Anthraquinones as phytoalexins in cell and tissue cultures of Cinchona spec

Degradation of antifungal anthraquinone compounds is a probable physiological role of DyP secreted by Bjerkandera adusta

Alizarin is an anti-fungal compound produced by the plant, Rubia tinctorum. The parasitic fungus Bjerkandera adusta Dec 1 was cultured in potato dextrose (PD) medium with or without alizarin. Alizarin was a good substrate for the dye-decolorizing peroxidase (DyP) from B. adusta Dec 1 and hampered B. adusta growth at the early stage of plate culture. During liquid shaking culture, DyP activity in cultures supplemented with 100 μM alizarin was greater than that in controls cultured without alizarin. In particular, DyP activity per dry cell mass increased approximately 3.5-, 3.1-, and 2.9-fold at 24, 30, and 36 h after inoculation, respectively, compared with control cultures. These data suggest that alizarin stimulates the expression of DyP. Interestingly, alizarin rapidly decomposed at an early stage in culture (24–42 h) in PD medium supplemented with 100 μM alizarin. Thus, alizarin appears to induce DyP expression in B. adusta Dec 1, and this DyP, in turn, rapidly degrades alizarin. Collectively, our findings suggest that the physiological role of DyP is to degrade antifungal compounds produced by plants.

Detrimental effects ofCinchona leaf alkaloids on larvae of the polyphagous insectSpodoptera exigua

YoungCinchona ledgeriana plants contain two types of alkaloid: indole alkaloids in the leaves and quinoline alkaloids in the root. FromCinchona leaves, a crude alkaloid extract was made, containing the cinchophylline type of indole alkaloids and a small amount of 5-methoxytryptamine. The leaf alkaloid extract exerted a strong detrimental effect on the growth of larvae of the polyphagous beet armyworm,Spodoptera exigua (Lepidoptera). Feeding of larvae on an artificial diet containing the leaf alkaloids at the same concentrations as those found in the plant resulted in significant growth reduction, retardation in development, and mortality of the larvae. Cinchophyllines are composed of 5-methoxytryptamine coupled to a corynantheal unit. When incorporated into the artificial diet, 5-methoxytryptamine alone had no effect on the 5.exigua larvae. Corynantheal, however, had a strong detrimental effect on growth of the larvae, its effect being comparable to that of the leaf alkaloid extract. In contrast to the indole-type leaf alkaloids, the quinolinetypeCinchona root alkaloids did not affect growth and development of the larvae. These results suggest that the indole-type alkaloids, which inCinchona plants are present at the highest concentrations in the young, vulnerable leaflets, are involved in the chemical defense of the plant against herbivorous insects.

A novel membrane reactor design for controlled studies of interacting populations (simulation of the interaction between microorganism and plant suspension cultures)

The design of a reactor in which two interacting cell populations (microorganisms and plants) could grow under controlled conditions was considered. In this reactor, the cell populations are separated by a membrane which permits semi-in vivo study of induced interaction-specific changes in metabolism. In this paper, the interaction of suspension culture of Nicotiana tabacum (tobacco) and the Oomycete, Phytophthora nicotiana was simulated. The results of the computer simulation show the induced metabolic changes as a consequence of the biological interaction. The paper introduces a novel approach in the strategy for the study of interacting population in suspension cultures. This type of system has potential applications in studies of the regulation of secondary metabolism and for the production of high values pharmaceuticals. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 609-615, 1997.

Anthraquinone distribution in the hypogeal apparatus of Rubia peregrina L. growing wild in Sardinia

The isolation, characterisation and quantification of anthraquinones, from hypogeal apparatus of Rubia peregrina L. (Wild Madder) growing wild in Sardinia (Italy) are described. The present study allowed us to perform an easy and fast HPLC analytical method for the detection of anthraquinones in all underground parts of plant. Concentrations of these compounds are variable in the different hypogeal parts before and after hydrolysis of the crude methanolic extracts. Before hydrolysis, we found that pseudopurpurin was 0.18% in rhizomes, alizarin 0.02% in rhizomes and principal stolons, and purpurin 0.56% in stolons of second order. Rubiadin is the major constituent of R. peregrina and reached a higher concentration in principal stolons of up to 4.8%. After hydrolysis, we found some drastic changes: an increase of purpurin in rhizomes (0.04%) and pseudopurpurin in all hypogeal parts (around 0.57%), and a decrease of purpurin in all parts of hypogeal apparatus. The most important change was found in rubiadin concentration, which reached its maximum in principal stolons (11.3%). No anthraquinones were found in the aerial parts of the plant.

Two validated HPLC methods for the quantification of alizarin and other anthraquinones in Rubia tinctorum cultivars

Direct and indirect HPLC-UV methods for the quantitative determination of anthraquinones in dried madder root have been developed, validated and compared. In the direct method, madder root was extracted twice with refluxing ethanol-water. This method allowed the determination of the two major native anthraquinone glycosides lucidin primeveroside and ruberythric acid. In the indirect extraction method, the anthraquinone glycosides were first converted into aglycones by endogenous enzymes and the aglycones were subsequently extracted with tetrahydrofuran-water and then analysed. In this case the anthraquinones alizarin, purpurin and nordamnacanthal may be determined. The content of nordamnacanthal is proportional to the amount of lucidin primeveroside originally present. The indirect extraction method is easier to apply. Different madder cultivars were screened for their anthraquinone content.

Analysis of anthraquinones in cell cultures of Cinchona 'Robusta' by HPLC with photodiode array and mass spectrometry detection

An HPLC-PAD-ESI/MS method has been developed for the analysis of anthraquinones in cell cultures of Cinchona 'Robusta'. Using a C18 column and gradient elution with a mobile phase system containing acetonitrile, water and trifluoroacetic acid, a satisfactory separation of both anthraquinone glycosides and aglycones in a crude dichloromethane extract could be obtained. Robustaquinone B was identified as a major anthraquinone in the extracts, and another five anthraquinones were tentatively identified from spectroscopic data. A number of minor unknown compounds were detected and were distinguished from the known anthraquinones. An isocratic system for the quantitative determination of robustaquinone B has also been developed.

Metabolite profiling of alkaloids and strictosidine synthase activity in camptothecin producing plants

Camptothecin derivatives are clinically used anti-neoplastic alkaloids that biogenetically belong to monoterpenoid indole alkaloids. Camptothecin-related alkaloids from the methanol extracts of Ophiorrhiza pumila, Camptotheca acuminata and Nothapodytes foetida plants were profiled and identified using a reverse-phase high performance liquid chromatography coupled with on-line photodiode array detection and electrospray-ionization ion-trap mass spectrometry. A natural 10-glycosyloxy camptothecin, chaboside, was accumulated in tissues of O. pumila but not in C. acuminata and N. foetida. Anthraquinones regarded as phytoalexins were present in the extracts of hairy roots and calli but not in the differentiated plants of O. pumila. These findings demonstrated a remarkable difference in the constituents between the differentiated plants and the hairy roots or calli tissues. The activity of strictosidine synthase, a key enzyme of camptothecin biosynthesis, was detected in the protein extracts of stems and roots of O. pumila, being correlated with the pattern of strictosidine synthase mRNA expression.

Biosynthesis of anthraquinones in cell cultures of Cinchona 'Robusta' proceeds via the methylerythritol 4-phosphate pathway

Robustaquinone B was found as a major anthraquinone in cell cultures of Cinchona 'Robusta' after treatment with a fungal elicitor. Anthraquinones in Cinchona are considered to be of the Rubia type, i.e. rings A and B are derived from chorismate and alpha-ketoglutarate, whereas ring C is formed from isopentenyl diphosphate (IPP). To determine the origin of IPP, either formed via the mevalonic acid pathway or the 2-C-methyl-D-erythritol 4-phosphate pathway, the incorporation of [1-13C]glucose into robustaquinone B was studied. The 13C labeling of robustaquinone B was analyzed by one- and two-dimensional NMR spectroscopy and the labeling pattern was compared with the hypothetical labeling patterns obtained via the different biosynthetic pathways. The results clearly show that the IPP, constituting the ring C of robustaquinone B, is biosynthesized via the 2-C-methyl-D-erythritol 4-phosphate pathway. Moreover, the data also confirm that rings A and B of robustaquinone B are formed from chorismate and alpha-ketoglutarate via o-succinylbenzoate.

Engineering the plant cell factory for secondary metabolite production

Plant secondary metabolism is very important for traits such as flower color, flavor of food, and resistance against pests and diseases. Moreover, it is the source of many fine chemicals such as drugs, dyes, flavors, and fragrances. It is thus of interest to be able to engineer the secondary metabolite production of the plant cell factory, e.g. to produce more of a fine chemical, to produce less of a toxic compound, or even to make new compounds, Engineering of plant secondary metabolism is feasible nowadays, but it requires knowledge of the biosynthetic pathways involved. To increase secondary metabolite production different strategies can be followed, such as overcoming rate limiting steps, reducing flux through competitive pathways, reducing catabolism and overexpression of regulatory genes. For this purpose genes of plant origin can be overexpressed, but also microbial genes have been used successfully. Overexpression of plant genes in microorganisms is another approach, which might be of interest for bioconversion of readily available precursors into valuable fine chemicals. Several examples will be given to illustrate these various approaches. The constraints of metabolic engineering of the plant cell factory will also be discussed. Our limited knowledge of secondary metabolite pathways and the genes involved is one of the main bottlenecks.

Purification and characterization of two isoforms of isopentenyl-diphosphate isomerase from elicitor-treated Cinchona robusta cells

In Cinchona robusta (Rubiaceae) cell suspension cultures, the activity of the enzyme isopentenyl-diphosphate isomerase (isopentenyl-POP isomerase) is transiently induced after addition of a homogenate of the phytopathogenic fungus Phytophthora cinnamomi. The enzyme catalyses the interconversion of isopentenyl-POP and dimethylallyl diphosphate (dimethylallyl-POP) and may be involved in the biosynthesis of anthraquinone phytoalexins that accumulate rapidly after elicitation of Cinchona cells. From elicitor-treated C. robusta cells, two isoforms of isopentenyl-POP isomerase have been purified to apparent homogeneity in four chromatographic steps. The purified forms are monomeric enzymes of 34 kDa (isoform I) and 29 kDa (isoform II), with Km values for isopentenyl-POP of 5.1 microM and 1.0 microM, respectively. Both isoforms require Mn2+ or Mg2+ as cofactor, isoform II showing a preference for Mn2+ with maximum activity at 1.5-2 mM. Isoform I was most active in the presence of 0.5-1.5 mM Mg2+ or in the presence of 0.5 mM Mn2+. A pH optimum of 7-7.8 was found for both forms and both were competitively inhibited by geranyl diphosphate (Ki 96 microM for isoform I) and the transition state analogue 2-(dimethylamino)ethyl diphosphate. Rechromatography of purified isoforms did not indicate any interconversion of both forms. Western blot analysis, using antibodies raised against isopentenyl-POP isomerase purified from Capsicum annuum, showed the presence of both isoforms in the crude protein extracts from C. robusta cells. Isoform II was specifically induced by elicitation, non-treated cells contained low activity of this isoform. The possible role of isopentenyl-POP isomerase in the biosynthesis of anthraquinones is discussed.

Biotechnology and biosynthesis of quinones

Nowadays, it is generally agreed that intensive investigation of biosynthetic pathways is a prerequisite for attaining industrial-scale production of secondary metabolites (e.g. quinones) by plant cell cultures. Literature data are presented to illustrate different aspects of today's quinone biosynthesis research.

Elicitor-induced tyrosine decarboxylase in berberine-synthesizing suspension cultures of Thalictrum rugosum

Tyrosine decarboxylase (EC 4.1.1.25) was induced in suspension cultures of Thalictrum rugosum by treatment with a yeast glucan elicitor. Maximum induction was observed at a carbohydrate concentration of 0.4 mg/g fresh weight of cells and maximum enzyme activity was reached 20 h after addition of elicitor. The enzyme was inducible in late exponential and early stationary growth phases. A good correlation between induced tyrosine decarboxylase activity and berberine biosynthesis has been established. It is suggested that tyrosine decarboxylase may be a key enzyme between primary and secondary metabolisms in the biosynthesis of norlaudanosoline-derived alkaloids.

Induction of triterpene biosynthesis by elicitors in suspension cultures of Tabernaemontana species

Treatment of suspension cultures of some Tabernaemontana species (Apocynaceae) with elicitors (e.g. cellulase, Candida albicans) result in a rapid de novo production of antimicrobial active triterpenes. The triterpenes are identified as ursene carboxylic acid derivatives. These triterpenes are not produced by an elicited cell suspension culture of Catharanthus roseus, another Apocynaceae.

Effects of nutritional and hormonal factors on growth and production of anthraquinone glucosides in cell suspension cultures of Cinchona succirubra

Cell suspension cultures of Cinchona succirubra were found to produce anthraquinone glucosides. The effects of nutritional and hormonal factors on growth and anthraquinone production were investigated in order to study the enzymecatalyzed glucosylation of these metabolites.

Anthraquinones as phytoalexins in cell and tissue cultures of Cinchona spec

The addition of autoclaved mycelia of Aspergillus niger and the known phytopathogenic fungus Phytophtora cinnamomi to cultured cells of Cinchona ledgeriana Moens. caused a marked increase in the anthraquinone content of the plant cells. This finding in combination with the antimicrobial activity of the anthraquinones isolated from calli of Cinchona pubescens Vahl. led to the conclusion that anthraquinones are phytoalexins.