The Importance of the Stigma in Flower Senescence in Petunia (Petunia hybrida)

Abstract

Senescence of flowers of Petunia hybrida Vilm. cv Gypsy is characterized by colour changes, wilting and abscission. In emasculated detached flowers the onset of these processes is hastened by any treatment which reduces the vigour of the stigma. Thus pricking it, excising segments, or freezing with liquid nitrogen all reduce the time to morphological changes associated with corolla senescence. Removal of the stigma has the most dramatic effect, reducing lifespan of the flower by about 50 per cent, to 3 d. This reduction can be lessened if IAA or 2,4-D is applied to the cut surface of the style. In intact flowers, the style may usually be implicated in the production of a stimulus leading to corolla abscission, but abscission will also occur in the absence of the style. Some senescence acceleration takes place not only in the complete absence of the style, but also when the upper part of the ovary has been excised in addition. The speeding up of senescence and of corolla abscission cannot be due solely to damage per se since when the corolla limb was excised, leaving only the corolla tube, the tube abscised at about the same time as the controls, despite the quite extensive wounding. This also implies that the distal parts of the corolla do not play a major role in the development of the abscission zone at the base of the corolla tube. A healthy, undamaged stigma appears to be very important in corolla longevity and one of its roles may be to prevent the production of an abscission/wilting stimulus by some other component of the flower. Possibly auxins in the stigma are important in that either they are mobile and protect the abscission zone or they create a sink for other substances which are implicated in flower senescence.