Date of Award

8-1997

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Dr. Alexander Enyedi

Second Advisor

Dr. Elwood Ehrle

Third Advisor

Dr. Stephen Malcolm

Fourth Advisor

Dr. Sue Stapleton

Access Setting

Masters Thesis-Open Access

Abstract

Previous studies have implicated the involvement of free radicals, specifically reactive oxygen species (ROS), as a key component in plant response to pathogen attack. In this study we examined the effect free radical scavenging compounds have on lesion area, salicylic acid levels, catalase, and superoxide dismutase in response to inoculation with Tobacco Mosaic Virus (TMV), a viral pathogen. Hydroponically grown Nicotiana tabacum (Xanthi nc) were pretreated with one of two antioxidants, either purpurogallin (PPG) or N-acetyl cysteine (NAC). Antioxidants were supplied to the plant via the root system and the leaves were subsequently challenged by inoculation with theTMV. Leaf material was harvested at 0, 48, and 96 hrs postinoculation. In response lo inoculation with TMV , plants pretreated with PPG did not exhibit a significant difference in necrotic lesion area, free and total salicylic acid (SA) content, and catalase and superoxide dismutase (SOD) activity over time. TMV inoculated plants pretreated with NAC exhibited a 33.4% reduction in necrotic lesion area at 48 hrs postinoculation and a 54.3% reduction in necrotic lesion area at 96 hrs postinoculation. However, there was no difference in the free and total SA and catalase and SOD activity in plants pretreated with NAC and challenged with TMV. In response to TMV inoculation, there was no difference in catalase or SOD activity. The results of this study suggest NAC significantly reduces necrotic lesion area in response to TMV-inoculation. It appears that supplying antioxidants via the roots has a limited effect on the resistance response.

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