Knoblauch im Pflanzenschutz - Wirkung, Anwendungsmöglichkeiten und molekularbiologische Studien : unter besonderer Berücksichtigung des Inhaltsstoffes Allicin

  • Garlic in plant protection : effect, possible use and molecular biological studies with special regard to the active ingredient allicin

Portz, Daniela; Slusarenko, Alan (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2008)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2008


The antimicrobial properties of garlic (Allium sativum), mainly due to the diallylthiosulfinate "Allicin", have been known for centuries. Allicin is produced when garlic tissues are damaged and the substrate alliin (S-allyl-L-cysteine sulphoxide) mixes with the enzyme alliinase (EC Allicin is readily membrane permeable and undergoes thiol-disulphide exchange reactions with free thiol groups in proteins. It has been suggested that these properties are the basis of its antimicrobial action. The objective of the present work was to contribute to the development of a garlic-based fungicide, including mode of action studies. Therefore, the effectiveness of allicin in garlic juice as a means of controlling plant disease was tested in model pathosystems including tomato / Phytophthora infestans, tomato / Alternaria solani and seed borne diseases such as carrot / Alternaria spp.. Successful protocols, often comparable with the effectivity of commercial treatments, were developed and preliminary experiments with formulations to enhance the long lasting activity were carried out. Initial field trials to assess the performance of allicin in garlic juice at controlling potato leaf blight were also carried out. Investigations of the mode of action of allicin in garlic juice showed a clear reduction in germination and germ-tube growth of sporangia and cysts of Phytophthora infestans. Using Saccharomyces cerevisiae as a model organism it was demonstrated that allicin in garlic juice pushes the cells into an oxidized state where they entered into apoptosis. These results were confirmed at the cellular level using an apoptosis-specific fluorescent probe and confocal laser scanning microscopy to detect active caspases. An additional objective of the present work was to clarify basic requirements mandatory for a genetic engineering approach. Therefore an alliinase cDNA was cloned from garlic by RT-PCR and expressed in yeast and in Arabidopsis thaliana. Although alliinase protein could be detected in yeast by Western blotting it was enzymatically inactive. However, activity was detected in Arabidopsis transformants as a first report of the expression of active alliinase in a transgenic plant species. Investigations, concerning the localization of the enzyme, including studies with different potential signal sequences of garlic alliinase, did not result in a final conclusion. The results show that it appears to be worthwhile to further develop a strategy for using garlic or allicin as a plant protection agent especially for use under glasshouse conditions or in hobby gardening. However, further research work will be necessary to develope a garlic / allicin based plant protection concept including a cost / benefit analysis. In addition there is the possibility of employing a biotechnological approach incorporating the alliinase gene into target plants to assess if resistance to pathogens can be increased under appropriate circumstances.