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New Crops

Irrigation to Maximize Vaccine Antigen Production in Genetically Modified Tobacco

^a Univ. of Missouri-Delta Research Center, P.O. Box 160, Portageville, MO 63873
^b USDA Cropping Systems and Water Quality Research Unit, Portageville, MO 63873
^c Chlorogen, Inc., 893 North Warson Road, St. Louis, MO 63141

^* Corresponding author (stevensw{at}missouri.edu)

A protective antigen (PA) gene from Bacillus anthracis Cohn has been inserted into tobacco (Nicotiana tabacum L.) chloroplasts to produce an anthrax vaccine. The PA protein is the primary immunogen of human vaccines for anthrax disease. The objective of this study was to determine the optimum soil water content for producing antigen vaccine in tobacco leaves. High leaf antigen concentration is important in vaccine manufacturing. Protective antigen tobacco, transformed from ‘Petite Havana SR1’, was transplanted to native soil (fine-loamy, mixed, thermic Typic Argiudolls) in a greenhouse floor. Treatments consisted of soil water potential () irrigation thresholds (–20, –34, –48, and –62 kPa) based on sensors buried 10 cm in soil. Since plant growth is normally stimulated when soil moisture is readily available, we hypothesized that soil moisture might dilute leaf PA content. Results showed that increasing biomass with optimum irrigation did not dilute PA in leaves. Using ELISA quantification, –34 kPa irrigation threshold averaged 529 µg PA kg^–1 leaf fresh weight for two ratoon harvests. Leaves from drier irrigation treatments did not have significantly higher PA content or biomass. Tobacco grown with more frequent irrigations using –20 kPa threshold averaged less biomass and produced leaves with significantly lower antigen. In a separate experiment, gravimetric soil water use was compared between nontransgenic Petite Havana and PA plants at button growth stage. Genetic engineering tobacco for PA caused reduced leaf area in plants. Transpiration was significantly higher with nontransgenic plants, indicating that lower irrigation rates may be needed for antigen tobacco.

Abbreviations: , soil water potential • PA, protective antigen • PAR, photosynthetically active radiation • PMP, plant-made pharmaceutical

Received for publication July 5, 2006.