Document: DON-3-42-7

Environmental, developmental, and genetic constraints on the induction of trypsin inhibitor activity in Brassica species.

CIPOLLINI, D.* ¹ and J.BERGELSON ²

Wright State University, Dayton, OH 45435 USA ¹
University of Chicago, Chicago, Il 60637 USA ²

Abstract:
Induced chemical defenses are thought to be important determinants of plant resistance to natural enemies in the field and to represent a form of adaptive phenotypic plasticity. However, many factors can constrain the induction of defense, placing limits on the benefits of inducibility and preventing perfect phenotype-environment matching. We investigated the effect of several environmental, developmental, and genetic factors on the wound-inducibility of trypsin inhibitor activity in three Brassica species. In Brassica napus, we found that plant genotype, age, and wound location significantly influenced inhibitor induction by mechanical wounding. Increased plant density and reduced nutrient availability were found to be important environmental constraints on wound-induction, and it appears that induction is constrained by these factors independently of their effects on growth or total protein synthesis. In turn, competition with weeds significantly increased herbivory on B. napus plants in the field. Using a crossing design, we found some evidence of variation in inhibitor levels induced by caterpillar feeding among families of Brassica rapa from a wild population, and found large temporal block effects on inhibitor production. Finally, maternal half-sib families of Brassica kaber collected from a wild population exhibited some evidence of variation in wound-inducibility of inhibitors and inhibitor levels were affected by nutrient availability. Overall, these results indicate that the wound-inducibility of trypsin inhibitors in Brassica species may have a genetic basis, and that the degree of inducibility is sensitive to environmental conditions. Such factors can significantly influence the degree of matching between a defensive phenotype and a selective environment.

Keywords: adaptive phenotypic plasticity, Brassica, constraints, induced defense, trypsin inhibitors

This abstract is being presented at: 3:45 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.