Acyl Chain and Head Group Regulation of Phospholipid Catabolism in Senescing Carnation Flowers

Abstract

Microsomal membranes from the petals of senescing carnation (Dianthus caryophyllus L.) flowers contain phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylinositol. These phospholipid classes decline essentially in parallel during natural senescence of the flower and when microsomal membranes isolated from young flowers are aged in vitro. However, measurements of changes in the endogenous molecular species composition of microsomal phospholipids during natural senescence of the flower petals and during in vitro aging of isolated membranes have indicated that the various molecular species of phospholipids have quite different susceptibilities to catabolism. Acyl chain composition and the nature of the head group are both determinants of their susceptibility to catabolism. As well, a comparison of the phospholipid catabolism data for naturally senesced membranes and for membranes aged in vitro suggests that the phospholipid composition of membranes is continuously altered during senescence by acyl chain desaturation and possibly retailoring so as to generate molecular species that are more prone to catabolism. The results collectively indicate that provision of particular molecular species of phospholipids with increased susceptibility to degradation contributes to enhanced phospholipid catabolism in the senescing carnation petal.Loss of membrane integrity is an early and fundamental feature of senescence in plant tissues, and perhaps the clearest manifestation of this is the onset of leakiness attributable to increased membrane permeability. In petals of cut carnation flowers, for example, solute leakage is detectable before petal inrolling and the climacteric-like rise in ethylene production, symptoms that are thought to denote the initiation of petal senescence (7). Studies with various techniques including electron spin resonance (20), fluorescence depolarization (9), freeze-fracture electron microscopy (24), and x-ray diffraction ( 19) (18) and results in a substantial increase in the sterol:phospholipid ratio of membranes as senescence progress (9, 29). Several phospholipid degrading enzymes have been identified in plant tissues including phospholipase D (13), lipolytic acyl hydrolase (10), and phospholipase C ( 14), and recent evidence suggests that phospholipase D may initiate phospholipid catabolism in senescing membranes (5). Although there is clear evidence for a net decline in phospholipid levels with advancing senescence, the extent to which this reflects decreased synthesis, enhanced catabolism, or possibly both has not been resolved. An age-related reduction in phospholipid synthesizing ability has been demonstrated in a number of plant tissues (3). Increased lipid catabolism during senescence has also been observed, but under conditions in which there is no absolute increase in phospholipase activity (27). This suggests that in at least some senescing tissues enhanced degradation of phospholipid may be attributable to alterations in membrane lipids that make...

Rapid turnover of polyphosphoinositides in carnation flower petals

“…Also in the green alga Chlamydomonas, a long-chain polyunsaturated fatty acid (C22:4) seems characteristic of these lipids (Brederoo et al 1991). In carnation flowers the major fatty acid of PtdInsP were palmitic (16:0) and linoleic (18:2) acid (95 %) which are also the common fatty acids of the structural phospholipids (Brown et al 1991). This is consistent with a previous report of the composition of polyphosphoinositides in carrot cells (Van Breemen et al 1990).…”

“…These percentages are not the same as the relative masses of the phospholipids for they are 40% (PtdCho), 26% (PtdEtn), 18% (PtdGro) and 5% (PtdIns) (Brown et al 1991). This indicates that isotopic equilibrium was not reached after 24 h and that PtdIns was preferentially labelled, perhaps because it is the precursor of the very rapidly labelled polyphosphoinositides.…”

“…385:35: 1. Since PtdIns accounts for 5% of the total phospholipids (Brown et al 1991), the amounts of PtdInsP and PtdInsP2, on a molar basis, are 0.45% and 0.013%, respectively, of the total phospholipids, or 8.3% and 0.23%, respectively, of the phosphoinositides. Others have reported ratios of PtdIns: PtdInsP: PtdInsP2 ranging from 300: 17:1 to 10: 1: !…”

“…Clearly PtdInsP and PtdOH incorporated more label than the major structural lipids, and while PtdInsP2 only incorporated as much as PtdEtn, this was far in excess of its relative mass. Of the structural lipids PtdIns was the first to be labelled, while it is the least abundant (Brown et al 1991).…”

Senescence-induced expression of a homologue of ?9 desaturase in rose petals

“…However, Brown etal. [2] reported that, during senescence of carnation petals, microsomal phospholipids with polyunsaturated fatty acids were selectively degraded. Comparing the degradation of phospholipids of naturally aged membranes and membranes that had been aged in vitro, they obtained evidence that desaturases and retailoring enzymes have roles in generating polyunsaturated fatty acids that are more susceptible to catabolism that saturated fatty acids.…”