Maintenance of Membrane Fluidity during Development of Freezing Tolerance of Winter Wheat Seedlings

ABSTRACIPermeability coefficients (Kp) of nonelectroytes were determined at several temperatures for nonacclimated and acclimated plasma membranes of the frost sensitive Solanum tuberosum and the frost resistant Solanum commersonii. In nonacclimated membranes, Kp were equal at 25°C for the two species. Kp decreased with decreased temperature in both species; however, the decrease was much greater in the frost sensitive S. tuberosum than in frost resistant S. commersonii.Kp increased with cold acclimation. After acclimation the temperature sensitivity of Kp or activation energy (Ea) for S. tuberosum was similar to that of S. commersonii; however, Kp for S. tuberosum were lower than those for S. commersonii at all temperatures.The differences in Kp and activation energy indicate plasma membrane differences between the species before acclimation. After acclimation there was still a difference between the plasma membranes of the two species as well as a difference between the nonacclimated and acclimated membranes of the same species.

Section: Discussioncontrasting

confidence: 55%

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confidence: 99%

Temperature Response of Plasma Membranes in Tuber-Bearing Solanum Species

Fennell¹,

Li²

1986

“…Although this concept has been accepted widely, recently it has been questioned in view of the apparent similarity in whole root membrane fluidity and the transition temperature of membrane lipids demonstrated with several wheat cultivars grown at 2 and 22°C (17). Other reports (3,6,9,16) also have suggested that changes in fatty acid composition of membranes are not required for cold acclimation of a number of plant species.…”

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confidence: 99%

“…The DBI values of lipids from old and new roots increased with time at all temperatures (Table III). In old roots, DBI values were not different among tempera- (3,6,9,16,17) …”

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confidence: 99%

Fatty Acid Composition and Nitrate Uptake of Soybean Roots during Acclimation to Low Temperature

Osmond

Wilson²,

Raper³

1982

Fatty acid composition of old and new roots was determined for soybeans (Glycine max IL.I Merr. cv Ransom) at root-zone temperatures of 14, 18, and 22°C during a 26-day period. New roots had a greater concentration of polyunsaturated fatty acids than old roots. The ratio of polyunsaturated to saturated fatty acid concentration in new roots exposed to 14 and 18°C peaked at 16 days and declined, while the corresponding ratio in old roots increased throughout the treatment period. Apparently the response of fatty acid composition in old and new roots to low temperature was mediated by tissue aging or differentiation. These findings were contrary to the concept that modifications in fatty acid composition remain constant at lower temperatures.The function of root tissues exposed to lower temperature was evaluated with respect to the ability of the root systems to absorb N03-. Over the relatively long periods of exposure, the ability of whole root systems to absorb N03-was similar at cool and warm temperatures. The effect of cool temperature on functioning of roots appeared to involve reductions in the rates of initiation and differentiation of young root tissues rather than changes in membrane permeability related to alteration of fatty acid composition.Biological membranes require a fluid physical state to function (23). The fluidity of biological membranes may be governed by metabolic regulation of lipid composition (23). In response to external stimuli, such as temperature, changes in metabolism and acyl-lipid saturation of membranes often are observed (2,7,11). In root tissues of several species (1,5,9,12,18,21,22), the ratio of polyunsaturated to saturated fatty acid concentration generally increases with decreases in temperature. At low temperature, a decrease in membrane fluidity enhances polyunsaturated fatty acid formation, while at higher temperatures an increase in fluidity favors the synthesis of saturated acyl-units (10, 23

“…Figure 4 shows plots for the effect of temperature on the motion of 1,14) in aqueous dispersions of pure DPPC, melting point 41C, and in mixtures of DPPC and polar lipids from wheat roots which on their own show a transition at -6°C (19). Since the plots for the pure DPPC and the mixtures containing up to 50% DPPC appear to consist of two linear segments connected by a curve, the data were analyzed by two methods: (a) by fitting straight lines and determining the temperature at which there is a significant increase in the temperature coefficient of spin label motion (slope) as temperature decreases and (b) fitting the data to an equation developed by Klein (10) to define rate processes in membranes.…”

mentioning

confidence: 99%

Phase Transitions in Thylakoid Polar Lipids of Chilling-Sensitive Plants

Raison

Orr²

1986

Self Cite

The phase behavior of thylakoid polar lipids from plants sensitive to chiling injury was investigated by calorimetry, electron spin resonance spectroscopy of spin labels, and fluorescence intensity after labeling with trans-parinaric acid. The plants used were oleander (Nerium olader), mung bean (Vigna radiata L. var Mungo), and tomato (Lycopersicon esculentum cv Grosse Lisse). For all plants the initiation temperature for the calorimetric exotherm was coincident (±1lC) with the transition determined by the increase in the temperature coefficient of spin label motion and fluorescence intensity of trans-parinaric acid. For oleander plants, grown at 45°C, the transition was at 7°C while for plants from the same clone, grown at 20°C, it was at -2°C. For mung bean and tomato the transition was between 9 and 12°C. The similarity in the transition detected by spin labeling and fluorescence intensity suggest that spin labels, like the fluorescent label traws-parinaric acid, preferentially partition into domains of ordered lipid. The coincidence of the temperature for initiation of the transition, determined by the three techniques, shows that each is a valid method of assessing a phase transition in membrane polar lipids.It has been proposed that chilling-injury is initiated by a thermally-induced transition in the structure or phase state of some ofthe lipids which constitute the bilayers ofcell membranes (11,12,23). Evidence supporting this hypothesis has relied mainly on the correlation between the critical temperature below which the plant is injured and the temperature of the lipid phase transition detected indirectly using either spin (21, 22) or fluorescent (24) probes.This explanation of the primary cause of chilling injury has not been universally accepted. The principal objection is that the phase transition is inferred from a change in the temperature coefficient of motion ofa spin probe (28) intercalated with either mitochondria or chloroplast membranes or liposomes formed from the lipids of these membranes (6,22). Furthermore, this inference relating the change in the temperature coefficient of probe motion to a phase transition has been criticized on the grounds that probes can form impurity pools within the host lipids and have the potential to perturb the system being analyzed (3,28). In addition, motion ofthe spin probe is usually calculated using an equation which depends on the probe undergoing isotropic motion (9) but it has been noted that motion of the nitroxide-type probes, commonly used in these studies with membrane lipids, is rarely isotropic (28). Thus, the motion parameter calculated from the electron spin resonance spectra of probes in membrane lipids could represent the summation of segmental, diffusion, and vibrational motion as well as a component influenced by the ordering ofthe probe in the membrane lipids (28). Under these conditions the motion parameter could increase markedly as membrane lipids become more ordered at low temperature even though no transition occurred in the ...