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Plant Physiology 69:1356-1360 (1982)
© 1982 American Society of Plant Biologists

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Thermal Behavior and Lipid Composition of Cauliflower Plasma Membranes in Relation to ATPase Activity and Chilling Sensitivity

Lesley C. Wright, Edward J. McMurchie1, M. Keith Pomeroy2 and John K. Raison

Plant Physiology Unit, Commonwealth Scientific and Industrial Research Organization, Division of Food Research and the School of Biological Sciences, Macquarie University, North Ryde, N.S.W., 2113, Australia

A plasma-membrane fraction rich in ion-stimulated ATPase activity was isolated from cauliflower (Brassica oleracea L.) buds. The activity of the ATPase was dependent on Mg2+ and stimulated 4-fold by K+. The lipids of the membrane fraction contained 57% by weight of phospholipid, 16% glycolipid including sterol glycosides, and 27% neutral lipids. Sterols and sterol esters comprised 9% by weight of the total lipid fraction, and the M ratio of total sterol to phospholipid was 0.5. Fatty acid unsaturation of the membrane lipids was 75%. Arrhenius plots of the Mg2+ and Mg2+ + K+ stimulated ATPase activity were biphasic with an increase in activation energy occurring below about 12°C, a response typical of some membrane-associated enzymes of chilling-sensitive plants. No thermal transitions were detected in the membranes or membrane lipids between 0 and 30°C using differential scanning calorimetry and electron spin resonance spectroscopy. This type of thermal behavior is typical of membranes of chilling-resistant plants. It was concluded that the low temperature increase in activation energy of the ion-stimulated, membrane-associated ATPase is an intrinsic property of the enzyme system and not the result of a transition in the bulk membrane lipid.

1 Present address: Commonwealth Scientific and Industrial Research Organization Division of Human Nutrition, Glenthorne Laboratory, O'Halloran Hill, S.A., 5158, Australia

2 Visiting Scientist from Chemistry and Biology Research Institute, Research Branch, Agriculture Canada, Ottawa, Canada. Contribution No. 1271 from Chemistry and Biology Research Institute.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1982 by the American Society of Plant Biologists