suspensions initially allowed protoplast isolation and culture 5.5 to 9 months from the date of callus initiation. Colony formation efficiencies ranged from 1.5 to 3.0 % and from 0.1 to 1.4 % for protoplast cultures with and without nurse cells, respectively. Both nurse and non-nurse techniques allowed efficient embryogenesis and plant regeneration. More than 400 shoots/plantlets have been obtained from 6 independent experiments. Over 150 plants have been transferred to the greenhouse. Protoplasts isolated from the youngest suspensions (5.5 months old) gave rise to the largest number of plants. Protoplasts isolated from suspensions as old as 15 months were also regenerable.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP 6-benzylaminopurine - NAA naphthaleneacetic acid - L1, L2 medium according to Lazzeri et al. 1991 - L3 medium medium according to Jähne et al. 1991a     

Plant regeneration of rose (Rosa hybridia) from embryogenic cell-derived protoplasts

Culture conditions are described for sustained cell division and plant regeneration from protoplasts of rose (Rosa hybrida L. `Sumpath'). Protoplasts were enzymatically isolated from 2-week-old embryogenic cell suspension cultures. Freshly isolated protoplasts were plated as a thin layer onto protoplast culture medium (half-strength 21 Murashige and Skoog's medium containing 60 g l^–1 myo-inositol, 4.4 M BA, and 1.4 M 2,4-D) at a density of 5×10⁴ protoplasts ml^–1. The plating efficiency reached 3.9% after 2 weeks of culture. However, few protoplasts underwent cell division when cultured in protoplast culture medium in which 60 g l^–1 myo-inositol was replaced with the same osmolarity of 90 g l^–1 mannitol, indicating that myo-inositol is essential for sustained cell division of protoplasts. Colonies were formed after 8 weeks of culture at a frequency of 0.2%. Colonies were then transferred to colony culture medium (0.4% Gelrite-solidified protoplast culture medium) and maintained by subculturing at 4-week intervals to form embryogenic calluses. Upon transfer to half-strength MS basal medium, embryogenic calluses gave rise to numerous somatic embryos. Somatic embryos were transferred to half-strength MS basal medium containing 48 mg l^–1 ferric ethylenediamine di-(o-hydroxyphenylacetate), where they subsequently developed into plantlets at a frequency of 30.9%. The plantlets had the same chromosome number of 2n=3x=21 as the source plant. They were successfully transplanted to potting soil and grown to maturity in a greenhouse.     

Plant regeneration from mesophyll protoplasts of Matthiola incana (L.) R. Br.

Summary A protocol for obtaining regenerated fertile plants from mesophyll protoplasts of three lines of Matthiola incana is described. Protoplasts were isolated from leaves of 21–28 days old Matthiola plants grown in controlled environment. Sustained divisions were achieved when protoplasts were embedded in sodium alginate. Up to 2.0 % of the protoplasts developed into colonies which could be transferred to shoot regeneration media. More than 25 % of the obtained calluses regenerated shoots. About 4 % of these shoots could be rooted and after transfer to soil phenotypically normal plants have been obtained.Abbreviations 2,4-D 2,4-dichlorphenoxyacetic acid - NAA naphthalene acetic acid - IAA indole-3-acetic acid - BAP 6-banzylaminopurine - IPA isopentenyladenine - IPAR isopentenyladenosine - MES (2-[N-morpholino]) ethanesulfonic acid     

Protoplasts formation inFusarium species

Formation of protoplasts from four species ofFusarium genus is described. Protoplasts were isolated from mycelium by enzymatic digestion of the cell wall in the presence of an osmotic stabilizer. The results obtained differed between the studied species. Best yields of protoplasts were obtained fromF. moniliforme (90 % cells as protoplasts).     

Chloroplast number in guard cells as ploidy indicator of in vitro-grown androgenic pepper plantlets

Protoplasts were isolated from field and in vitro-grown leaves, cotyledons and cell suspension cultures (of ovule callus origin) of the scion apple cultivars Starkrimson, Rainier, Qiujin and Liaofu. Fast-growing calluses were obtained from leaf, cotyledon and cell suspension derived protoplasts of the four genotypes. The best proliferation responses were obtained from cell suspension protoplasts. For all genotypes tested, nodular calluses were obtained from protoplasts that had originally been cultured on K8P medium, but only those of cultivar Starkrimson underwent organogenesis. In this cultivar shoot buds were produced on callus derived from both cotyledon and cell suspension protoplasts and complete plants. This is the first example of whole plant regeneration from protoplasts isolated from an undifferentiated tissue in apple.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - IAA 3-indole acetic acid - IBA 3-indole butyric acid - LH lactalbumin hydrolysate - MS Murashige & Skoog (1962) - NAA 1-naphthaleneacetic acid - TDZ thidiazuron - VC L(+) ascorbic acid