SUMMARYThe pollination‐induced wave of peroxidase isoenzyme 10 activity in matureNicotiana alatastyles does not occur in immature styles unless pollinated within one day before anthesis. The capacity of a style to increase peroxidase 10 activity arises at the same time as the shift from compatibility to incompatibility. In styles selfed at 4 days after anthesis the peroxidase 10 wave is transmitted with a higher speed as compared to styles selfed at anthesis.The present results are discussed in relation to the hypothesis that peroxidase 10 is involved in the rejection of incompatible pollen tubes. It is not clear yet whether the presence of this isoenzyme is necessary to stop incompatible pollen tube growth. However, there exists a positive correlation between peroxidase 10 activity and the strength of the rejection reactio