Year of Publication

2013

Season of Publication

Spring

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Biology (MS)

Department

Biology

NACO controlled Corporate Body

University of North Florida. Department of Biology

First Advisor

Dr. Cliff Ross

Second Advisor

Dr. David Waddell

Third Advisor

Dr. Judith Ochrietor

Department Chair

Dr. Daniel C. Moon

College Dean

Dr. Barbara A. Hetrick

Abstract

Lipopolysaccharide (LPS) was shown to serve as a strong elicitor of the early defense response in the subtropical seagrass Thalassia testudinum Banks ex König and was capable of inducing an oxidative burst identified at the single cell level. The formation of reactive oxygen species (ROS) included a diphenylene iodonium sensitive response, suggesting the involvement of an NADPH oxidase. A 900 bp fragment of this enzyme was sequenced and found to encode a NAD binding pocket domain with extensive homology to the Arabidopsis thaliana rbohF (respiratory burst oxidase homolog) gene. Pharmacological dissection of the early events preceding ROS emission revealed that seagrasses contain ROS-generating machinery and signal transduction components that appear to be evolutionarily conserved with the defense response systems of terrestrial plants. It is undetermined whether or not the increased ROS associated with the oxidative burst is simply an antimicrobial agent or a signaling molecule that will initiate programmed cell death (PCD) and lead to the hypersensitive response (HR), a process not yet characterized in seagrasses. ROS accumulation was found to increase around the lesion as the duration of infection increased. The only PCD characteristic observed following infection was a slight increase in caspase-like protease activity around the lesion. Immunohistochemistry revealed inconsistent activity of proteases. Detection of nuclear condensation by TUNEL and Hoechst staining were also inconclusive and showed diffuse genetic material throughout the cytoplasm. It appears as though lesions from Labyrinthula spp. infection are likely to be a direct result of pathogen-based damage as opposed to host PCD.

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