Research topics


In individual research projects different topics of flavonoid research in plant tissues are under investigation. The main topics are described in brief below.

Combining various approaches, e.g. chemistry, biochemistry, molecular genetics, molecular biology, genomics, and pharmacology, and different plants (model or crop species) is useful to establish the genetic bases of flavonoid diversity and accumulation in plants, to better understand the effects of food processing and the molecular bases of their bioavailability, and finally, to identify specific flavonoids with relevant impact on human health.

Aims of these projects are on the one hand the support of individual breeding programmes concerning e.g. new flower colour, pathogen defense, bioactive compounds in plant and plant extracts. On the other hand these projects focus on the characterization of bioactive flavonoid composition in plants and plant extracts for pharmaceutical and medicinal applications. 

 
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Flavonoid biosynthesis in different members of Asteraceae family

A. Gerbera Hybrids

B. others

 
» Flavonoid biosynthese in different members of Apiaceae family
   
» "Genetic engineering" - modification of the flavonoid pathway and by this the flavonoid composition in different plant tissues and suitable genotypes
   
» Safety assessment of non-nutritive flavonoids (supported by DFG)
   
» Flavonoids and cancer
 

 

 

Flavonoid biosynthesis in different members of Asteraceae family

A. Gerbera Hybrids

Gerbera Hybrids are one of the most selling cut flower worldwide. Beside productivity, desease resistance and vase long life, flower colour is one of the most import breeding aim. Two pigment groups are responsible for flower colouration in Gerbera : Carotenoids and flavonoids.

Based on chemicogenetic investigations the genetic control of flavone synthase II (FNS II) was demonstrated for the first time (Martens & Forkmann, 1998). Using differential display RT-PCR and total RNA isolated from tissue of wildtype and mutant lines a cDNA coding for a functional FNS II was isolated and expressed in yeast (Martens & Forkmann, 1999).

The Gerbera DFR clone isolated previously by Helariutta et al. (1993) was used to establish a heterologous expression systems to obtain the functional enzyme for further biochemical characterisation. Both, yeast cells and tobacco protoplasts gave an active enzyme in the soluble fraction after cells disruption. Yeast expression system was further applied to other cDNA sequences from various plant species (Martens et al., 2002).

Cooperation partner :

Prof. Dr. Teemu Teeri, Helsinki, Finland (visit).

Peter Ambrosius, nursery, Gerbera cultivation and breeding, Marbach/Neckar, Germany.

Terra Nigra b.v., Kudelstaart, The Netherlands (visit)

B. others

Various members of Asteraceen family are known to produce different flavonoids and additionally they are well known as ornamentals and in herbal medicine (e.g. Osteospermum Hybrids; Dendranthema grandiflorum; Arnika montana).

 

Flavonoid biosynthese in different members of Apiaceae family

Members of Apiaceen family, especially Petroselinum crispum (parsley), served as model plant in early flavonoid research. Several enzymes (CHS, CHI, FNS I, FHT and FLS) were reported initially from irratiated parsley cells and cell free extracts of immature leaves. FNS I, FHT and FLS were classified as FeII/2-oxoglutarate-dependent dioxygenases (2-ODD). Various other members of Apiaceen family are known to produce flavonoids and additionally they are well known in herbal medicine (e.g. Pimpinella anisum, Carum carvi, Foeniculum vulgare).

One milestone within this project was the cloning of a cDNA sequence from leaflets of parsley ('Gigante d'Italia'), coding for functional FNS I, an enzyme appearing to be confined to species of the Apiaceae (Martens et al., 2001).

cDNAs encoding FNS I, FHT and FLS proteins were amplified by RT-PCR strategie using degenerated primer derived from conserved regions of available flavonoid 2-ODD sequences. Subsequently, all three clones were functional expressed in yeast cells and verified in in-vitro assays with radiolabelled flavonoid substrates (Martens et., 2003). Now FNS I has become available in quantity for mechanistic studies as well as for the convenient preparative synthesis of radiolabelled flavones which enable further biosynthetic and biotechnological studies. In addition, the recombinant enzyme may be of value for further improvement of purification protocols (Lukacin et al., 2001), raising antibodies and the production of flavone-nutraceuticals.

Furthermore, 2-ODDs has attracted considerable attention in recent years due to their diverse reactions, such as the hydroxylation, desaturation, epoxidation or cyclization of substrates, as well as by the medicinal and biotechnology impact of some of these enzymes (e.g. isopenicillin and collagen synthases). The activities depend on ferrous iron, 2-oxoglutarate, ascorbate and molecular oxygen. Much effort has been dedicated to the identification of substrate and cofactor binding sites, active sites and elucidation of the complex reaction mechanism.

Cooperation partner :

Dr. Christopher Schofield, Oxford, U.K. (visit).

 

Flavonoid biosynthese in plant tissues

additional publications :

 

Safety assessment of non-nutritive food ingredients with focus on flavonoids (supported by DFG)

The major aim of the project is to assess the safety of flavonoids occuring ubiquitously in food plants. For this purpose, in the first step the cytotoxicity of flavonoids will be determined in a human intestinal epithelial cell culture. Moreover, interactions between flavonoids and transporters for xenobiotics will provide insights into mechanisms that control the bioavailability of flavonoids and that allow relevant drug-food interactions to be identified. The following specific subjects will be investigated:

  • Cytotoxic effects of selected flavonoids as a function of compound concentration in Caco-2 human intestinal epithelial cells.
  • Effects of selected flavonoids on MDR and MRP transport activities in Caco-2 cells.
  • The role of MDR and/or MRP in transepithelial fluxes of selected flavonoids in Caco-2 cells.

The availability of non-labelled and, additionally, of 14C-labelled flavonoids is an important prerequiste for this project. To achive this, optimized expression systems for various cDNA sequences coding for different flavonoid genes and subsequent purification protocols were used.

(see also project summary)

Cooperation partner :

Dr. Uwe Wenzel, Molecular Nutrition Unit, Technical University of Munich, Center of Life and Food Science Weihenstephan, Germany (visit).

 

"Genetic engineering" - direct modification of the flavonoid pathway and by this the flavonoid composition in different plant tissues and suitable genotypes

The diverse functions of flavonoid compounds in plants and in humans offers many potential and attractive targets for metabolic engineering approaches. Structural and also several regulatory genes have been cloned, characterized and were by now available for their use in gene transformation experiments to modify flavonoid synthesis in specific plant tissues (Forkmann & Martens, 2001).

One of the most important function of flavonoids is their contribution to the colouration of flowers and other tissues.

Based on biochemical results from respective pre-studies specific metabolic engineering strategies for the flavonoid pathway in different ornamental plants were developed (e.g. Zantedeschia, Torenia, Lilium, Pelargonium, Osteospermum) (Martens et al. 2003).

Nowadays plants are being "programmed" with recombinant DNA techniques to produce high-value-added nutraceuticals and pharmaceuticals, a process dubbed 'biopharming'. After harvesting the transgenic plants the desired compounds (drugs) were extracted and purified. Also the generation of modified crop plants as "functional foods" is increasing.

Cooperation partner :

Dr. Ric de Vos, Wageningen, The Netherlands (visit).

Related publications :

Zuker et al. 2002.

 

Flavonoids and cancer - preclinical drug development

Historically, plants were a traditional source of medicinal agents, and as modern medicine developed, numerous useful drugs were developed from lead compounds dicovered from medicinal plants. Today, this strategy remains an essential route to new pharmaceuticals.

Plants are the source of an almost uncountable number of metabolites whose structure, function and usability have been explored only partially. More than 100.000 plant secondary metabolites have already been identified, which probably represent only 10% of the actual total in nature.

Within in the large group of natural compounds flavonoids shows several bioactivities. Some compounds possess potent antitumor activity.

In this project we focus on the preclinical development of bioactive natural compounds derived mainly from the flavonoid class as chemotherapeutic agent.

Cooperation partner : Prof. Dr. Klaus Pantel, Hamburg, Germany (visit)