Ultrastructural Changes in the Petals of Senescing flowers of Dianthus caryophyllus L.

Ultrastructural changes associated with carnation petal senescencewere investigated using ethylene levels of individual petalsas a physiological monitor of the senescence process. Limitedvacuolar and cytoplasmic vesiculation was observed in pre-senescentpetals which became more extensive in pre-climacteric tissues,along with dilation of the outer mitochondrial membrane. Climactericmesophyll tissue was characterized by widespread cytolysis.Intact cells possessed a highly reduced cytoplasm and vacuoleswith electron-dense deposits. Degenerative changes became evidentin the vasculature at this stage. These included occlusion ofthe sieve plate, and membrane abnormalities in the companioncells. Post-climacteric tissue was characterized by looseningof wall fibrillar structure in the vasculature, the appearanceof intracellular cytoplasmic debns and cells completely devoidof contents. These changes are discussed in relation to developmentalregulation on the one hand, and increasing levels of membranedisorgamsation on the other, leading to a possible ‘errorcatastrophe’ and final senescence. Dianthus caryophyllus L. cv., White Sim, carnation, Petal senescence, ultrastructure, ethylene, climacteric vacuoles, membranes, wall lysis