Thesis (doctoral)--Universität Jena, 1911. / Includes bibliographical references (p. 57-58).

Induction of phenylpropanoid metabolism in many plants is associated with the induction of plant defence responses. Among these are the accumulation of phenylpropanoid-derived phytoalexins, increase in lignification around infected sites, and the accumulation of wall-bound phenolic compounds. I show in this work, that H11 hybrid cell suspension cultures when treated with either of three elicitors respond with an increase in phenylpropanoid metabolism. Activation proceeds rapidly from PAL and 4CL mRNA accumulation, to a massive increase in extractable PAL enzyme activity and finally there is accumulation of specific phenolic compounds in the cell extracts, culture filtrates, and cell walls. In addition, elicitor treatment causes cells to turn brown, indicative of phenolic compound accumulation. As in other plants, induction is dependent on culture age, is dose dependent, and the kinetics of induction is the same with all three elicitors. Based on the previously established mode of action of PGA lyase as an elicitor, it is concluded that in poplar, as in other plants, defence responses can be induced by elicitors from both fungal and plant cell wall origin. These results illustrate the successful use of plant suspension cultures as a simplified system to study inducible defence responses. In addition, and consistent with the ubiquitous nature of phenolics in poplar, phenylpropanoid metabolism may play an important role in plant defence responses in this species. / Science, Faculty of / Botany, Department of / Graduate

Thesis (D.Phil.)(Botany)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 115-132).

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Small RNAs are important regulators for a variety of biological processes, including leaf development, flowering-time, embryogenesis and defense responses. Most ancient miRNAs are conserved among different plant species and well characterized, while young MIRNA genes are considered to be non-conserved, highly species-specific and less well-studied. miR163 is a non-conserved miRNA and its locus has evolved recently by inverted duplication events of its target gene. Previously, we have shown that miR163 acts as a negative regulator of defense response. However, it remains unclear how miR163 and its targets are being regulated in response to pathogen attacks. Here, we further elucidated the molecular controls and the involvement of miR163 and its targets in plant defense response. Elevated level of miR163 was observed by Pst treatment in Arabidopsis thaliana, and this upregulation was found to be important in controlling the accumulation of its targets (PXMT1 and FAMT), to which they were also inducible by Pst treatment. Transcript and protein level analyses in transgenic plants overexpressing miR163-resistant form of PXMT1 or FAMT provided evidence for miR163 in fine-tuning its targets, suggesting that the stress-inducible miR163 and its targets act in concert in affecting defense genes expression. Epigenetically, histone deacetylation was found to involve in the repression of miR163 targets before and after Pst infection. Our findings revealed additional mechanistic insights to the controls and the evolutionary significance of young miRNA in mediating plant defense pathways against biotic stresses.

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.

Biotic stress is one of the most serious constraints on rice productivity. Strategy adopting regulators in signal transduction of systemic acquired resistance for conferring long-lasting disease resistance against broad spectrum of pathogens become highly favorable. To achieve this, signal transduction of disease resistance should be well characterized. / OsGPBP1 is a putative G-protein binding protein and interacts with a member of the YchF G-protein subfamily that has not been thoroughly studied in plants, while OsRHC1 is a novel RING zinc finger protein harboring multiple transmembrane domains at the N-half and a unique RING-HC domain at the C terminus. Both of them were induced in the bacterial blight resistant near isogenic rice line upon wounding. Gain-of-function tests in transgenic Arabidopsis thaliana showed that their ectopic expressions are able to trigger the expression of both defense marker genes mediated either by SA- or JA/ET-pathways and led to increased resistance toward the pathogen Pseudomonas syringae pv. tomato DC3000 and both of the two clones seemed to rely on NPR1 (disease resistance key regulator) for function. Furthermore, over-expressions of the two clones in its native system are also able to activate rice defense marker genes. / Suppression subtractive hybridization experiment, using RNA samples from a pair of near-isogenic rice lines either containing the R gene Xa14 (CBB14) or its susceptible recurrent parent (SN1033), were previously performed in our laboratory. Two gene candidates ( OsGPBP1 and OsRHC1) probably encoding two novel types of signal transduction components related to disease resistance are chosen for further analysis. / Cheung, Ming Yan. / "September 2007." / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4555. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 148-168). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

A 12-kDa ribonuclease was purified from Pleurotus sajor-caju . The ribonuclease inhibited fungi growth and two species of bacteria, Pseudomonas aeruginosa and Staphylococcus aureus. It reduced the viability of hepatoma and leukemia cells and inhibited translation in a cell-free rabbit reticulocyte lysate system. / A 13-kDa lectin was isolated from Collybia veultipes. Its N-terminal sequence shows some similarity to other fungal immunomodulatory proteins. It stimulated [3H-methyl] thymidine uptake by mouse splenocytes and inhibited proliferation of leukemia cells. / A 14.4-kDa antifungal protein was purified from Agrocybe cylindracea . It exerted antifungal activity but lacked inhibitory activity against bacteria when tested up to 300 muM. It attenuated the activity of HIV-1 reverse transcriptase. / A 17-kDa hemolysin was purified from Pleurotus eryngii. It exhibited cytotoxicity toward leukemia cells but not toward fungi. It exhibited antibacterial activity against Bacillus species. / A 27.5-kDa antifungal protein, with an N-terminal sequence similar to heat shock protein and endoglucanase, was purified from Lentinula edodes. It inhibited fungal growth and exerted an inhibitory activity on HIV-1 reverse transcriptase and proliferation of leukemia cells. / A 7-kDa ubiquitin-like protein was purified from Agrocybe cylindracea . It showed antiproliferative activity on leukemia and hepatoma cell lines, and enhanced nitric oxide production in murine peritoneal macrophages. / An 18-kDa lectin, with an N-terminal sequence similar to some lectins and fungal immunomodulatory proteins, was isolated from Ganoderma capense. It exhibited potent mitogenic activity toward mouse splenocytes, and antiproliferative activity toward leukemia and hepatoma cells. / Mushrooms produce a variety of proteins with interesting biological activities. They include lectins, antifungal proteins, ribonucleases, ubiquitin-like proteins, hemolysins and other peptides. / This study demonstrates that different types of defense proteins with diverse biological activities are produced by mushrooms. Some overlap is observed in the spectra of biological activities of the same type of defense proteins. The results of protein characterization provide crucial information for future genetic manipulation in agricultural and food industries. Studies of the in vitro action of the abovementioned defense proteins on fungi, bacteria, viral enzyme, immune cells and cancer cells indicate that the proteins are potentially exploitable drug agents. / Ngai Hung-kui. / "July 2005." / Adviser: Ng Tzi Bun. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0012. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 228-294). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

The plant hormone, abscisic acid (ABA), has previously been shown to have an impact on the resistance or susceptibility of plants to pathogens. In this thesis, it was shown that ABA had a regulatory effect on an extensive array of plant defence responses in three different plant and pathogen interaction combinations as well as following the application of an abiotic elicitor. In unique studies using ABA deficient mutants of Arabidopsis, exogenous ABA addition or ABA biosynthesis inhibitor application and simulated drought stress, ABA was shown to have a profound effect on the outcome of interactions between plants and pathogens of differing lifestyles and from different kingdoms. The systems used included a model plant and an important agricultural species: Arabidopsis thaliana (Arabidopsis) and Peronospora parasitica (a biotrophic Oomycete pathogen), Arabidopsis and Pseudomonas syringae pathovar tomato (a biotrophic bacterial pathogen) and an unrelated plant species, soybean (Glycine max) and Phytophthora sojae (a hemibiotrophic Oomycete pathogen), Generally, a higher than basal endogenous ABA concentration within plant tissues at the time of avirulent pathogen inoculation, caused an interaction shift towards what phenotypically resembled susceptibility. Conversely, a lower than basal endogenous ABA concentration in plants inoculated with a virulent pathogen caused a shift towards resistance. An extensive suppressive effect of ABA on defence responses was revealed by a range of techniques that included histochemical, biochemical and molecular approaches. A universal effect of ABA on suppression or induction of the phenylpropanoid pathway via regulation of the key entry point gene, phenylalanine ammonia-lyase (PAL), when stimulated by biotic or abiotic elicitors was shown. ABA also influenced a wide variety of other defence-related components such as: the development of a hypersensitive response (HR), the accumulation of the reactive oxyden species, hydrogen peroxide and the cell wall strengthening compounds lignin and callose, accumulation of SA and the phytoalexin, glyceollin and the transcription of the SA-dependent pathogenesis- related gene (PR-1). The near genome-wide microarray gene expression analysis of an ABA induced susceptible interaction also revealed an yet unprecedented insight into the great diversity of defence responses that were influenced by ABA that included: disease resistance like proteins, antimicrobial proteins as well as phenylpropanoid and tryptophan pathway enzymes. Subtle differences were found in the number and type of defence responses that were regulated by ABA in each type of plant and pathogen interaction that was studied. This thesis has clearly identified in plant/pathogen interactions previously unknown and important roles for ABA in the regulation of many defence responses.