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The objective of the present study was to evaluate the antioxidant as well as the antibacterial properties of secondary metabolites obtained from Drosera aliciae (Alice sundew) plants grown in vitro and to examine the mechanism of their antimicrobial action. Bactericidal activity of extracts from D. aliciae, as well as pure ramentaceone (naphthoquinone), which is present in this plant, were examined against human pathogenic strains of micro-organisms that are both resistant and susceptible to antibiotics. A chloroform extract proved to be more effective than a methanol preparation against all of the tested strains, except for Pseudomonas aeruginosa isolates. The lowest minimal-bactericidal-concentration value was in the case of Staphylococcus aureus (25-50 mg fresh weight·ml(-1)). The influence of D. aliciae extracts and ramentaceone on the synthesis of DNA, RNA or proteins in cultures of Enterococcus faecalis was estimated by measurement of the incorporation of the radioactively labelled precursors [3H]thymidine, [3H]uridine or [3H]leucine respectively. The methanol extract of D. aliciae, except for a moderate effect on DNA synthesis, had no influence on RNA and protein synthesis. The chloroform preparation caused about a 75% decrease in [3H]uridine incorporation in comparison with the control after 60 min and a significant diminution in DNA and protein synthesis (44 and 30% respectively). Ramentaceone also decreased DNA and RNA synthesis, but less efficiently than did the chloroform extract, and it caused no changes in [3H]leucine incorporation. The methanol extract from D. aliciae proved to be an effective antioxidant in both the DPPH (2,2-diphenyl-10-picrylhydrazyl free radical) and the FRAP (ferric reducing antioxidant power) assay, with the activities exceeding those of well-known antioxidants, namely the flavonoids. The chloroform extract and ramentaceone showed no antioxidative properties.

Plants belonging to genus Drosera (family Droseraceae) contain pharmacologically active naphthoquinones such as ramentaceone and plumbagin. Hairy root cultures obtained following Agrobacterium rhizogenesmediated transformation have been reported to produce elevated levels of secondary compounds as well as exhibit desirable rapid biomass accumulation in comparison to untransformed plants. The aim of this study was to establish hairy root or teratoma cultures of Drosera capensis var. alba and to increase the level of ramentaceone in transformed tissue by application of abiotic and biotic elicitors. The appearance of transformed tissues-teratomas but not hairy roots was observed 18 weeks after transformation. The transformation efficiency was 10% and all teratoma cultures displayed about 3 times higher growth rate than non-transformed cultures of D. capesis. The transformation was confirmed by PCR and Southern hybridization using primers based on the A. rhizogenes rolB and rolC gene sequences. HPLC analysis of ramentaceone content indicated 60% higher level of this metabolite in teratoma tissue in comparison to non-transformed cultures. Among the elicitors tested jasmonic acid (2.5 mg l -1 ) turned out to be the most effective. The productivity of ramentaceone in elicited teratoma cultures was about sevenfold higher than in liquid cultures of D. capensis var. alba and amounted to 2.264 and 0.321 mg respectively during 4 weeks of cultivation. This is the first report on the transformation of Drosera plant with A. rhizogenes.

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Pectobacterium atrosepticum (Pba) is a plant pathogen that causes major crop losses. Dionaea muscipula extracts and their antibacterial constituent, plumbagin, inhibit Pba growth in vitro. However, this effect is reduced when the extracts are added to bacterial cultures present on potato tubers or suspended in potato tuber filtrate (PF). To explain this, we examined the response mechanism of Pba cells to Dionaea extract and plumbagin and compared it with the effect of a bactericidal peptide -CAMEL. The addition of the extract and plumbagin to a Pba1043 culture in stationary phase increased the extracellular pectate lyase (Pel) activity in the presence of PF. While the addition of the Dionaea extract and plumbagin caused a dramatic reduction in RNA and protein synthesis in Pba1043, it did not result in cellular damage. PF alone increased the expression of Pba genes encoding protein components of cellular efflux pump systems: ompX, acrA and emrA. Application of both PF and plumbagin resulted in a synergistic stimulation of acrA gene expression. Plumbagin added to potato tubers inoculated with a field isolate Pba5A/1/2005 increased extracellular Pel activity and reduced tissue maceration but did not affect bacterial counts per gram of tissue. These results show that plumbagin in the presence of compounds from potato tuber stimulates Pel production/secretion in Pba cells and increases the expression of the acrA gene. This may be the molecular basis for the less pronounced effects of Dionaea extract on Pba in planta relative to those observed in vitro.