Plant allocation to defensive compounds of transgenic Bt cotton in response to infestation by cotton bollworm under conditions of elevated CO₂

Abstract

Allocation of defensive compounds of transgenic Bt cotton grown under conditions of elevated CO₂ in response to infestation by cotton bollworm, Helicoverpa armigera (Hübner) was studied in two successive years (2004 and 2005). Both CO₂ levels and bollworm infestation affected allocation of defensive compounds of non-transgenic cotton and transgenic Bt cotton. Both significantly higher foliar condensed tannin and a higher carbon/nitrogen ratio for non-transgenic cotton and transgenic Bt cotton were recorded under elevated CO₂ compared to ambient CO₂. This result accords with the Carbon Nutrient Balance hypothesis linking limiting nitrogen and excess carbon in cotton plants in response to elevated CO₂. Furthermore, significantly higher levels of catalase (CAT) and superoxide dismutase (SOD) and a significantly lower level of true choline esterase (TChE) were also observed in H. armigera fed on transgenic Bt cotton compared with those fed on non-transgenic cotton. Also, there were significant interactions between cotton variety and bollworm infestation time on CAT and SOD activities. Our results indicate that plant allocation to defensive compounds will be affected sufficiently to affect plant–herbivore populations interactions.

Keywords:

• elevated CO₂
• transgenic Bt cotton
• cotton bollworm
• defensive compounds
• plant allocation

Acknowledgments

We thank Professor Marvin Harris from Texas A&M University and PhD Norman from Ohio State University for reviewing the manuscript draft; Mrs Ding Yu Lei, the dean of Beiai Science and Technology Center of Hebei Province for much help in field OTC experiments. This project was supported by ‘National Basic Research Program of China’ 973 Program (No. 2006CB102002), the Innovation Program of Chinese Academy of Science (KSCX2-YW-N-006), the Open-Application Foundation from the State Key Laboratory of Integrated management of Pest Insects and Rodents (Chinese-IPM-0803), the National Nature Science Fund of China (No. 30800724, 30621003) and the ‘Major Projects of Cultivated Varieties of Genetically Modified Organism’ (No. 2008ZX08012-005B).