Senescence and the Fluidity of Rose Petal Membranes: Relationship to Phospholipid Metabolism

In previous work, senescence of rose petal cells has been shown to be accompanied by a gradual decrease of membrane fluidity, as measured by a fluorescence polarization technique. Concomitantly, an increase in the free sterol-to-phospholipid ratio was found. Both observations were verified in this study. Further, experiments carried out on whole tissue and isolated protoplasts during senescence revealed that there was no quantitative change in the level of free sterols. The content of phospholipids decreased without any significant change in their composition. Results from experiments measuring the incorporation of [32P]orthophosphate indicated a reduced capacity for phospholipid synthesis in senescent cells. Both young and old tissue showed phospholipase A and D activity, the former increasing with age. It was concluded that the fluidity of rose petal membranes decreases with age as a result of a decrease in phospholipid content, brought about by both reduced synthesis and enhanced degradation. Evidence supporting the view that the phenomena observed are related specifically to changes in the plasmalemma is discussed.