In-ovulo embryo culture and seedling development of cotton (Gossypium hirsutum L.)

Identification, characterization and expression profiling of circular RNAs in the early cotton fiber developmental stages

Circular RNA is one of the endogenous non-coding RNAs with a covalently closed loop structure and largely involved in regulating gene expression. However, the abundance of circular RNAs and their regulatory functions during the early stages of fiber development are still not known. In this work, we conducted high-throughput sequencing of the Ligonlintless-1 and its wild-type at 0 DPA, 8 DPA and stem. A total of 2811 circular RNAs were identified and unevenly distributed across cotton chromosomes. We found 34, 142 and 27 circular RNAs were differentially expressed between Ligonlintless-1 and wild-type at 0 DPA, 8 DPA and stem, respectively. Both circular RNA-microRNA-mRNA network and MeJA treatment results in Ligonlintless-1 and wild-type might provide a strong indication of four circular RNAs and ghr_miR169b being important biological molecular associating with fiber development. The results provide new insight into the putative molecular function of circular RNAs in the regulation of fiber development.

Embryogenic Calli Explants and Silicon Carbide Whisker-Mediated Transformation of Cotton (Gossypium hirsutum L.)

Rapid growth in the genetic transformation of plants is the outcome of versatile transformation methods, explant nature, and media regimes. Modern biotechnologists have now a toolkit embraced with different plant transformation methods to generate specific and targeted genetic variation for performance improvement of crop plants. Genetic information are created by proper custom synthesis/amplification of DNA sequences from natural sources, modification during gene cloning, and choice of regulatory sequences and delivered to plants via different plant transformation techniques. Cotton is known by different names like king of fiber crops, white gold, etc., due to its socioeconomic involvement in society livelihood. So cotton is the host of several transgenes delivered for the purpose of trait development of improvement outcompeting its wild counterparts. At present most of the cotton adopted by farmers is biotech and contributes significantly in meeting farmers and industry demands. It is the versatile nature of cotton that it has been subjected to different genetic transformation methods to provide the breeders with an opportunity to develop alien traits or improve the endogenous gene performance that are very difficult or impossible to develop through conventional breeding methods. Landmark achievements were achieved by expanding explant choice such as calli as explants as it reduces the extent of labor, time, and effort and thereby becoming cost-effective cotton transformation. Cotton calli becomes differentiated into embryogenic and non-embryogenic which requires regular screening, keeping in view texture, color, and growth behavior. Here we describe the calli features which are peculiar in nature when used as explants in a novel physical way of cotton transformation with different genes by using embryogenic calli as continuous source of explants. The dawn of genome editing has opened another horizon in transformation research and development enhancing the scope of cotton transformation.

Alternative oxidase (AOX) over-expression improves cell expansion and elongation in cotton seedling exposed to cool temperatures

KEY MESSAGE

Evidence that supports a relation between AOX expression and improvement in plant height, internode length, and total leaf area under cool temperature is shown. Cell expansion and elongation appear to be enhanced when AOX expression was increased. Cotton growth is sensitive to cool temperature during germination and early seedling development. Delayed emergence, seedling damage, and increased risk to disease are common. Late seasonal cool weather is a major factor limiting the consistent production of high-quality cotton lint in West Texas. Alternative oxidase functions in the inner membrane of the mitochondria via an alternative respiration pathway and serves as a multifunctional system for amelioration of abiotic and biotic stresses. Cotton seedling emergence and growth exposed to cool temperatures was examined in plants with enhanced AOX expression. Thirteen T1 seed lines showed 3 to 1 segregation for the T-DNA containing the tobacco AOX1 gene. Two over-expressing, single-copy, homozygous AOX lines (94-20T and 66-6T) and Null line (94-3N) were selected for examination. The transcript levels were ≈ 2 to 6 fold higher in the AOX lines compared to those of the Null line and wild-type in stem, leaf, root and boll tissues. The research examined the hypothesis that transgenic cotton with enhanced AOX expression will have enhanced growth traits under suboptimal cool temperatures. Improved plant height, internode length, plant height and internode length from second node, and total leaf area under cool temperatures were observed in AOX over-expression lines. This may be attributed to improved cell expansion and elongation characteristics in the AOX line.

Gossypium arboreum Accessions Resistant to Rotylenchulus reniformis

In the southeastern United States, reniform nematode (Rotylenchulus reniformis) is a serious pest of upland cotton (Gossypium hirsutum), a species which has no naturally occurring resistance against this nematode. To identify sources of reniform nematode resistance in species closely related to upland cotton, 222 G. arboreum accessions from the U.S. germplasm collection were evaluated in repeated growth chamber experiments. In initial screenings, root infection was measured 4 wks after inoculation. The 15 accessions supporting the fewest infections (PI 529992, PI 615755, PI 615766, PI 615788, PI 615848, PI 615856, PI 615950, PI 615977, PI 615991, PI 616008, PI 616016, PI 616062, PI 616126, PI 616159, and A2 553) were evaluated again in confirmation tests lasting 8 wk. The combined totals of nematodes extracted from soil and eggs extracted from roots were analyzed. All 15 accessions tested supported significantly smaller reniform nematode populations than the susceptible controls (G. hirsutum cultivar Deltapine 16 and G. arboreum accession PI 529729). Nine accessions (PI 529992, PI 615755, PI 615766, PI 615788, PI 615856, PI 615950, PI 615991, PI 616008, and PI 616159) supported reniform nematode populations comparable to the resistant control (G. arboreum accession PI 615699), and accession PI 615848 had significantly fewer reniform nematodes than the resistant control. Cotton breeders would benefit from introgressing the newly identified resistance from these accessions into their upland cotton improvement programs.

A New Synthetic Amphiploid (AADDAA) between Gossypium hirsutum and G. arboreum Lays the Foundation for Transferring Resistances to Verticillium and Drought

Gossypium arboreum, a cultivated cotton species (2n = 26, AA) native to Asia, possesses invaluable characteristics unavailable in the tetraploid cultivated cotton gene pool, such as resistance to pests and diseases and tolerance to abiotic stresses. However, it is quite difficult to transfer favorable traits into Upland cotton through conventional methods due to the cross-incompatibility of G. hirsutum (2n = 52, AADD) and G. arboreum. Here, we improved an embryo rescue technique to overcome the cross-incompatibility between these two parents for transferring favorable genes from G. arboreum into G. hirsutum. Our results indicate that MSB2K supplemented with 0.5 mgl^-1 kinetin and 250 mg^-1 casein hydrolysate is an efficient initial medium for rescuing early (3 d after pollination) hybrid embryos. Eight putative hybrids were successfully obtained, which were further verified and characterized by cytology, molecular markers and morphological analysis. The putative hybrids were subsequently treated with different concentrations of colchicine solution to double their chromosomes. The results demonstrate that four putative hybrid plants were successfully chromosome-doubled by treatment with 0.1% colchicine for 24 h and become amphiploid, which were confirmed by cytological observation, self-fertilization and backcrossing. Preliminary assessments of resistance at seedling stage indicate that the synthetic amphiploid showed highly resistant to Verticillium and drought. The synthetic amphiploid between G. hirsutum × G. arboreum would lay the foundation for developing G. arboreum-introgressed lines with the uniform genetic background of G. hirsutum acc TM-1, which would greatly enhance and simplify the mining, isolation, characterization, cloning and use of G. arboreum-specific desirable genes in future cotton breeding programs.

Overexpression of rice NAC gene SNAC1 improves drought and salt tolerance by enhancing root development and reducing transpiration rate in transgenic cotton

The SNAC1 gene belongs to the stress-related NAC superfamily of transcription factors. It was identified from rice and overexpressed in cotton cultivar YZ1 by Agrobacterium tumefaciens-mediated transformation. SNAC1-overexpressing cotton plants showed more vigorous growth, especially in terms of root development, than the wild-type plants in the presence of 250 mM NaCl under hydroponic growth conditions. The content of proline was enhanced but the MDA content was decreased in the transgenic cotton seedlings under drought and salt treatments compared to the wild-type. Furthermore, SNAC1-overexpressing cotton plants also displayed significantly improved tolerance to both drought and salt stresses in the greenhouse. The performances of the SNAC1-overexpressing lines under drought and salt stress were significantly better than those of the wild-type in terms of the boll number. During the drought and salt treatments, the transpiration rate of transgenic plants significantly decreased in comparison to the wild-type, but the photosynthesis rate maintained the same at the flowering stage in the transgenic plants. These results suggested that overexpression of SNAC1 improve more tolerance to drought and salt in cotton through enhanced root development and reduced transpiration rates.

Phytochrome RNAi enhances major fibre quality and agronomic traits of the cotton Gossypium hirsutum L

Simultaneous improvement of fibre quality, early-flowering, early-maturity and productivity in Upland cotton (G. hirsutum) is a challenging task for conventional breeding. The influence of red/far-red light ratio on the fibre length prompted us to examine the phenotypic effects of RNA interference (RNAi) of the cotton PHYA1 gene. Here we show a suppression of up to ~70% for the PHYA1 transcript, and compensatory overexpression of up to ~20-fold in the remaining phytochromes in somatically regenerated PHYA1 RNAi cotton plants. Two independent transformants of three generations exhibited vigorous root and vegetative growth, early-flowering, significantly improved upper half mean fibre length and an improvement in other major fibre characteristics. Small decreases in lint traits were observed but seed cotton yield was increased an average 10-17% compared with controls. RNAi-associated phenotypes were heritable and transferable via sexual hybridization. These results should aid in the development of early-maturing and productive Upland cultivars with superior fibre quality.

Targeted molecular trait stacking in cotton through targeted double-strand break induction

Recent developments of tools for targeted genome modification have led to new concepts in how multiple traits can be combined. Targeted genome modification is based on the use of nucleases with tailor-made specificities to introduce a DNA double-strand break (DSB) at specific target loci. A re-engineered meganuclease was designed for specific cleavage of an endogenous target sequence adjacent to a transgenic insect control locus in cotton. The combination of targeted DNA cleavage and homologous recombination-mediated repair made precise targeted insertion of additional trait genes (hppd, epsps) feasible in cotton. Targeted insertion events were recovered at a frequency of about 2% of the independently transformed embryogenic callus lines. We further demonstrated that all trait genes were inherited as a single genetic unit, which will simplify future multiple-trait introgression.

Silicon carbide whisker-mediated transformation of cotton (Gossypium hirsutum L.)

Plant transformation methods are invaluable biotechnological tools to generate specific and targeted genetic variation for performance improvement of crop plants. Genetic information is created by proper modification during gene cloning flanked by proper regulatory sequences and delivered to plants via -different plant transformation techniques. Due to being a multipurpose plant, cotton has been subjected to different genetic transformation methods to provide the breeders with an opportunity to develop alien traits or improve the endogenous gene performance that are very difficult or impossible to develop through conventional breeding methods. Here we describe the novel physical way of cotton transformation with different genes by using embryogeneic calli as continuous source of explants.

Expression of an Arabidopsis vacuolar H+-pyrophosphatase gene (AVP1) in cotton improves drought- and salt tolerance and increases fibre yield in the field conditions

The Arabidopsis gene AVP1 encodes a vacuolar pyrophosphatase that functions as a proton pump on the vacuolar membrane. Overexpression of AVP1 in Arabidopsis, tomato and rice enhances plant performance under salt and drought stress conditions, because up-regulation of the type I H+-PPase from Arabidopsis may result in a higher proton electrochemical gradient, which facilitates enhanced sequestering of ions and sugars into the vacuole, reducing water potential and resulting in increased drought- and salt tolerance when compared to wild-type plants. Furthermore, overexpression of AVP1 stimulates auxin transport in the root system and leads to larger root systems, which helps transgenic plants absorb water more efficiently under drought conditions. Using the same approach, AVP1-expressing cotton plants were created and tested for their performance under high-salt and reduced irrigation conditions. The AVP1-expressing cotton plants showed more vigorous growth than wild-type plants in the presence of 200 mM NaCl under hydroponic growth conditions. The soil-grown AVP1-expressing cotton plants also displayed significantly improved tolerance to both drought and salt stresses in greenhouse conditions. Furthermore, the fibre yield of AVP1-expressing cotton plants is at least 20% higher than that of wild-type plants under dry-land conditions in the field. This research indicates that AVP1 has the potential to be used for improving crop's drought- and salt tolerance in areas where water and salinity are limiting factors for agricultural productivity.

Expression of an Arabidopsis vacuolar sodium/proton antiporter gene in cotton improves photosynthetic performance under salt conditions and increases fiber yield in the field

Drought and salinity are two major limiting factors in crop productivity. One way to reduce crop loss caused by drought and salinity is to increase the solute concentration in the vacuoles of plant cells. The accumulation of sodium ions inside the vacuoles provides a 2-fold advantage: (i) reducing the toxic levels of sodium in cytosol; and (ii) increasing the vacuolar osmotic potential with the concomitant generation of a more negative water potential that favors water uptake by the cell and better tissue water retention under high soil salinity. The success of this approach was demonstrated in several plants, where the overexpression of the Arabidopsis gene AtNHX1 that encodes a vacuolar sodium/proton antiporter resulted in higher plant salt tolerance. Overexpression of AtNHX1 increases sodium uptake in vacuoles, which leads to increased vacuolar solute concentration and therefore higher salt tolerance in transgenic plants. In an effort to engineer cotton for higher drought and salt tolerance, we created transgenic cotton plants expressing AtNHX1. These AtNHX1-expressing cotton plants generated more biomass and produced more fibers when grown in the presence of 200 mM NaCl in greenhouse conditions. The increased fiber yield was probably due to better photosynthetic performance and higher nitrogen assimilation rates observed in the AtNHX1-expressing cotton plants as compared with wild-type cotton plants under saline conditions. Furthermore, the field-grown AtNHX1-expressing cotton plants produced more fibers with better quality, indicating that AtNHX1 can indeed be used for improving salt stress tolerance in cotton.

High-stearic and High-oleic cottonseed oils produced by hairpin RNA-mediated post-transcriptional gene silencing

We have genetically modified the fatty acid composition of cottonseed oil using the recently developed technique of hairpin RNA-mediated gene silencing to down-regulate the seed expression of two key fatty acid desaturase genes, ghSAD-1-encoding stearoyl-acyl-carrier protein Delta 9-desaturase and ghFAD2-1-encoding oleoyl-phosphatidylcholine omega 6-desaturase. Hairpin RNA-encoding gene constructs (HP) targeted against either ghSAD-1 or ghFAD2-1 were transformed into cotton (Gossypium hirsutum cv Coker 315). The resulting down-regulation of the ghSAD-1 gene substantially increased stearic acid from the normal levels of 2% to 3% up to as high as 40%, and silencing of the ghFAD2-1 gene resulted in greatly elevated oleic acid content, up to 77% compared with about 15% in seeds of untransformed plants. In addition, palmitic acid was significantly lowered in both high-stearic and high-oleic lines. Similar fatty acid composition phenotypes were also achieved by transformation with conventional antisense constructs targeted against the same genes, but at much lower frequencies than were achieved with the HP constructs. By intercrossing the high-stearic and high-oleic genotypes, it was possible to simultaneously down-regulate both ghSAD-1 and ghFAD2-1 to the same degree as observed in the individually silenced parental lines, demonstrating for the first time, to our knowledge, that duplex RNA-induced posttranslational gene silencing in independent genes can be stacked without any diminution in the degree of silencing. The silencing of ghSAD-1 and/or ghFAD2-1 to various degrees enables the development of cottonseed oils having novel combinations of palmitic, stearic, oleic, and linoleic contents that can be used in margarines and deep frying without hydrogenation and also potentially in high-value confectionery applications.

In vitro induction of multiple shoots and plant regeneration in cotton (Gossypium hirsutum L.)

Induction of multiple shoots in cotton (Gossypium hirsutum L. cv. Anjali-LRK 516) has been achieved with cotyledonary nodes devoid of cotyledons and apical meristems. Explants from 35-day-old seedlings yielded the maximum number of shoots (4.7 shoots/explant) using Murashige and Skoog (MS) basal medium supplemented with 6-benzylaminopurine and kinetin (2.5 mg/1 each). Explants from 35-day-old seedlings raised in glass bottles produced a higher number of multiple shoots (8.3 shoots/explant) than those grown in glass tubes and cultured on the same shoot induction medium. Elongation of multiple shoots was obtained on liquid or agar MS basal medium without phytohormones. In vitro shoots were rooted on half-strength agar-solidified MS basal medium or with 0.05 or 0.1 mg/1 naphthaleneacetic acid. Hardening and survival of tissue culture plantlets was 95% under greenhouse conditions.

Engineering 2,4-D resistance into cotton

To reduce damage by drift-levels of the herbicide 2,4-dichlorophenoxyacetic acid, we have engineered the 2,4-D resistance trait into cotton (Gossypium hirsutum L.). The 2,4-D monooxygenase gene tfdA from Alcaligenes eutrophus plasmid pJP5 was isolated, modified and expressed in transgenic tobacco and cotton plants. Analyses of the transgenic progeny showed stable transmission of the chimeric tfdA gene and production of active 2,4-D monooxygenase. Cotton plants obtained were tolerant to 3 times the field level of 2,4-D used for wheat, corn, sorghum and pasture crops.

In vitro selection and regeneration of cotton resistant to high temperature stress

Cell suspension cultures of cotton (Gossypium hitirsutum L. cv. Coker 312) were exposed to various temperature:time treatments in order to select cell lines resistant to high temperature stress. Cells were exposed to 45°C for 3 h each day until the total accumulated hours of stress were: 0 h, 10 h, 75 h, 100 h, or 105 h (81 h pulsed then 24 h continuous). After the stress treatments, the cells were plated onto embryo development medium and plants were recovered. The embryogenic calli that were recovered were subcultured monthly for 6 months and tested for increased resistance to the temperature:time treatments previously determined to be lethal and to water stress as imposed by PEG. All of the selected cell lines were more resistant to both types of stress than the control cell lines. Leaf tissue of stress selected (Ro) formed and maintained callus growth when incubated at 38°C; whereas, tissue excised from nonselected controls rarely formed callus and calli which did form quickly became necrotic. These cells and plants will provide a tool for determining the mechanisms involved in resistance to high temperature stress.

Chronology of the differentiation of cotton (Gossypium hirsutum L.) fiber cells

Cotton fibers are single elongated cells that develop from epidermal cells of the ovule. The chronology of fiber differentiation was investigated using cultured ovules. Epidermal cells differentiate into fiber cells approx. 3 d before anthesis. When ovules were cultured on a defined medium, fiber growth could be initiated on ovules any time between 2 d preanthesis and the time of anthesis by adding indole-3-acetic acid and gibberellic acid to the medium. In the absence of phytohormones, fibers did not grow, and when ovules between 2 d preanthesis and anthesis were cultured without hormones past the day of anthesis and hormones then added, most ovules failed to produce fibers. The results define the timing of fiber differentiation from epidermal cells, and also define a window of time when differentiated cells are capable of further development. During this window, fiber cells are latent awaiting appropriate stimulation which in the intact plant is apparently associated with anthesis.

Somatic embryogenesis and plant regeneration in cotton (Gossypium hirsutum L.)

Tissue culture methods for improvement of cotton has lagged seriously compared to other major crops. A method for regeneration of cotton which includes a morphogenetically competent cell suspension was needed to facilitate selection of stress-resistant variants and gene manipulation. Preliminary screening of eight strains of Gossypium hirsutum L. for embryogenic potential resulted in the production of somatic embryos in all strains. Coker 312 was selected for use in the development of a model regeneration system for G. hirsutum. Calli were initiated from hypocotyl tissues of 3-day-old-seedlings. Globular embryos were present after six weeks in culture. Calli were subcultured to liquid suspension in growth regulator-free medium. After three to four weeks, suspensions were sieved to collect globular and heart stage embryos. Collected embryos developed further when plated onto semi-solid medium. To induce germination and plantlet growth, mature embryos were placed on sterile vermiculite saturated with medium. Upon development of roots and two true leaves, plantlets were potted in peat and sand, and hardened. Mature plants and progeny have been obtained with this procedure. A high percentage of infertile plants was observed among the regenerants.

Transformation of cotton (Gossypium hirsutum L.) by Agrobacterium tumefaciens and regeneration of transgenic plants

Cotton (Gossypium hirsutum L.) cotyledon tissues have been efficiently transformed and plants have been regenerated. Cotyledon pieces from 12-day-old aseptically germinated seedlings were inoculated with Agrobacterium tumefaciens strains containing avirulent Ti (tumor-inducing) plasmids with a chimeric gene encoding kanamycin resistance. After three days cocultivation, the cotyledon pieces were placed on a callus initiation medium containing kanamycin for selection. High frequencies of transformed kanamycin-resistant calli were produced, more than 80% of which were induced to form somatic embryos. Somatic embryos were germinated, and plants were regenerated and transferred to soil. Transformation was confirmed by opine production, kanamycin resistance, immunoassay, and DNA blot hybridization. This process for producing transgenic cotton plants facilitates transfer of genes of economic importance to cotton.

Somatic embryogenesis from leaf and petiole callus cultures of Gossypium hirsutum L

Leaf discs from four strains and petioles from six strains of Gossypium hirsutum were cultured on a variety of media. Callus formed from explants on all media, though embryogenesis was highly specific. Embryos formed from only three strain x media combinations. A small percentage of these embryos developed into plantlets. These results demonstrate that cotton plants can be obtained from leaf tissue explants.

Some characteristics of peroxidase secreted by cotton ovule cultures

Cotton (Gossypium hirsutum L.) ovule cultures secreted a soluble peroxidase into the surrounding medium, resulting in a 200-fold increase in this activity during the 30-day growth period. The peroxidase activity was thermostable from 4°C to 60°C and displayed a pH optimum of 5.5 to 6.0. The ovule peroxidase was susceptible to periodate treatment and very resistant to protease digestion. The data suggest that the peroxidase activity is a glycoprotein. Interpretation of peroxidase data may be complicated by the presence of phenol oxidase activity in the same preparations. The presence of phenol oxidases was ruled out by the inaction of a tyrosinase-specific inhibitor, tropolone.

Interspecific hybridization of perennial Medicago species using ovule-embryo culture

New interspecific hybrids between alfalfa (Medicago sativa L.) and several perennial Medicago species were obtained by embryo rescue techniques. The methodology, designated ovule-embryo culture, involved preculturing the fertilized ovule (10 to 20 days post-pollination) for a period of six to 12 days followed by excision and direct culture of the embryo. Placement of the hybrid embryo directly onto culture medium without the interim ovule culture was unsuccessful. Ovule culture to germination without removing the embryo also was unsuccessful. Ovule-embryo culture was essential for recovering interspecific hybrids between diploid alfalfa (2n=2x=16) and the following diploid (2n=2x=16) species: M. hybrida Traut., M. marina L., M. papillosa Boiss., M. rhodopea Velen. and M. rupestris M.B. In addition, trispecies hybrids between M. sativa x M. dzhawakhetica Bordz. F1 hybrids (2n=3x=24) and either M. cancellata M.B. (2n=6x=48) or M. saxatilis M.B. (2n=6x=48) were obtained from ovuleembryo culture. Media manipulations using M. sativa x M. rupestris F1 and first backcross generation embryos demonstrated the optimum concentration of 12.5 mM NH4 (+) for successful embryo rescue; ammonium salt formulation (whether chloride, nitrate or sulfate) was not critical. From a few thousand crosses, hybrids between M. sativa and either M. rhodopea or M. rupestris were recovered relatively efficiently with 157 and 66 hybrids, respectively. However, only 13 hybrids between M. sativa and M. papillosa were obtained from more than 2,000 crosses, and just two hybrids each have been recovered from the combinations M. sativa x M. hybrida and M. sativa x M. marina from 2,000 to 3,000 crosses. The predominant chromosome number between diploid alfalfa and the other diploid perennial species was 2n=2x=16. Morphology of the hybrids was generally intermediate. Electrophoretic analysis of the F1 hybrids and parental clones on uniform or gradient polyacrylamide gels demonstrated that peroxidase phenotypes could be used to confirm hybridity. For all interspecific combinations there was at least one peroxidase isozyme unique to the wild species that was present in the F1 interspecific hybrid.

Control of enzyme activities in cotton cotyledons during maturation and germination : III. In-vitro embryo development in the presence of abscisic acid

Cotton (Gossypium hirsutum L.) embryos excised from bolls 38-43 d after anthesis and cultured in vitro for 4 d on a nutrient agar medium containing 3.8 μM abscisic acid (ABA) developed enzyme activity and accumulated insoluble protein, neutral lipid, and dry weight similar to embryos maturing on the plant. Inclusion of ABA in the medium prevented precosious germination and allowed continued increases in catalase, malate dehydrogenase, citrate synthase, aspartate aminotransferase, and β-oxidation enzyme activities as well as de-novo synthesis of malate synthase. Isocitrate lyase activity was not detectable in ABA-cultured embryos nor normally-developed embryos. Omission of sucrose from the medium resulted in near-doubling of the development of malate synthase activity, with minimal effects on the other enzyme activities. Addition of Actinomycin D, cordycepin, or cycloheximide to ABA-containing cultures did not overcome the observed inhibition of germination, but severely reduced both the appearance of new malate synthase activity and further production of other related enzyme activities. Thus, development of these enzyme activities in the presence of ABA appears dependent on transcription and translation, while inhibition of germination by ABA at this stage of development is not sensitive to the RNA- and protein-synthesis inhibitors. The results indicate that ABA does not prevent vivipary by suppressing translation of m-RNAs coding for isocitrate lyase and its companion enzymes, as previously proposed.

Somatic embryogenesis in suspension cultures of Gossypium klotzschianum anderss

Somatic embryoids differentiated in suspension cultures of G. klotzschianum after 3-4 weeks of culture in a liquid medium containing glutamine (optimally, 10-15 mM). Embryogenesis occurred after a preculture of callus on a medium containing 10 mg/l of the cytokinin, 2iP. The embryoids had meristematic regions, a well formed epidermis, and formed roots and vestigial leaves. Asparagine was much less effective than glutamine in promoting embryoid differentiation. The presence of 2,4-D in the medium resulted in increased vigor of the suspension cultures and subsequently in the formation of many embryoids, but does not seem to be necessary for somatic embryogenesis in cotton.