Testing the accuracy of using peroxidase activity to indicate stigma receptivity

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Abstract
Stigma peroxidase activity was tested in flowers of Pedicularis canadensis and Clintonia borealis at discrete age-classes during the course of anthesis. For recipient flowers of each age-class pollen adhesion, rate of pollen germination, and total number of grains germinating on stigmas were scored following hand-pollination. In P. canadensis, the onset of the detectable peroxidase activity occurred at the transition from the juvenile to pollen-dehiscing ag-class. Concurrently, the stickness of the stigma surface and total number of grains germinating on the stigma increased significantly. Stigma peroxidase was present to some degree throughout anthesis in C. borealis. However, the percentage of the stigma surface in which peroxidase was detectable increased significantly between straight-sided and medium-curled flower age-classes. Again, corresponding increases occurred in the stickiness of the stigma surface and total number of grains germinating. Results suggest that for both species stigma peroxidase activity is a reliable indicator of receptivity.