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Nitrogen Fertility Effects on Bt -Endotoxin and Nitrogen Concentrations of Maize during Early Growth

^a USDA-ARS, Crop Genet. and Prod. Res. Unit, Box 345, Stoneville, MS 38776
^b USDA-ARS, Southern Insect Manage. Res. Unit, Box 346, Stoneville, MS 38776

* Corresponding author (abruns{at}ars.usda.gov)

Received for publication March 4, 2002. Nitrogen deficiencies interfere with protein synthesis and growth in general in maize (Zea mays L.). Transgenic maize hybrids with the Bacillus thuringiensis Berliner (Bt) gene produce proteins that are solubilized and become insecticidal in the highly alkaline midgut of certain lepidopteran insects. The effect N fertility has on Bt -endotoxin and how whole-plant N concentrations relate to Bt -endotoxin levels has yet to be documented in early-growth maize. Two Bt maize hybrids (‘Pioneer 33V08’¹ with Bt event MON-810 and ‘Dekalb 626Bty’¹ with Bt event DBT 418) were grown in pots in duplicate greenhouse experiments with N fertility rates of 0, 112, 224, and 336 kg ha^-1 N as NH₄NO₃. Fertilizer was blended into a potting mixture of a 2:1:1 ratio of peat moss/sand/soil at planting. Plants were harvested at growth stage V5 and assayed for Bt -endotoxin using a commercial quantification plate kit. Whole-plant N concentrations were determined by semimicro-Kjeldahl. Whole-plant N concentrations were 25.8, 33.1, 35.1, and 37.7 mg g^-1, and Bt -endotoxin concentrations were 350, 367, 486, and 534 µg kg^-1 at N fertility levels of 0, 112, 224, and 336 kg ha^-1, respectively. Increased available N likely increases Bt -endotoxin–synthesizing proteins and thus increases the Bt -endotoxin concentration. The response of the two Bt hybrids to increased N fertility was similar. Adequate levels of N fertility during early growth appear essential for Bt -endotoxin production by the plant and may affect the ability of maize plants to resist insect predation.

Abbreviations: Bt, Bacillus thuringiensis • PEPC, phosphoenolpyruvate carboxylase

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