Investigations of trypsin inhibitors in leaves of four North American prairie grasses.

Leaves of four important North American prairie grasses (Agropyron smithii, Andropogon gerardii, A. scoparius, and Bouteloua gracilis) were examined for the presence of trypsin inhibitors which are thought to protect some plant species from herbivory. Leaves of all four species had significant inhibitor activity at levels comparable to those in tomato leaves. Our evidence suggests that part of the inhibitor activity was proteinaceous and part may have been polyphenolic. Young leaves ofA. Smithii had more inhibitory activity than old leaves, but no leaf age differences were observed inB. gracilis. Mechanical wounding of leaves ofA. Smithii caused no consistent increase in inhibitor activity, in contrast to reports for some plant species. Plants ofA. smithii collected from areas heavily grazed by prairie dogs had trypsin inhibitor levels comparable to those in plants collected from a grazing exclosure. Thus, the ecological role of proteinase inhibitors in these Great Plains dominants remains to be demonstrated.