Exhibits specific pollen self-inhibitory activity thus preventing self-fertilization. Accumulates in the stigma (at protein level). First expressed in stigmas at low levels in flowers two days preanthesis. Accumulates rapidely the day before anthesis and stays at high levels in stigmatic tissues for several days after flower opening. Glycosylated (S1b) and unglocosylated (S1a) forms coexist. Belongs to the plant self-incompatibility (S1) protein family.