ANTIBACTERIAL ACTIVITY OF SECONDARY METABOLITES FROM IN VITRO CULTURE OF DROSERA GIGANTEA AGAINST THE PLANT PATHOGENIC BACTERIA PSEUDOMONAS SYRINGAE pv. SYRINGAE AND P. SYRINGAE pv. MORSPRUNORUM

Abstract

The carnivorous plant Drosera gigantea contains naphthoquinones among which plumbagin is known to have an antibacterial activity. The aims of this study were (i) to optimize conditions for micropropagation of D. gigantea and (ii) to evaluate the antibacterial activity of extracts of D. gigantea tissues and plumbagin against the bacterial fruit tree pathogens Pseudomonas syringae pv. syringae and P. syringae pv. morsprunorum. A number of media with different growth regulators [1-naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA), thidiazuron (TDZ) and 6-benzylaminopurine (BAP)] or activated charcoal (CA) were tested for D. gigantea micropropagation. The best medium proved to be a halfstrenght Murashige and Skoog medium (1/2 MS) with 0.4% CA. All of the tested growth regulators resulted in changed phenotype of daughter plants and RAPD analysis showed that some of the regulators caused somaclonal variation. The minimal inhibitory concentrations and the minimal bactericidal concentrations (MBCs) of methanol and chloroform extracts of D. gigantea as well as pure plumbagin were determined and were in the range of 375-1875 μg dry weight (dw)/ml for methanol extract, 240-1425 μg dw/ml for chloroform extract and 5-150 μg dw/ml for plumbagin. The lowest MBCs (750-1875 μg dw/ml) were obtained with methanol extract of D. gigantea. These results suggest that in vitro-grown D. gigantea could be a potential source of antibacterial compounds, useful for the control of bacterial fruit tree pathogens but it should be further tested under in vivo conditions.