Phytochemical analysis of both HEA1 and the crude plant extract showed the presence of phenolics, tannins and saponins. Saponins were the predominant secondary metabolites and were mostly abundant in the plant extract and to a lesser extent in the active compound. Steroidal saponins, tannins and phenolics were also detected in the plant extract, but only the phenolics were detected in the active compound. The results of the phytochemical analysis showed that those compounds that were not present in the active compound could be removed from the crude extract during the TLC purification process. Investigation on the mechanism of action of the crude plant extract on the sterol production by A. flavus showed that the plant extract affected ergosterol biosynthesis by causing an accumulation of oxidosqualene in the ergosterol biosynthetic pathway resulting in a decline in ergosterol production. An oscillatory response in lanosterol production was observed in the presence of the plant extract, which may be an adaptation mechanism of A. flavus to unfavourable conditions and compensation for the loss of enzyme activity which may have occurred as a result of the accumulation of oxidosqualene. The antifungal activity of the plant extract on ergosterol production by A. flavus may also be due to saponins which target the cell membrane and ergosterol production in fungi. The effect of the plant extract on the fungal cell wall of A. flavus also showed that the plant extract caused a decline in β-(1, 3) glucan production by inhibiting β-glucan synthase. The plant extract also affected the chitin synthesis pathway of A. flavus, by causing a decline in chitin production, which was due to the inhibition of chitin synthase. Investigation of chitinase production using 4MU substrates showed that the plant extract caused an accumulation of chitobioses, by activating chitobiosidases and endochitinases. A decline in N-acetylglucosaminidase activity in the presence of the plant extract was observed and this prevented the formation of N-acetylglucosamine. The accumulation of chitobiosidase and endochitinase may be as a result of autolysis that may be triggered by A. flavus as a survival mechanism in the presence of the plant extract and as a compensatory mechanism for the loss of β-glucans and chitin. The antifungal effect of the plant extract on various components of the cell wall of A. flavus, makes T. violacea aqueous plant extract an ideal chemotherapeutic agent against both human and plant pathogens of Aspergillus. The broad spectrum of antifungal activity of T. violacea against A. flavus also eliminates any chances of the fungus developing resistance towards it and would make it a candidate for use as a potential antifungal agent. Further identification and possible chemical synthesis is needed to shed light on the safety and efficacy of the active compound for further development as a chemotherapeutic agent.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nmmu/vital:21001 |
| Date | January 2015 |
| Creators | Belewa, Xoliswa Vuyokazi |
| Publisher | Nelson Mandela Metropolitan University, Faculty of Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Doctoral, PhD |
| Format | xvi, 175 leaves, pdf |
| Rights | Nelson Mandela Metropolitan University |
Page generated in 0.0016 seconds