MODIFICATION OF PHOSPHOLIPID CATABOLISM IN MICROSOMAL-MEMBRANES OF GAMMA-IRRADIATED CAULIFLOWER (BRASSICA-OLERACEA L)

Acceleration of membrane deterioration has been observed recently duri ng storage of gamma-irradiated cauliflower (Brassica oleracea L., Botr ytis group). In the present study, the activity of microsome-associate d lipolytic enzymes was investigated in cauliflower florets exposed to 0 or 4 kilograys of gamma radiation and stored for 8 d at 13-degrees- C. Radiolabeled breakdown products obtained from the metabolism of (16 :0/18:2)-phosphatidylcholine and (16:0/16:0)-phos-phatidyl-[N-methyl- H-3]choline by microsomal membranes indicated that phospholipase D (EC 3.1.4.4), phosphatidic acid phosphatase (EC 3.1.3.4), and lipolytic a cyl hydrolase were associated with the membranes. The rate of phosphat idylcholine catabolism by the membranes increased slowly in control ca uliflower during storage. Gamma irradiation caused an immediate rise i n phosphatidylcholine catabolism that remained higher than that of the controls during subsequent storage. Collectively, the data suggest th at enhancement of membrane lipolytic activity results from free-radica l-induced stress. Rapid increase of the membrane-associated phospholip ase D activity may be a key event leading to accelerated membrane dete rioration following gamma irradiation.