Elicitation of silymarin in cell cultures of Silybum marianum: effect of subculture and repeated addition of methyl jasmonate

Bioreactor configurations for adventitious root culture: recent advances toward the commercial production of specialized metabolites

In vitro plant cell and organ cultures are appealing alternatives to traditional methods of producing valuable specialized metabolites for use as: pharmaceuticals, food additives, cosmetics, perfumes, and agricultural chemicals. Cell cultures have been adopted for the production of specialized metabolites in certain plants. However, in certain other systems, adventitious roots are superior to cell suspension cultures as they are organized structures that accumulate high levels of specialized metabolites. The cultivation of adventitious roots has been investigated in various bioreactor systems, including: mechanically agitated, pneumatically agitated, and modified bioreactors. The main relevance and importance of this work are to develop a long-lasting industrial biotechnological technology as well as to improve the synthesis of these metabolites from the plant in vitro systems. These challenges are exacerbated by: the peculiarities of plant cell metabolism, the complexity of specialized metabolite pathways, the proper selection of bioreactor systems, and bioprocess optimization. This review's major objective is to analyze several bioreactor types for the development of adventitious roots, as well as the advantages and disadvantages of each type of bioreactor, and to describe the strategies used to increase the synthesis of specialized metabolites. This review also emphasizes current advancements in the field, and successful instances of scaled-up cultures and the generation of specialized metabolites for commercial purposes are also covered.

Verbascoside production in long-term Buddleja cordata Kunth cell suspension cultures

Previously, our group reported the establishment of a white callus cell line of Buddleja cordata Kunth that is a high producer of the secondary metabolite, verbascoside (VB, also named acteoside), under suspension culture conditions. Here, we present experimental evidence of the sustained ability of that cellular line to grow and produce high amounts of VB for 5 years of continuous culture. Cellular line profiles were determined at the early (at the beginning) and late stages (at the end of 5 years of continuous subculturing) by analyzing relevant parameters of culture growth, i.e., specific growth rate [µ], doubling time [dt], and growth index [GI], as well as VB production. Late-stage cultures exhibited a 61% faster growth rate than early-stage subcultures, and 25 and 3% lower doubling time and growth index. The extents of growth phases were found to be different. Similar amounts of biomass were found (9.5 g and 9.4 g L-1). Verbascoside production increased parallel to cell growth; maximal yield level occurred in the mid-exponential phase and lasted until the end of the stationary phase (i.e., from the 15th to the 25th day and from the 9th to the 21st day for the early and late stages, correspondingly). The content of VB was higher in the late-stage culture (1.43 ± 0945 g L-1) than in the early-stage culture (1.21 ± 0.0286 g L-1). Productivity values point out the potential use of B. cordata cell line in the biotechnological production of VB and for research focused on the biochemistry of secondary metabolism.

In vitro culture, transformation and genetic fidelity of Milk Thistle

This review article presents a consolidated explanation and provides a comprehensive description of various studies, carried out on in vitro culture and hairy root cultures of S. marianum which can be consider an alternative source of flavonolignans. To overcome the constrains of conventional propagation of silybum plant, tissue culture and advanced biotechnology proved to be an influential tool that can complement conventional breeding and accelerate silybum development. The present review is focused on biotechnological tools like in vitro culture, hairy root cultures and genetic fidelity of S. marianum which can be a potent tool for production of secondary metabolites from these cultures.

A comparative study of biotechnological approaches for producing valuable flavonoids in Prosopis farcta

The callus and hairy root cultures of Prosopis farcta were established to develop effective strategies to enhance its valuable and medicinally important flavonoid compounds. For callus induction, the hypocotyl, cotyledon and shoot explants were subjected to different plant hormones, naphthalene acetic acid (NAA), benzylaminopurine (BAP), kinetin and dichlorophenoxyacetic acid (2,4-D). Greater callus induction was obtained from hypocotyl explants on MS medium containing 3.0 mg L^-1 NAA + 2.0 mg L^-1 BAP. With the addition of 0.5 mg L^-1 asparagine to this medium, the maximum callus growth was achieved. Hairy root culture of P. farcta was performed using transformation of different explants with strains of Agrobacterium rhizogenes LBA9404, A4, AR15834. The AR15834 strain was more effective for hairy root induction where it caused hairy root formation on 59% of the infected cotyledon explants. We compared profiles of flavonoids isolated from seedling roots, hairy roots, and callus cultures of P. farcta. The colorimetric analysis showed that the content of total flavonoids of hairy roots was 1.54 and 2.52 times higher than in seedling roots and callus, respectively. The presence of flavonoids was verified by LC/MS in positive ion mode. The results showed that flavonoid composition was different in the roots and callus. Naringenin was the major constituent in callus, whereas resveratrol, quercetin and myricetin were the most abundant compounds found in hairy roots. The main objective of this research was to establish hairy roots in P. farcta to synthesize flavonoids at levels comparable to in vitro-grown roots. The present study also opens up a way to further improve the production of pharmaceutically valuable flavonoids and to produce desired metabolites using the hairy root culture system.

Enhancement of silymarin and phenolic compound accumulation in tissue culture of Milk thistle using elicitor feeding and hairy root cultures

In the present study, the effects of the metabolite elicitors chitosan, methyl jasmonate (MeJA) and salicylic acid (SA) as well as the hairy root transformation were tested for silymarin and phenolic compound accumulation in in vitro cultures of Milk thistle. For callus induction, leaf explants were cultured on MS medium supplemented with 5 mg/l NAA + 2 mg/l Kin + 0.1 mg/l GA3. Chitosan, SA and MeJA were added separately in three concentrations 200, 400 and 800 mg/l; 10, 20 and 40 mg/l; 20, 40 and 80 mg/l, respectively, to hormone free B5 medium. Alternatively, cotyledons of 12 day old seedlings were transformed with Agrobacterium rhizogenes A4 strain. Overall, increasing the concentrations of the three elicitors dramatically increased the total silymarin content. Remarkably, the elicitors mainly enhanced the accumulation of silybine A&B that were not detected in un-treated callus culture (control). In addition, the hairy root culture triggered the accumulation of silybine A&B, and silydianin, which was not detected in the non-transgenic roots. The hairy root culture was superior in production of the phenolic compounds in comparison to the control and elicitor treatments. The hairy root cultures showed also higher antioxidant capacities than non-transformed cultures and/or chemically elicited-callus cultures. Thus hairy root provide instrumental in enhancing the production of economically valuable metabolite.

Phosphoglycerolipids are master players in plant hormone signal transduction

Phosphoglycerolipids are essential structural constituents of membranes and some also have important cell signalling roles. In this review, we focus on phosphoglycerolipids that are mediators in hormone signal transduction in plants. We first describe the structures of the main signalling phosphoglycerolipids and the metabolic pathways that generate them, namely the phospholipase and lipid kinase pathways. In silico analysis of Arabidopsis transcriptome data provides evidence that the genes encoding the enzymes of these pathways are transcriptionally regulated in responses to hormones, suggesting some link with hormone signal transduction. The involvement of phosphoglycerolipid signalling in the early responses to abscisic acid, salicylic acid and auxins is then detailed. One of the most important signalling lipids in plants is phosphatidic acid. It can activate or inactivate protein kinases and/or protein phosphatases involved in hormone signalling. It can also activate NADPH oxidase leading to the production of reactive oxygen species. We will interrogate the mechanisms that allow the activation/deactivation of the lipid pathways, in particular the roles of G proteins and calcium. Mediating lipids thus appear as master players of cell signalling, modulating, if not controlling, major transducing steps of hormone signals.

Improved silymarin content in elicited multiple shoot cultures of Silybum marianum L

Silybum marianum L. extracts are being used as antihepatotoxic therapy for liver diseases. Silymarin is a polyphenolic flavonoid mixture isolated from milk thistle which is believed to be responsible for the plant's hepatoprotective action. Regeneration of Silybum marianum plants from shoot tip explants and assessment of their morphogenic potential, silymarin total concentration and its major constituents upon exposure to medium composition alteration and different elicitors' application was targeted. Different concentrations of NaCl, quercetin, gamma irradiation and dried fungal extracts were used to elicit silymarin production in the cultures. The chemical composition of silymarin and its total concentration was investigated through HPLC at all the experiment stages. Multiple shoots were recorded after 3 weeks of culture on MS medium containing various concentrations of BA and/or NAA. IAA was more effective than NAA and IBA in inducing robust roots in shoot cultures. The flowering plants recorded 20 % and 40 % of the total plants number in the multiplication and rooting stages respectively. The highest total silymarin concentration reached its peak with (10 Gy) gamma-irradiation to be 6.598 % dry weight in the in vitro regenerated shoot tip explants. The in vitro grown flowers showed 1.7 times more sylimarin productivity as compared to that of the wild grown congruent.

Recent advances towards development and commercialization of plant cell culture processes for the synthesis of biomolecules

Plant cell culture systems were initially explored for use in commercial synthesis of several high-value secondary metabolites, allowing for sustainable production that was not limited by the low yields associated with natural harvest or the high cost associated with complex chemical synthesis. Although there have been some commercial successes, most notably paclitaxel production from Taxus sp., process limitations exist with regards to low product yields and inherent production variability. A variety of strategies are being developed to overcome these limitations including elicitation, in situ product removal and metabolic engineering with single genes and transcription factors. Recently, the plant cell culture production platform has been extended to pharmaceutically active heterologous proteins. Plant systems are beneficial because they are able to produce complex proteins that are properly glycosylated, folded and assembled without the risk of contamination by toxins that are associated with mammalian or microbial production systems. Additionally, plant cell culture isolates transgenic material from the environment, allows for more controllable conditions over field-grown crops and promotes secretion of proteins to the medium, reducing downstream purification costs. Despite these benefits, the increase in cost of heterologous protein synthesis in plant cell culture as opposed to field-grown crops is significant and therefore processes must be optimized with regard to maximizing secretion and enhancing protein stability in the cell culture media. This review discusses recent advancements in plant cell culture processing technology, focusing on progress towards overcoming the problems associated with commercialization of these production systems and highlighting recent commercial successes.