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Environmental and Stress Physiology

Delay of Membrane Lipid Degradation by Calcium Treatment during Cabbage Leaf Senescence ¹

Département de Sciences et Technologie des Aliments, Pavillon Comtois, Université Laval, Québec, QC, Canada, G1K 7P4, Centre de Recherche et de Développement sur les Aliments, Agriculture Canada, 3600 Boulevard Casavant O., Saint-Hyacinthe, QC, Canada, JS2 8E3

Cabbage leaf discs (Brassica oleracea L., Capitata group) were floated adaxial side up in 0, 0.05, or 0.25 M CaCl₂ solutions at 15°C for 14 d in the dark. To assess whether the delay of senescence by calcium treatment involved protection of membrane lipids, chlorophyll and protein content and the lipid composition of the membranes were determined during incubation. Chlorophyll and protein content decreased with time, in correlation with a reduction in the amount of phospholipids. The degree of unsaturation of phospholipids and free fatty acids decreased, whereas the ratio of sterol to phospholipid increased. The proportions of phospholipid classes did not change during senescence. The catabolism of phospholipids was delayed by 0.05 M calcium, but accelerated by 0.25 M, as compared to the untreated control. Based on the levels of the lipid intermediates, phospholipase D, phosphatidic acid phosphatase, lipolytic acyl hydrolase, and lipoxygenase appeared to be involved in the breakdown of phospholipids during senescence. Phospholipase D and phosphatidic acid phosphatase may be directly influenced by calcium. The calcium treatment apparently did not affect the activity of acyl hydrolase. Lipoxygenase, responsible for the peroxidation of the polyunsaturated fatty acids, was probably indirectly influenced by calcium. We conclude that the delay of senescence of cabbage leaf discs by calcium treatment involved protection of membrane lipids from degradation.

¹ This research was supported by the Conseil des Recherches en Pêche et Agro-alimentaire du Québec and the Natural Sciences and Engineering Research Council of Canada. Contribution No. 263 from the Centre de Recherches et de Développement sur les Aliments, Agriculture Canada, Saint-Hyacinthe. Contribution No. 61 from the Centre de Recherches en Horticulture, Université Laval.

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