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Title: Elicitor-induced defence response and signal mechanisms in Medicago sativa L.
Author: Tang, M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2002
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In this study, the responses and signal mechanisms were explored with a model system, concerning the interactions between lucerne suspension cells (Medicago sativa L., cv. Kabul) and elicitor either from avirulent (V2) or virulent (V1) isolate of Verticillium, alboatrum. V2 elicitor induced a two-phase of H2O2 accumulation in the cell cultures. Activation of defence expression led to an increase in PAL activity, phytoalexin accumulation and deposition of phenolic polymers. However, activities of antioxidant enzymes, such as catalase, peroxidases, glucanase, glutathione reductase, did not show obvious increase within 24 h after treatment with the elicitor. Glutathione S-transferase activity increased after 1st oxidative burst. V1 elicitor induced similar defence responses as V2 did, but a stronger response was observed when the same concentration of elicitor was used, confirming that Kabul is a resistance cultivar to V. albo-atrum. Ca2+ influx is necessary for oxidative burst, PAL activity and phytoalexin accumulation. Either blocking Ca2+ channel by La3+ or reduction of extracellular Ca2+ amount by EGTA, had an important inhibition on oxidative burst, PAL activity and phytoalexin accumulation. Intracellular Ca2+ also played a role in downstream signalling. Intracellular Ca2+ inhibitors. TBM-8 and Ruthenium red, strongly inhibited the PAL activity and phytoalexin accumulation. Oxidative burst has a relation with defence expression. An NADPH oxidase inhibitor, diphenyleneiodonium (DPI), which inhibited oxidative burst effectively, also inhibited PAL activity and phytoalexin accumulation. However, DCN, an inhibitor of peroxidase, also inhibited and oxidative burst, PAL activity and phytoalexin accumulated in micromolar range. Oxidative burst with superoxide-origin is related to defence activation. The H2O2 itself did not stimulate an activation of PAL activity. Addition of superoxide dismutase (SOD) stimulated an increase in H2O2 accumulation. Microsomal membranes are capable of superoxide synthesis when NADPH/NADH was used as electron donor, which was DPI-sensitive. This enzyme activity increased after treatment of the cell cultures with elicitor.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available