Abstract
Microsomal membranes isolated from petals of senescing carnation petals are able to enzymatically degrade exogenous radiolabelled phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. A comparison of the rates of catabolism for various radiolabelled molecular species of each of these phospholipid classes suggests that microsomal phospholipids have different susceptibilities to degradation. The same degradation preferences are exhibited by young and senescent membranes, and they appear to reflect recognition by the degrading enzyme of both the head group and acyl chain composition of the phospholipid. There is no increase with advancing senescence in the capability of isolated microsomal membranes to catabolize radiolabelled phospholipids, and there is no change with age in phospholipid composition of microsomal membranes. Yet, levels of microsomal phospholipid decline with advancing senescence by ca three-fold relative to corresponding levels of membrane free sterols. The data indicate that the decline in microsomal phospholipid with advancing petal senescence cannot be attributed to increased membrane-associated phospholipase activity, and they raise the possibility that provision of particular molecular species of phospholipids with increased susceptibility to degradation could be the underlying basis for enhanced phospholipid catabolism during petal senescence.
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