128 Musser et al. Archives of Insect Biochemistry and Physiology Archives of Insect Biochemistry and Physiology 58:128–137(2005) © 2005 Wiley-Liss, Inc. DOI: 10.1002/arch.20039 Published online in Wiley InterScience (www.interscience.wiley.com) Evidence That the Caterpillar Salivary Enzyme Glucose Oxidase Provides Herbivore Offense in Solanaceous Plants Richard O. Musser, 1 Don F. Cipollini, 2 Sue M. Hum-Musser, 1 Spencer A. Williams, 1 Judith K. Brown, 3 and Gary W. Felton 4 * The insect salivary enzyme glucose oxidase (GOX) can inhibit wound-inducible nicotine production in tobacco, Nicotiana tabacum. We examined whether salivary gland extracts of Helicoverpa zea lacking active GOX could still suppress nicotine in tobacco, Nicotiana tabacum, and whether GOX could suppress wound-inducible defenses of another Solanaceous plant, tomato Lycopersicon esculentum. Tobacco leaves were wounded with a cork borer and treated with water, salivary gland extracts with active GOX (SxG), or salivary gland extracts with inactive GOX (SxI). After three days, leaves treated with SxG had significantly less nicotine than all other wounded treatments. Neonates that fed on the terminal leaves of tobacco plants treated with SxG had significantly higher survival than neonates that fed on leaves treated with either SxI or water. This evidence supports the assertion that GOX is the salivary factor responsible for the suppression of tobacco plant nicotine production by H. zea saliva. Results for the NahG tobacco plants, which lack salicylic acid (SA) due to a transgene for bacterial SA hydroxylase, indicate that suppression of nicotine by GOX does not require SA. However, tobacco leaves that were wounded and treated with SxG had significantly higher levels of the SA-mediated PR-1a protein than leaves treated with SxI or water. Leaves of tomato plants wounded with scissors and then treated with SxG had trypsin inhibitor levels that were moderately lower than plants wounded and treated with purified GOX, water, or SxI. However, all the wounded tomato leaves irrespective of treatment resulted in lower caterpillar growth rates than the non-wounded tomato leaves. Glucose oxidase is the first insect salivary enzyme shown to suppress wound-inducible herbivore defenses of plants. Arch. Insect Biochem. Physiol. 58:128–137, 2005. © 2005 Wiley-Liss, Inc. KEYWORDS: Helicoverpa zea; reactive oxygen species; induced resistance; hydrogen peroxide; oxidative burst; elicitor; systemic acquired resistance; glucose oxidase; jasmonate; salicylate 1 Department of Biological Sciences, Western Illinois University, Macomb 2 Department of Biological Sciences, Wright State University, Dayton, Ohio 3 Department of Plant Science, Center of Insect Science, University of Arizona, Tucson 4 Department of Entomology, Pennsylvania State University, University Park Paper presented at the 51st Annual Meeting of the Entomological Society of America, October 2003. Symposium entitled Insect Saliva: An Integrative Approach. Contract grant sponsor: Illinois Department of Agriculture; Contract grant sponsor: University Research Council, Western Illinois University; Contract grant sponsor: Center for Insect Science, University of Arizona. *Correspondence to: Gary W. Felton, Department of Entomology, Pennsylvania State University, University Park, PA 16802. E-mail: gwf10@psu.edu INTRODUCTION Emerging evidence indicates that herbivore oral secretions are important mediators of inducible defenses of plants (Musser et al., 2002a,b, 2004; Alborn et al., 1997, 2000; Spiteller et al., 2000; McCloud and Baldwin, 1997; Mattiacci et al., 1995; Na and Chenzhu, 2004; Voelckel and Baldwin, 2004). Most studies on this subject have reported the identity and effects of oral secretions that act as elicitors of plant anti-herbivore defenses. These include β-glucosidase from the saliva of Pieris brassicae (Linnaeus), and the fatty acid-amino acid conjugates identified in various lepidopteran lar-