M.Sc. (Biochemistry) / Plants are constantly exposed to a range of environmental stresses which can be biotic or abiotic in nature. These stresses/threats result in cross-talk between signaling pathways which trigger numerous defense responses. These reactions include activation of defense genes, accumulation of reactive oxygen species (ROS) and biosynthesis of small protective/defensive chemical compounds. The plant metabolome is comprised of primary and secondary metabolites, and while primary metabolites are involved in crucial metabolic processes such as growth and development, the latter play a key role in plant-pathogen interactions (defense). Metabolomics is one of the most recent “omic” technologies and involves the study of metabolites and their metabolic pathways under certain physiological conditions. This provides biological knowledge about the system under study giving insight into the cellular processes that define the phenotype of a cell, tissue or whole organism. In the present study a metabolomic approach was used to elucidate and analyze changes in the metabolism of Arabidopsis thaliana cells and leaves following lipopolysaccharide (LPS) treatment. Camalexin (a phytoalexin) and a group of metabolites known as glucosinolates (phytoanticipins) have been shown to accumulate in response to plant-pathogen and plant-herbivore interactions and were the main focus of the study. A number of studies involving herbivore-induced glucosinolate production have been conducted; however, in terms of microbial attack, studies are limited. The following study therefore provided insight into the effect that LPS treatment has on the biosynthetic pathways for indolic, aliphatic and aromatic glucosinolates....

M.Sc. (Biochemistry) / During microbial invasion, a variety of defense responses are induced in host plants. In order for host plants to combat potential diseases induced by microbes, they must be equipped with pattern recognition receptors (PRRs) localized at the cell surface, since such receptors enable the perception of conserved microbial epitopes termed microbe/pathogen-associated molecular patterns (M/PAMPs), thereby resulting in the activation of plant innate immunity via M/PAMP-triggered immunity (P/MTI). Lipopolysaccharide (LPS) is the major component of the outer leaflet of the external membrane of Gram-negative bacteria. This thermo-stable lipoglycan is exposed towards the external environment and plays an important role in bacterial adaptation to external surroundings. LPS is recognized as a major M/PAMP in plants, and thus potentiates or elicits defense-related responses such as the production of antimicrobial compounds and the expression of immune response genes. One of the most widely investigated effects of LPS on plants is its ability to prevent and/or suppress the hypersensitive response (HR) induced by an array of bacteria. The HR is a programmed cell death response which ends in a local necrosis of plant tissue, thereby resulting in a reduced number of viable bacteria that can further promote disease progression in the host.