Ginsenoside Production and Morphological Characterization of Wild Ginseng (Panax ginseng Meyer) Mutant Lines Induced by γ-irradiation ((60)Co) of Adventitious Roots

Production of specialized metabolites in plant cell and organo-cultures: the role of gamma radiation in eliciting secondary metabolism

PURPOSE

To provide an updated summary of recent advances in the application of gamma irradiation to elicit secondary metabolism and for induction of mutations in plant cell and organ cultures for the production of industrially important specialized metabolites (SMs).

CONCLUSIONS

Research on the application of gamma radiation with plants has contributed a lot to microbial decontamination of seeds, and the promotion of physiological processes such as seed germination, seedling vigor, plant growth, and development. Various studies have demonstrated the influence of gamma rays on the morphology, physiology, and biochemistry of plants. Recent research efforts have also shown that low-dose gamma (5-100 Gy) irradiation can be utilized as an expedient solution to alleviate the deleterious effect of abiotic stresses and to obtain better yields of plants. Inducing mutagenesis using gamma irradiation has also evolved as a better option for inducing genetic variability in crops, vegetables, medicinal and ornamentals for their genetic improvement. Plant SMs are gaining increasing importance as pharmaceutical, therapeutic, cosmetic, and agricultural products. Plant cell, tissue, and organ cultures represent an attractive alternative to conventional methods of procuring useful SMs. Among the varied approaches the elicitor-induced in vitro culture techniques are considered an efficient tool for studying and improving the production of SMs. This review focuses on the utilization of low-dose gamma irradiation in the production of high-value SMs such as phenolics, terpenoids, and alkaloids. Furthermore, we present varied successful examples of gamma-ray-induced mutations in the production of SMs.

The Impact of Acute Low-Dose Gamma Irradiation on Biomass Accumulation and Secondary Metabolites Production in Cotinus coggygria Scop. and Fragaria × ananassa Duch. Red Callus Cultures

Cotinus coggygria Scop. (smoketree) and Fragaria × ananassa Duch. (strawberry) are two industrially important species due to their composition in bioactive compounds. In this study, we investigated the effects of acute low-dose gamma irradiation (15, 20, 25, 30, 35 and 40 Gy) on two red callus cultures established in smoketree and strawberry. The biomass production, dry weight, content of phenols, flavonoids, monomeric anthocyanins', index of anthocyanins polymerization and antioxidant activity were evaluated. For the smoketree callus, a negative correlation between irradiation doses and callus biomass accumulation was observed. For the strawberry callus, irradiation did not significantly affect the accumulation of the biomass. An increased dry weight was observed in irradiated smoketree callus, while for treated strawberry callus, a decrease was recorded. Irradiation with 30 Gy was stimulative for polyphenols' accumulation in both cultures; however, the increase was significant only in the strawberry callus. The flavonoids increased in the 30 Gy strawberry variants, while it significantly decreased in smoketree callus irradiated with 35 and 40 Gy. In irradiated strawberry callus, except for the 25 Gy variant (1.65 ± 0.4 mg C-3-GE/g DW), all treatments caused an increase in anthocyanins' accumulation. In smoketree, except for the 15 Gy variant (2.14 ± 0.66 mg C-3-GE/g DW), the irradiation determined an increase in anthocyanins synthesis, with the highest value being seen in the 20 Gy variant (2.8 ± 0.94 mg C-3-GE/g DW). According to UPLC-HRMS investigations, an unidentified compound increased by 99% at the 30 Gy dose in strawberry callus, while in smoketree, maslinic acid increased by 51% after irradiation with 40 Gy. The results of this study showed, for the first time, the differential response of two performant callus cultures to low-dose gamma irradiation, a biotechnological method that can be used to stimulate the synthesis of important flavonoids and triterpenes.

Akt activation-dependent protective effect of wild ginseng adventitious root protein against UVA-induced NIH-3T3 cell damage

Prolonged skin exposure to ultraviolet radiation can lead to development of several acute and chronic diseases, with UVA exposure considered a primary cause of dermal photodamage. We prepared a wild ginseng adventitious root extract (ARE) that could alleviate UVA irradiation-induced NIH-3T3 cell viability decline. After employing a series of purification methods to isolate main active components of ARE, adventitious root protein mixture (ARP) was identified then tested for protective effects against UVA irradiation-induced NIH-3T3 cell damage. The results showed that ARP treatment significantly reduced UVA-induced cell viability decline and confirmed that the active constituent of ARP was the protein, since proteolytic hydrolysis and heat treatment each eliminated ARP protective activity. Moreover, ARP treatment markedly inhibited UVA-induced apoptosis, cell cycle arrest and DNA fragmentation, while also significantly reversing UVA effects (elevated Bax levels, reduced Bcl-2 expression) by reducing Bax levels and increasing Bcl-2 expression. Mechanistically, ARP promoted Akt phosphorylation regardless of UVA exposure, thus confirming ARP resistance to inactivation by UVA light. Notably, in the presence of Akt inhibitor SC0227, ARP could no longer counteract UVA-induced cell viability decline and DNA fragmentation. Additionally, our results demonstrated that ARP treatment protected UVA-irradiated NIH-3T3 cells by preventing UVA-induced reduction of collagen-I expression. Taken together, these results suggest that ARP treatment of NIH-3T3 cells effectively mitigated UVA-induced cell viability decline by activating intracellular Akt to reduce UVA-induced DNA damage, leading to reduced rates of apoptosis and cell cycle arrest after UVA exposure and restoring collagen expression to normal levels.

Phytochemistry of ginsenosides: Recent advancements and emerging roles

Ginsenosides, a group of tetracyclic saponins, accounts for the nutraceutical and pharmaceutical relevance of the ginseng (Panax sp.) herb. Owing to the associated therapeutic potential of ginsenosides, their demand has been increased significantly in the last two decades. However, a slow growth cycle, low seed production, and long generation time of ginseng have created a gap between the demand and supply of ginsenosides. The biosynthesis of ginsenosides involves an intricate network of pathways with multiple oxidation and glycosylation reactions. However, the exact functions of some of the associated genes/proteins are still not completely deciphered. Moreover, ginsenoside estimation and extraction using analytical techniques are not feasible with high efficiency. The present review is a step forward in recapitulating the comprehensive aspects of ginsenosides including their distribution, structural diversity, biotransformation, and functional attributes in both plants and animals including humans. Moreover, ginsenoside biosynthesis in the potential plant sources and their metabolism in the human body along with major regulators and stimulators affecting ginsenoside biosynthesis have also been discussed. Furthermore, this review consolidates biotechnological interventions to enhance the biosynthesis of ginsenosides in their potential sources and advancements in the development of synthetic biosystems for efficient ginsenoside biosynthesis to meet their rising industrial demands.

Biomass accumulation of Panax vietnamensis in cell suspension cultures varies with addition of plant growth regulators and organic additives

OBJECTIVE

To evaluate the impact of plant growth regulators including kinetin (KN), benzyl adenine and naphthalene acetic acid, yeast extract and casein hydrolyzate on biomass accumulation of Vietnamese ginseng Panax vietnamensis (P. vietnamensis) in cell suspension culture.

METHODS

Cell suspension cultures were established from friable calluses derived from leaves and petioles of 3-year-old in-vitro P. vietnamensis plants. The cell suspension cultures were grown in Murashige and Skoog basal media supplemented with various concentrations of KN, benzyl adenine, naphthalene acetic acid, and yeast extract and casein hydrolyzate.

RESULTS

All tested factors generated an increase in the cell biomass of P. vietnamensis in suspension culture, but the impact of each varies depended on the factor type, concentration, and incubation period. Addition of 2.0 mg/L KN resulted in the largest biomass increase after 24 d, (57.0 ± 0.9) and (3.1 ± 0.1) mg/mL fresh and dry weight, respectively, whereas addition of benzyl adenine or naphthalene acetic acid produced optimum levels of Panax cell biomass at 1.0 and 1.5 mg/L, respectively. Addition of the elicitor yeast extract led to a 1.4-2.4 fold increase in biomass of P. vietnamensis, while addition of casein hydrolyzate enhanced biomass accumulation 1.8-2.6 fold.

CONCLUSIONS

The addition of each factor causes significant changes in biomass accumulation of P. vietnamensis. The largest biomass accumulation is from cultures grown in MS media containing 2.0 mg/L KN for 24 d. The outcome of the present study provides new insights into the optimal suspension culture conditions for studies on the in vitro cell biomass production of P. vietnamensis.

Gamma irradiation of medicinally important plants and the enhancement of secondary metabolite production

PURPOSE

The profitable production of some important plant-based secondary metabolites (ginsenosides, saponins, camptothecin, shikonins etc.) in vitro by gamma irradiation is a current area of interest. We reviewed different types of secondary metabolites, their mode of synthesis and effect of γ-radiation on their yield for different plants, organs and in vitro cultures (callus, suspension, hairy root). Special effort has been made to review the biochemical mechanisms underlying the increase in secondary metabolites. A comparison of yield improvement with biotic and abiotic stresses was made.

RESULTS

Phenolic compounds increase with γ-irradiation in whole plants/plant parts; psoralen content in the common herb babchi (Psoralea corylifolia) was increased as high as 32-fold with γ-irradiation of seeds at 20 kGy. The capsaicinoids, a phenolic compound increased about 10% with 10 kGy in paprika (Capsicum annum L.). The in vitro studies show all the three types of secondary metabolites are reported to increase with γ-irradiation. Stevioside, total phenolic and flavonoids content were slightly increased in 15 Gy-treated callus cultures of stevia (Stevia rebaudiana Bert.). In terpenoids, total saponin and ginsenosides content were increased 1.4- and 1.8-fold, respectively, with 100 Gy for wild ginseng (Panax ginseng Meyer) hairy root cultures. In alkaloids, camptothecin yield increased as high as 20-fold with 20 Gy in callus cultures of ghanera (Nothapodytes foetida). Shikonins increased up to 4-fold with 16 Gy in suspension cultures of purple gromwell (Lithospermum erythrorhizon S.). The enzymes associated with secondary metabolite production were increased with γ-irradiation of 20 Gy; namely, phenylalanine ammonia-lyase (PAL) for phenolics, chalcone synthase (CHS) for flavonoids, squalene synthase (SS), squalene epoxidase (SE) and oxidosqualene cyclases (OSC) for ginsenosides and PHB (p-hydroxylbenzoic acid) geranyl transferase for shikonins.

CONCLUSIONS

An increase in secondary metabolites in response to various biotic and abiotic stresses is compared with ionizing radiation. A ∼5- to 20-fold increase is noted with ∼20 Gy irradiation dose. It increases the yield of secondary metabolites by enhancing the activity of certain key biosynthetic enzymes. Identification of the optimum dose is the important step in the large-scale production of secondary metabolites at industrial level.

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.

Karyotype analysis of Panax ginseng C.A.Meyer, 1843 (Araliaceae) based on rDNA loci and DAPI band distribution

Ginseng has long been considered a valuable plant owing to its medicinal properties; however, genomic information based on chromosome characterization and physical mapping of cytogenetic markers has been very limited. Dual-color FISH karyotype and DAPI banding analyses of Panax ginseng C. A. Meyer, 1843 were conducted using 5S and 45S rDNA probes. The somatic chromosome complement was 2n=48 with lengths from 3.3 μm to 6.3 μm. The karyotype was composed of 12 metacentric, 9 submetacentric, and 3 subtelocentric pairs. The 5S rDNA probe localized to the intercalary region of the short arm of pair 11, while the 45S rDNA was located at the secondary constriction of the subtelocentric satellited chromosome 14. DAPI bands were clearly observed for most chromosomes, with various signal intensities and chromosomal distributions that consequently improved chromosome identification. As a result, all 24 chromosomes could be distinguished and numbers were assigned to each chromosome for the first time. The results presented here will be useful for the on-going ginseng genome sequencing and further molecular-cytogenetic studies and breeding programs of ginseng.