High Frequency of Plant Regeneration through Cyclic Secondary Somatic Embryogenesis in Panax ginseng

In Vitro Cultivation and Ginsenosides Accumulation in Panax ginseng: A Review

The use of in vitro tissue culture for herbal medicines has been recognized as a valuable source of botanical secondary metabolites. The tissue culture of ginseng species is used in the production of bioactive compounds such as phenolics, polysaccharides, and especially ginsenosides, which are utilized in the food, cosmetics, and pharmaceutical industries. This review paper focuses on the in vitro culture of Panax ginseng and accumulation of ginsenosides. In vitro culture has been applied to study organogenesis and biomass culture, and is involved in direct organogenesis for rooting and shooting from explants and in indirect morphogenesis for somatic embryogenesis via the callus, which is a mass of disorganized cells. Biomass production was conducted with different types of tissue cultures, such as adventitious roots, cell suspension, and hairy roots, and subsequently on a large scale in a bioreactor. This review provides the cumulative knowledge of biotechnological methods to increase the ginsenoside resources of P. ginseng. In addition, ginsenosides are summarized at enhanced levels of activity and content with elicitor treatment, together with perspectives of new breeding tools which can be developed in P. ginseng in the future.

Efficient Somatic Embryogenesis, Regeneration and Acclimatization of Panax ginseng Meyer: True-to-Type Conformity of Plantlets as Confirmed by ISSR Analysis

Panax ginseng Meyer grows in east Russia and Asia. There is a high demand for this crop due to its medicinal properties. However, its low reproductive efficiency has been a hindrance to the crop's widespread use. This study aims to establish an efficient regeneration and acclimatization system for the crop. The type of basal media and strength were evaluated for their effects on somatic embryogenesis, germination, and regeneration. The highest rate of somatic embryogenesis was achieved for the basal media MS, N6, and GD, with the optimal nitrogen content (≥35 mM) and NH₄⁺/NO₃^- ratio (1:2 or 1:4). The full-strength MS medium was the best one for somatic embryo induction. However, the diluted MS medium had a more positive effect on embryo maturation. Additionally, the basal media affected shooting, rooting, and plantlet formation. The germination medium containing 1/2 MS facilitated good shoot development; however, the medium with 1/2 SH yielded outstanding root development. In vitro-grown roots were successfully transferred to soil, and they exhibited a high survival rate (86.3%). Finally, the ISSR marker analysis demonstrated that the regenerated plants were not different from the control. The obtained results provide valuable information for a more efficient micropropagation of various P. ginseng cultivars.

Efficacy of Panax ginseng Meyer Herbal Preparation HRG80 in Preventing and Mitigating Stress-Induced Failure of Cognitive Functions in Healthy Subjects: A Pilot, Randomized, Double-Blind, Placebo-Controlled Crossover Trial

Background: The aim of this pilot study was to compare the efficacy of hydroponically cultivated red Panax ginseng Meyer root preparation (HRG80) and traditionally harvested six-year-old white P. ginseng standard preparation (PGS) with placebo in preventing symptoms of stress. Methods: The effects of HRG80, PGS, and placebo capsules were studied in 50 tired healthy subjects in a three-arm, randomized, double-blinded, placebo-controlled crossover trial. Efficacy-outcome measures included the accuracy of processing the d2 test for cognitive functions, obtained accuracy score in a computerized memory test, and the perceived-stress (PS) score. Results: A statistically significant interaction effect between time and treatment (p < 0.0001) was observed in the attention d2 and memory tests, indicating that HRG80 treatment was more beneficial than that with a placebo. The effects of PGS were better than those of the placebo, but the difference was not statistically significant. There was significant difference between the effects of HRG80 and PGS (p < 0.0001) that were observed after single (Day 1) and repeated administrations on Days 5 and 12 of treatment. Conclusion: Overall, HRG80 treatment was significantly superior compared to that with the PGS and placebo regarding attention, memory, and PS scores after single and repeated administrations for 5 and 12 days.

Functional characterization of a WRKY family gene involved in somatic embryogenesis in Panax ginseng

As a perennial herbaceous species, Panax ginseng is widely cultivated and used as traditional herbal medicine. The root of Panax ginseng commonly remains expensive as conventional breeding of Panax ginseng is difficult. Somatic embryogenesis (S.E.) is a useful tool for plant propagation and optimal model for understanding the mechanisms of plant embryogenesis. In Panax ginseng, increasing studies have been widely performed to optimize the technology of S.E., while the underlying mechanism remains unclear. In this paper, we cloned and identified a WRKY family gene named PgWRKY6 which is upregulated in response to 2,4-D (2,4-dichlorophenoxyacetic acid)-induced embryogenic callus development. The silencing of PgWRKY6 obviously reduces the induction rate of embryogenic callus, indicating its crucial role in S.E. of Panax ginseng hairy root. The expressions of several ROS-scavenging genes are also inducible during embryogenic callus development, and the transcriptions of PgGST, PgAPX1, and PgSOD are demonstrated to be regulated by PgWRKY6. Recombinant PgWRKY6, an approximate 40-KDa protein purified from Escherichia coli, shows a specific DNA-binding activity with a potential recognition site of TTGAC(C/T). This work demonstrated that as a conserved WRKY family transcription factor, PgWRKY6 functions upstream of PgGST, PgAPX1, and PgSOD, and potentially mediated auxins -ROS signaling pathway in the process of S.E. in Panax species.

Genome size analysis of field grown and somatic embryo regenerated plants in Allium sativum L

In the present study, an efficient in vitro propagation protocol has been developed from clove explants of Allium sativum L., one of the oldest vegetable and medicinal plant used worldwide. Garlic is propagated vegetatively as cross-fertilization is strictly precluded due to sterile flowers. Due to a low rate of multiplication, limited genetic improvement possibility and increased germplasm degradation, plant tissue culture becomes an efficient and preferred tool for quality and rapid propagation of garlic. Here, the clove explants were cultured on Murashige and Skoog basal medium amended with different concentrations of Plant Growth Regulators (PGRs) namely 2,4-dichlorophenoxy acetic acid (2,4-D), 6-benzyl amino purine (BAP), and 1-naphthalene acetic acid (NAA). Within 2 weeks of inoculation, white compact callus was formed, maximum callus induction frequency (85.99%) was on 1.5 mg l^-1 2, 4-D added MS medium. Induced callus transformed into an embryogenic callus on 2, 4-D and BAP amended MS medium with highest embryogenic frequency (77.7%) was noted on 0.25 mg l^-1 2, 4-D and 1.0 mg l^-1 BAP added medium. Embryogenic callus differentiated into progressive stages of somatic embryos starting from globular, scutellar, and finally to coleoptilar stage of the embryo. Histological and scanning electron microscopic study of embryogenic callus was conducted, showing different stages of embryos, their origin and development, re-confirming somatic embryogenesis incidence in A. sativum. Green and mature somatic embryos were germinated and converted into plantlets on 0.5 mg l^-1 BAP amended MS medium. The in vitro regenerated plants were cultured separately in IBA and NAA supplemented media for root induction. The MS medium amended with 1.0 mg l^-1 IBA proved to be the best PGR treatment in inducing roots. The rooted plants were acclimatized and transferred ex vitro with about 87% survival rate. Cytological and flow cytometric analyses were performed to assess the genetic stability of in vitro regenerated plants. Cytological studies of in vitro regenerated plants showed 2n = 16 chromosome number and did not reveal any numerical variation in chromosomes. Flow cytometry was employed to measure the 2C DNA content of somatic embryo regenerated A. sativum plants and compared with in vivo grown garlic. The histogram peaks of relative 2C DNA content of in vitro regenerated plantlets were similar to the corresponding 2C DNA peak of in vivo grown plants. Flow cytometric 2C DNA content of embryo regenerated and field-grown A. sativum plants were the same, i.e., 33.45 pg and 33.56 pg, respectively, confirming genetic similarity. In conclusion, the present cytological and flow cytometric study suggest that the in vitro culture conditions are quite safe, did not encourage genetic alterations, and regenerants were "true to type."

Plant regeneration through somatic embryogenesis and genome size analysis of Coriandrum sativum L

In the present study, an improved plant regeneration protocol via primary and secondary somatic embryogenesis was established in two Co-1 and Rajendra Swathi (RS) varieties of Coriandrum sativum L. Callus was induced from root explants on 2, 4-D (0.5-2.0 mg/l) supplemented MS. The addition of BA (0.2 mg/l) improved callus induction and proliferation response significantly. The maximum callus induction frequency was on 1.0 mg/l 2, 4-D and 0.2 mg/l BA added MS medium (77.5 % in Co-1 and 72.3 % in RS). The callus transformed into embryogenic callus on 2, 4-D added MS with maximum embryogenic frequency was on 1.0 mg/l. The granular embryogenic callus differentiated into globular embryos on induction medium, which later progressed to heart-, torpedo- and cotyledonary embryos on medium amended with 0.5 mg/l NAA and 0.2 mg/l BA. On an average, 2-3 secondary somatic embryos (SEs) were developed on mature primary SEs, which increased the total embryo numbers in culture. Histology and scanning electron microscopy (SEM) studies are presented for the origin, development of primary and secondary embryos in coriander. Later, these induced embryos converted into plantlets on 1.0 mg/l BA and 0.2 mg/l NAA-amended medium. The regenerated plantlets were cultured on 0.5 mg/l IBA added ½ MS for promotion of roots. The well-rooted plantlets were acclimatized and transferred to soil. The genetic stability of embryo-regenerated plant was analyzed by flow cytometry with optimized Pongamia pinnata as standard. The 2C DNA content of RS coriander variety was estimated to 5.1 pg; the primary and secondary somatic embryo-derived plants had 5.26 and 5.44 pg 2C DNA content, respectively. The regenerated plants were genetically stable, genome size similar to seed-germinated coriander plants.

In vitro grown thickened taproots, a new type of soil transplanting source in Panax ginseng

BACKGROUND

The low survival rate of in vitro regenerated Panax ginseng plantlets after transfer to soil is the main obstacle for their successful micropropagation and molecular breeding. In most cases, young plantlets converted from somatic embryos are transferred to soil.

METHODS

In vitro thickened taproots, which were produced after prolonged culture of ginseng plantlets, were transferred to soil.

RESULTS

Taproot thickening of plantlets occurred near hypocotyl and primary roots. Elevated concentration of sucrose in the medium stimulated the root thickening of plantlets. Senescence of shoots occurred following the prolonged culture of plantlets. Once the leaves of plantlets senesced, the buds on taproots developed a dormant tendency. Gibberellic acid treatment was required for dormancy breaking of the buds. Analysis of endogenous abscisic acid revealed that the content of abscisic acid in taproots with senescent shoots was comparatively higher than that of taproots with green shoots. Thickened taproots were transferred to soil, followed by exposure to gibberellic acid or a cold temperature of 2°C for 4 mo. Cold treatment of roots at 2°C for 4 mo resulted in bud sprouting in 84% of roots. Spraying of 100 mg/L gibberellic acid also induced the bud sprouting in 81% roots.

CONCLUSION

Soil transfer of dormant taproots of P. ginseng has advantages since they do not require an acclimatization procedure, humidity control of plants, and photoautotrophic growth, and a high soil survival rate was attained.

Plant regeneration of Korean wild ginseng (Panax ginseng Meyer) mutant lines induced by γ-irradiation ((60)Co) of adventitious roots

An efficient in vitro protocol has been established for somatic embryogenesis and plantlet conversion of Korean wild ginseng (Panax ginseng Meyer). Wild-type and mutant adventitious roots derived from the ginseng produced calluses on Murashige and Skoog (MS) medium supplemented with 0.5 mg/L 2,4-dichlorophenoxyacetic acid and 0.3 mg/L kinetin; 53.3% of the explants formed callus. Embryogenic callus proliferation and somatic embryo induction occurred on MS medium containing 0.5 mg/L 2,4-dichlorophenoxyacetic acid. The induced somatic embryos further developed to maturity on MS medium with 5 mg/L gibberellic acid, and 85% of them germinated. The germinated embryos were developed to shoots and elongated on MS medium with 5 mg/L gibberellic acid. The shoots developed into plants with well-developed taproots on one-third strength Schenk and Hildebrandt basal medium supplemented with 0.25 mg/L 1-naphthaleneacetic acid. When the plants were transferred to soil, about 30% of the regenerated plants developed into normal plants.