Assessment of Programmed Cell Death in Aging <i>Paeonia lactiflora</i> Petals

Abstract

In order to study the ultrastructural changes and characteristics associated with programmed cell death (PCD) in the petals of Paeonia lactiflora during senescence, scanning electron microscopy and transmission electron microscopy were used to observe the surface and interior of perianth slices of P. lactiflora ʻZhong Sheng Fenʼ flower petals at different blooming stages. Observations indicated that PCD in parenchyma cells occurred at an early flowering stage, even though visible petal senescence was manifested during the collapse of epidermal cells at the withering stage. The epidermal cells of the perianth were fully extended at the blooming stage and had cristae on the cell surface that were continuously distributed over the long axis of cells, while different degrees of contraction of the intercellular space was observed. The progression of PCD displayed several characteristics: vacuolar membrane rupture and organelle degradation, nuclear membrane rupture and nonuniform cell wall degradation, and cell membrane rupture and changes to the cell wall, while vacuole degradation was likely a key event marking the start of PCD. TUNEL results further confirmed the occurrence of PCD during petal senescence.