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Regulation of membrane phospholipid catabolism in senescing carnation flowers

1987; Wiley; Volume: 71; Issue: 4 Linguagem: Inglês

10.1111/j.1399-3054.1987.tb02891.x

1399-3054

Gopinadhan Paliyath, Daniel V. Lynch, John E. Thompson,

Plant biochemistry and biosynthesis

Evidence has been obtained for the involvement of μ M levels of Ca 2+ in phospholipid catabolism during petal senescence by following the breakdown of [U‐ 14 C]‐phosphatidylcholine by microsomal membranes from cut carnation ( Dianthus caryophyllus L. cv. White‐sim) flowers. Phospholipid degradation was mediated by three membrane‐associated lipases, viz. phospholipase D (EC 3.1.4.4), phosphatidic acid phosphatase (EC 3.1.3.4) and lipolytic acyl hydrolase. The activities of phospholipase D and phosphatidic acid phosphatase were stimulated by 30 and 100%, respectively, in the presence of 40 μ M free Ca 2+ , and the Ca 2+ ‐stimulation of phosphatidic acid phosphatase was calmodulin‐dependent. When L‐3‐phosphatidyl‐[2‐ 3 H]‐inositol and L‐3‐phosphatidyl‐[N‐methyl‐ 3 H]‐choline were used as substrates, inositol and choline accounted for 95 and 99%, respectively, of the water‐soluble radiolabelled products. This suggests a predominance of phospholipase D activity over phospholipase C activity in these membranes. Breakdown of membrane phospholipids in senescing carnations is known to be accelerated by treatment of young flowers with ethylene. To determine whether this involves a specific turnover of phosphatidylinositol as observed in animal systems in response to certain agonists, young flowers pre‐labelled with 32 PO 3‐ 4 were treated with 10 ppm ethylene. All phospholipids incorporated the label, but no enhanced turnover of phosphatidylinositol was observed. Inositol 1,4,5‐triphosphate did not release Ca 2+ from preloaded microsomal vesicles at concentrations known to be effective in animal systems (i.e. < 5 μ M ) although release of Ca 2+ was observed when a higher (20 μ M ) concentration was used.