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Urushiols are the chemical constituents responsible for causing the characteristic skin rash resulting from contact with poison ivy [Toxicodendron radicans subsp. radicans (L.) Kuntze] plant tissue. Future detailed physiological and molecular studies of T. radicans urushiol metabolism will require the production and cultivation of axenic T. radicans plants in controlled environments. To this end, the present study focused on treatments to enhance germination and reduce microbial contamination to obtain axenic T. radicans seedlings. Toxicodendron radicans drupes treated singularly with water, bleach, cold, or gibberellic acid showed very low germination frequencies. In contrast, concentrated sulfuric acid strongly promoted seedling germination by removing exocarp, mesocarp, and causing pitting of the brachysclereid and osteosclereid layers of the endocarp. Most T. radicans drupes harbored significant amounts of fungal and bacterial contaminants. Although the serial mechanical scarification, sulfuric acid, and bleach treatments promoted seedling germination, this serial treatment regime was not adequate to render the majority of drupes microbe-free. Nevertheless, ≈25% of treated T. radicans drupes were axenic, and these needed to be promptly separated from adjacent fungal-contaminated drupes to avoid cross-contamination. The isolated axenic T. radicans drupes germinated at high frequency producing viable seedlings that grew well in sterile plant culture conditions.
Poison ivy [Toxicodendron radicans (L.) Kuntz] is a widely recognized native plant species because of its production of urushiol, which is responsible for delayed contact dermatitis symptoms in humans. Poison ivy is predicted to become both more prevalent and more noxious in response to projected patterns of climate change. Future studies on poison ivy chemical ecology will require reverse genetics to investigate urushiol metabolism. A prerequisite for reverse genetic procedures is the introduction and expression of recombinant DNA into poison ivy tissues. Poison ivy leaves and cotyledons were marginally susceptible to vacuum- and syringe-agroinfiltration and expression of two firefly luciferase (LUC)–based reporter genes. The efficacy of agroinfiltration and transient LUC expression was dependent on leaf age and plant growth environmental conditions, with young leaves grown in magenta boxes showing highest transient LUC expression levels. Agroinfiltrated leaves showed an Agrobacterium-dependent accumulation of brown–colored pigments. Biolistic transformation of a LUC reporter gene did not show brown pigment accumulation and readily displayed transient LUC bioluminescence in both leaves and cotyledon tissues. These studies establish best practices for introducing and transiently expressing recombinant DNA into poison ivy leaf and cotyledon tissues, on which future reverse genetic procedures can be developed.