Evidence for early changes in membrane structure during post‐harvest development of cut carnation (Dianthus caryophyllus L.) flowers

SUMMARY Freeze‐fracture electron microscopy and X‐ray diffraction have indicated that there are marked alterations in membrane structure prior to the initiation of increased ethylene production and petal inrolling during post‐harvest development of cut carnation flowers. In replicas of petals from partially open flowers (stage 1 of post harvest development), an even distribution of intramembranous particles, which is characteristic of normal membranes, was evident on the fracture plane of the plasma membrane. By contrast, endoplasmic reticulum membranes had begun to develop intramembranous particle‐free areas indicative of gel phase lipid domains. By stage 2 of development, when the flowers were fully open, large areas devoid of intramembranous particles were apparent on the plasma membrane as well. The presence of gel phase lipid was confirmed by wide‐angle X‐ray diffraction of isolated microsomes. Imaginations reflecting microvesiculation were also discernible in the fracture planes of plasma membrane at stage 2 of development and vesicles lying adjacent to the cell surface were evident in the cytoplasm. These observations collectively indicate that there are deteriorative alterations in membrane structure during the very early stages of post‐harvest development in cut carnation flowers. They also provide an explanation for the previous finding that carnation petals become leaky well before morphological symptoms of senescence such as petal inrolling are apparent.