Hüser, Anke Christine (2009) Gamma-aminobutyric acid Metabolism in Arabidopsis thaliana. PhD thesis, Universität zu Köln.
The four-carbon, non-protein amino acid gamma aminobutyric acid (GABA) is found in all species, where it is involved in various signaling processes. GABA is best characterized as the main inhibitory neurotransmitter in mammalia. On the contrary, work in plants focused mainly on a metabolic role; just some recent findings indicate GABA having a possible signaling function in plants as well. In Arabidopsis thaliana, mutants of both catabolic genes (GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH)) display phenotypic deviations to wild type; the former grow vegetatively like wild type, but are less fertile due to a misguidance of pollen tubes. The latter are severely affected in growth and development, probably induced by the accumulation of GABA-shunt metabolites and/or reactive oxygen intermediates. The ssadh phenotype can be suppressed by interrupting the GABA-shunt upstream of the SSADH function. Based on this, two topics should be covered in this thesis. First, the substance causing the ssadh phenotype should be identified; hence, wild type along with GABA-shunt single and double mutants were grown on media containing GABA-shunt intermediates, and plant growth as well as metabolite content in leaf extracts was examined. Second, further genes involved in regulation or function of the GABA-shunt or in sensing of GABA-shunt related metabolites should be identified. Therefore, a population of mutagenized ssadh plants was screened for suppressors; among several stable, non-segregating lines, two new gaba-t alleles were isolated. All GABA-shunt intermediates influence plant growth and development. First, GABA enhances plant growth by inducing expression of nitrate uptake transporters, only very high cellular concentrations have an inhibitory effect on plant growth. Second, succinic semialdehyde (SSA) considerably reduces plant growth when applied with the growth media, and higher concentrations (0.8 mM and more in the media) induce dedifferentiation mainly of hypocotyl cells in a yet unknown manner. Finally, the enzymatic reduction of SSA produces gamma-hydroxybutyric acid (GHB), which leads to reduced root growth in Arabidopsis without major effects on rosette size when accumulating in plant tissues
Actions (login required)