Perianth Abscission in Montbretia (Crocosmia × crocosmiiflora)

The anatomy, histochemistry, kinetics and hormonal regulation of perianth abscission in Crocosmia × crocosmiiflora (Montbretia) has been investigated. The abscission zone is anatomically well defined, with cell divisions occurring in this region at anthesis. Abscission is first detectable 3 d after perianth opening, when the walls of a group of cells beneath the adaxial epidermis show reduced staining with polyanion-specific stains, and a decline in penanth break strength also occurs. Abscission is achieved by cell wall breakage in thc abscission zone, which progresses eccentrically from the adaxial epidermis through the abscission zone, rather than the separation of intact cells as occurs in flowers of dicotyledons. Experiments on detached flowers suggest similarities in the hormonal regulation of abscission in Crocosmia to that of dicotyledons, in that an ethylene promotion, and possibly an auxin inhibition, mechanism may exist in Crocosmia. Ovary expansion occurs throughout the development and senescence of unpollinated flowers, but does not appear to be the sole cause of wall breakage in the abscission zone. It is suggested that hormonally regulated wall hydrolases weaken the cell walls in the abscission zone, and allow wall breakage and subsequent abscission to occur.