PARENT SESSION
Oral Session #45: Herbivory: Effects on Plants. Presiding: T. Craig.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.
Are induced defenses in plants more costly under competition? A manipulative approach.
CIPOLLINI, DON1, 1
ABSTRACT- In addition to directly reducing fitness in plants, competition is thought to increase the magnitude of fitness costs of resistance. In a greenhouse experiment, I examined the effect of salicylic acid (SA) on peroxidase (POD) activity and seed mass on individuals of five lines of Arabidopsis thaliana grown alone or in competition. SA is a hormone known to induce increases in levels of many chemical defenses, including POD. In addition to wild-types, lines included the transgenic nahG line, that degrades SA in planta, the nim1-1 mutant, that is defective in responsiveness to SA, and the cep mutant, that constitutively expresses high levels of SA. Ten plants of each line in each competition treatment were sprayed with either 0 mM, 0.5 mM, or 1.0 mM SA, three times during the experiment. Leaf samples were harvested midway through the experiment to verify the effect of SA and seeds were harvested as they matured. SA increased POD activity, while competition reduced activity. Lines varied in POD activity, and were differentially affected by SA and competition. Total seed mass varied among the lines. Competition reduced seed mass overall, but its effect varied by line. Seed mass in the nahG line was severely reduced by competition, while seed mass in the wild-type ecotype Wassilewskija was unaffected by competition. SA reduced seed mass, but its effects varied by line and the presence of competition. Seed mass was reduced by 1.0 mM SA with or without competition, but reductions in seed mass by 0.5 mM SA were only detectable in some lines with competition.
KEY WORDS: induced defense, costs of defense, competition, Arabidopsis thaliana