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

Abstract

A plasma-membrane fraction rich in ion-stimulated ATPase activity was isolated from cauliflower (Brassica olerwea L.) buds. The activity of the ATPase was dependent on Mg2" and stimulated 4-fold by KV. 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 Mg2e + K+ stimulated ATPase activity were biphasic with an increase in activation energy occurring below about 12°C, a response typical of some membraneassociated 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 chillingresistant 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.Many membrane-bound enzymes associated with mitochondria and chloroplasts of chilling-sensitive plants show nonlinear Ar-rhenius plots with an increase in Ea' below about 10°C (12,23 23) and together they provide a molecular explanation of chilling injury (12). Some soluble enzymes also exhibit nonlinear Arrhenius plots at low temperatures. This can be explained on the basis of a direct, temperature-induced, reversible alteration in the tertiary structure of the enzyme or the enzyme-substrate complex (4). Examples from plants include some key enzymes of carbon metabolism, such as P-enolpyruvate carboxylase (7), but the role of these enzymes in the development of chilling injury has yet to be elucidated. Furthermore, some membrane-associated enzymes from chilling-resistant plants also exhibit nonlinear Arrhenius plots, e.g. the photoreduction of DCIP by chloroplasts from barley (17) and pea (18), assayed in the presence ofuncouplers. However, no phase separation (21) or change in lipid ordering (24) occurs in the membranes of these plants at temperatures coincident with the altered activation energies and such changes are more likely a direct effect of temperature on the uncoupler-enzyme-substrate complex. Inasmuch as growth of barley and pea continue well into the chilling temperature range, the altered enzyme kinetics observed in vitro at chilling temperatures have little influence on growth and development of these plants. These observations stress the importance of establishing whether tissue metabolism reflects the altered kinetics of the isolated enzyme systems before such changes are causally linked to chilling injury.The question of the relative contribution of changes in enzyme kinetics and/or changes in membrane lipid order to chilling injury is complicated with...

Purification of plasma membranes from leaves of conifer and deciduous tree species by phase partitioning and free-flow electrophoresis

“…The plasma membrane has also been shown to play an important role in cold acclimation, freezing injury and chilling stress in different plant tissues (Hellergren et al, 1984, Kuiper 1985, Wright et al, 1982 and much evidence supports the hypothesis that environmental stresses such as low temperature, water stress, wounding, infection, drought, pollution, are al! mediated by changes in the redox status of the tissues Heath 1990, Penel andCastillo 1989),…”

Impact of increased membrane realism on conformational sampling of proteins

“…Fatty acid chain distributions for each headgroup were estimated only from sources where mass spectrometry information was provided on both the sn-1 and sn-2 acyl chains. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] To make this membrane as realistic as possible, we wanted to account for leaflet asymmetry. In terms of asymmetric lipid distribution across different leaflets within the plant plasma membrane, literature is limited; specifically, it has been reported that the distributions of lipid species across the plasma membrane upper:lower leaflets are 35:65 and 70:30 for phospholipids and sterols, respectively.…”

Lipid Profiles of Leaf Tonoplasts from Plants with Different CO2‐Fixation Mechanisms*

“…44mol YO were found (Wright et al, 1982;Yoshida and Uemura, 1986;Lynch and Steponkus, 1987;Rochester et al, 1987). However, the data show that in contrast to animal cells free sterols cannot be used as markers for plasma membranes in plant cells.…”

“…The group of lipids characteristic of tonoplasts are the glucolipids ASG, CER and SG which are also found in plasma membranes (Wright et al, 1982;Yoshida and Uemura, 1986;Lynch and Steponkus, 1987;Rochester et al, 1987). They amounted to about 20-30mole % ofthe total lipids in mechanically and 31-37 % in enzymatically isolated tonoplasts (Table 1).…”

“…Thylakoid membranes are characterized by the predominance of galactolipids which are supplemented by small proportions of sulfo-and phospholipids, whereas microbodies and mitochondria are devoid of glycolipids and instead have a whole complement of phospholipids. Plasma membranes (Wright et al, 1982;Yoshida and Uemura, 1986;Lynch and Steponkus, 1987;Rochester et al, 1987) and tonoplasts (Verhoek et al, 1983;Yoshida and Uemura, 1986) are characterized by another unique lipid composition. They contain, in addition to phospholipids, glucolipids and free sterols.…”