Factors affecting steroid and prostaglandin secretion by reproductive tissues of cycling and pregnant sows in vitro

Mitochondrial, microsomal and pellicular membranes were isolated from Tetrahymena cells grown at 39 degrees C or 15 degrees C, and phospholipids, in turn, were separated from total lipids extracted from these membranes. The effect of growth temperature on their solid-to-fluid phase transition temperature was examined by wide-angle X-ray diffraction. The transition temperatures of phospholipids from mitochondria, microsomes and pellicles were 21, 19 and 26 degrees C for cells grown at 39 degrees C and -8, -3 and 6 degrees C for cells grown at 15 degrees C, respectively. All phospholipids were found in a completely fluid state at these growth temperatures. From a comparison between the phospholipids and total lipids from pellicles of cells grown at 39 degrees C, a triterpenoid alcohol, tetrahymanol, caused the transition temperature to increase. The alignment of tetrahymanol in membranes was examined with pellicle'a total lipid oriented in a sample holder.     

Membrane lipid unsaturation modulates processing of the photosystem II reaction-center protein D1 at low temperatures.

The role of membrane lipid unsaturation in the restoration of photosystem II (PSII) function and in the synthesis of the D1 protein at different temperatures after photoinhibition was studied in wild-type cells and a mutant of Synechocystis sp. PCC 6803 with genetically inactivated desaturase genes. We show that posttranslational carboxyl-terminal processing of the precursor form of the D1 protein is an extremely sensitive reaction in the PSII repair cycle and is readily affected by low temperatures. Furthermore, the threshold temperature at which perturbations in D1-protein processing start to emerge is specifically dependent on the extent of thylakoid membrane lipid unsaturation, as indicated by comparison of wild-type cells with the mutant defective in desaturation of 18:1 fatty acids of thylakoid membranes. When the temperature was decreased from 33 degrees C (growth temperature) to 18 degrees C, the inability of the fatty acid mutant to recover from photoinhibition was accompanied by a failure to process the newly synthesized D1 protein, which accumulated in considerable amounts as an unprocessed precursor D1 protein. Precursor D1 integrated into PSII monomer and dimer complexes even at low temperatures, but no activation of oxygen evolution occurred in these complexes in mutant cells defective in fatty acid unsaturation.     

Chilling-induced photoinhibition in nine isolates of Valonia utricularis (Chlorophyta) from different climate regions

Chilling induced inhibition of photosynthesis was studied in nine isolates of the marine tropical to warm-temperate green macrophyte Valonia utricularis (Roth) C. Agardh. According to their temperature requirements for growth and survival, the isolates belong to a cold-tolerant Atlantic/Mediterranean group and a cold-sensitive Indo-west Pacific group. After 5 hours exposure to 5 degrees C under moderate light, all isolates experienced similar substantial photoinhibition, which approached steady state levels after a decline in Fv/Fm to about 40% of the initial values. After return to optimal temperature and dim light conditions, Fv/Fm values increased with biphasic kinetics. A fast phase with half-life times of less than 30 minutes (dynamic photoinhibition) was followed by a slow phase lasting a few hours, indicating repair of photodamaged PSII reaction centres (chronic photoinhibition). In the Atlantic/Mediterranean isolates the fast phase accounted for more than 80 % of the recovery response, showing that these isolates were able to cope with the applied low temperature stress by down-regulating their PSII reaction centres. In contrast, the two isolates from the Seychelles were predominantly photodamaged. In a second experiment, three isolates (Corsica, Seychelles, Japan) were exposed to a similar relative amount of cold stress (0, 10, 15 degrees C, respectively). The Japanese isolate and the isolate from the Seychelles showed significantly less inhibition compared to 5 degrees C exposure, but no significant difference was found in the Corsican isolate. However, the degree of low temperature stress had no significant influence on the relative contributions of dynamic and chronic photoinhibition. Only two of the seven investigated isolates had a lower final inhibition level when grown at sub-optimal temperatures than at optimal temperatures. However, all sub-optimally grown Atlantic/Mediterranean isolates exhibited faster recovery kinetics from chilling-induced photoinhibition than optimally grown plants. This is related to a faster recovery from chronic photoinhibition than to a higher relative contribution of dynamic photoinhibition. A specific role of the photoprotective pigments of the xanthophyll cycle, leading to an acclimation response in the Atlantic/Mediterranean isolates may be involved. We conclude that ecotypic differentiation in V. utricularis is mirrored in different degrees of susceptibility to low temperature stress.     

Acclimation to the growth temperature and thermosensitivity of photosystem II in a mesophilic cyanobacterium, Synechocystis sp. PCC6803

Differences in the temperature dependence and thermosensitivities of PSII activities in Synechocystis sp. PCC6803 grown at 25 and 35 degrees C were studied. Hill reactions in cells, thylakoid membranes and purified PSII core complexes were measured at high temperatures or at their growth temperatures after high-temperature treatments. In the presence of 2,5-dichloro-p-benzoquinone as an electron acceptor, which can accept electrons directly from Q(A), the temperature dependence of the oxygen-evolving activity was almost the same in thylakoid membranes and in the purified PSII complexes from cells grown at 25 or 35 degrees C. When duroquinone, which accepts electrons only through Q(B) plastoquinone, was used as an electron acceptor, the temperature dependence was the same for purified PSII core complexes but was different between thylakoids isolated from the cells grown at 25 and 35 degrees C. No remarkable difference was observed in protein compositions between thylakoids and between purified PSII complexes from cells grown at 25 or 35 degrees C. However, the fluidity of thylakoids, measured by electron flow to P700, was affected by the growth temperature. These results suggest that one of the major factors which cause the changes in the thermosensitivity of PSII is the change in the fluidity of thylakoid membranes. As for the acclimation of PSII in thylakoids to high temperatures, one of the main causes is the decrease in the high-temperature-induced formation of non-Q(B) PSII due to the decreased fluidity in the cells grown at 35 degrees C.     

Relationship between growth temperature of Anacystis nidulans and phase transition temperature of its thylakoid membranes

The temperatures of the lipid phase transition at which the solid phase disappears were determined by using the X-ray diffraction method in thylakoid membranes of the blue-green alga, Anacystis nidulans. The temperatures were determined as 26 and 16°C for cells grown at 38 and 28°C, respectively.     

Effect of growth temperature on membrane dynamics in a thermophilic cyanobacterium: a spin label study

A strain of Synechococcus sp. was grown at its optimal growth temperature (58 degrees C) and at 38 degrees C, in order to investigate possible adaptations of membrane-related properties to growth temperature. Light-induced electron transport in thylakoid membranes from both types of cells showed linear Arrhenius plots with the same activation energy (48 kJ/mol). Membranes from cells grown at 58 degrees C had a higher temperature optimum (53 degrees C) than those from cells grown at 38 degrees C (41 degrees C). Growth at 38 degrees C caused an increase in the proportion of unsaturated fatty acids compared to growth at 58 degrees C. The fluidity of the membranes was investigated by measuring the temperature dependence of the parameters derived from electron spin resonance spectra of the spin-labels 5-doxyldecane, 5-doxylstearate and 16-doxylstearate. Only small differences between the dynamic properties of the membranes from cells grown at different temperatures could be detected. This suggests that the observed change in fatty acid composition of the membranes following the change in growth temperature does not serve to maintain a constant viscosity at the growth temperature.     

An X-ray diffraction study on phase transition temperatures of various membranes isolated from Tetrahymena pyriformis cells grown at different temperatures

Mitochondrial, microsomal and pellicular membranes were isolated from Tetrahymena cells grown at 39°C or 15°C, and phospholipids, in turn, were separated from total lipids extracted from these membranes. The effect of growth temperature on their solid-to-fluid phase transition temperature was examined by wide-angle X-ray diffraction. The transition temperatures of phospholipids from mitochondria, microsomes and pellicles were 21, 19 and 26°C for cells grown at 39°C and ?8, ?3 and 6°C for cells grown at 15°C, respectively. All phospholipids were found in a completely fluid state at these growth temperatures. From a comparison between the phospholipids and total lipids from pellicles of cells grown at 39°C, a triterpenoid alcohol, tetrahymanol, caused the transition temperature to increase. The alignment of tetrahymanol in membranes was examined with pellicle's total lipid oriented in a sample holder.     

Acclimation of photosystem II to high temperature in a suspension culture of soybean (Glycine max) cells requires proteins that are associated with the thylakoid membrane

In a study of the responses of photosystem II (PSII) to high temperature in suspension-cultured cells of soybean (Glycine max L. Merr.), we found that high temperatures inactivated PSII via two distinct pathways. Inactivation of PSII by moderately high temperatures, such as 41°C, was reversed upon transfer of cells to 25°C. The recovery of PSII required light, but not the synthesis of proteins de novo. By contrast, temperatures higher than 45°C inactivated PSII irreversibly. An increase in the growth temperature from 25 to 35°C resulted in an upward shift of 3°C in the profile of the heat-induced inactivation of PSII, which indicated that the thermal stability of PSII had been enhanced. This acclimative response was reflected by the properties of isolated thylakoid membranes: PSII in thylakoid membranes from cells that had been grown at 35°C exhibited greater thermal stability than that from cells grown at 25°C. Disruption of the vesicular structure of thylakoid membranes with 0.05% Triton X-100 decreased the thermal stability of PSII to a similar level in both types of thylakoid membrane. Proteins released by Triton X-100 from thylakoid membranes from cells grown at 35°C were able to increase the thermal stability of Triton-treated thylakoid membranes. These observations suggest that proteins that are associated with thylakoid membranes might be involved in the enhancement of the thermal stability of PSII.     

Effects of bicarbonate and oxygen concentration on photoinhibition of thylakoid membranes

The effects of bicarbonate and oxygen on photoinhibition of thylakoid membranes were investigated by varying their concentrations independently of each other. A pretreatment of the thylakoid suspension which lowered the bicarbonate concentration of the medium without affecting its oxygen content, increased the degree of photoinhibition upon illumination. This showed that the normal bicarbonate content of a thylakoid suspension, originating from dissolved carbondioxide from the air, protects against photoinhibition. The resistance against photoinhibition was further increased by addition of extra NaHCO₃ up to about 5 mM. The normal oxygen content can be decreased profoundly without affecting the degree of photoinhibition; in contrast, even small changes from the normal bicarbonate content affected photoinhibition.At oxygen concentrations approximately below 25 M, added NaHCO₃ not only did not protect, but caused a more severe PS 2 inactivation. This was due to a blockage by added NaHCO₃ of the recovery from a reversible photoinhibited state.Furthermore, it is shown that if the bicarbonate ions bound to high-affinity sites in PS 2 were replaced by formate ions, the thylakoid membranes became less susceptible to photoinhibition under normal oxygen tension.Abbreviations chl chlorophyll - HEPES (N-[2-Hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]) - PpBQ phenyl-p-benzoquinone - PS 2 Photosystem 2 - Q_A and Q_B primary and secondary quinone acceptors of Photosystem 2     

The action in vivo of glycine betaine in enhancement of tolerance of Synechococcus sp. strain PCC 7942 to low temperature.

The cyanobacterium Synechococcus sp. strain PCC 7942 was transformed with the codA gene for choline oxidase from Arthrobacter globiformis under the control of a constitutive promoter. This transformation allowed the cyanobacterial cells to accumulate glycine betaine at 60 to 80 mM in the cytoplasm. The transformed cells could grow at 20 degrees C, the temperature at which the growth of control cells was markedly suppressed. Photosynthesis of the transformed cells at 20 degrees C was more tolerant to light than that of the control cells. This was caused by the enhanced ability of the photosynthetic machinery in the transformed cells to recover from low-temperature photoinhibition. In darkness, photosynthesis of the transformed cells was more tolerant to low temperature such as 0 to 10 degrees C than that of the control cells. In parallel with the improvement in the ability of the transformed cells to tolerate low temperature, the lipid phase transition of plasma membranes from the liquid-crystalline state to the gel state shifted toward lower temperatures, although the level of unsaturation of the membrane lipids was unaffected by the transformation. These findings suggest that glycine betaine enhances the tolerance of photosynthesis to low temperature.     

Protection against photooxidative damage provided by enzymatic and non-enzymatic antioxidant system in sorghum seedlings

Effect of photoinhibition of sorghum leaves and isolated chloroplasts on chlorophyll fluorescence, peroxidation of thylakoid lipids and activity of antioxidant enzymes were studied. Photoinhibition of intact leaves and isolated chloroplasts decreased Fv/Fm ratio and qP, while qN increased. Photoinhibitory damage was more at 5 degrees C than at 30 degrees or 50 degrees C. Peroxidation of thylakoid lipids was 5 times greater when photoinhibited at 50 degrees C compared to control. Photoinhibition of chloroplasts under low oxygen condition or when supplemented with anti-oxidants (beta-carotene, ascorbate and GSH) resulted in significantly less damage to photosynthesis (Fv/Fm ratio) and peroxidation level. Photoinhibition also resulted in many fold increase in the activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and decrease in catalase. Data presented here suggest that photoinhibition resulted in production of oxygen radicals and photoinhibition of chloroplasts in the presence of low oxygen level or when supplemented with antioxidants decreased the damage to Fv/Fm ratio and peroxidation level to a great extent since former prevented the formation of oxygen radicals and later could scavenge the oxygen radicals thus the protection. Increase activity of SOD and APX may also be to metabolise the oxygen radicals produced during photoinhibition treatment, thereby, protecting the seedlings against photooxidative damage.     

CHANGES IN PHOTOSYNTHESIS IN RESPONSE TO COMBINED IRRADIANCE AND TEMPERATURE STRESS IN CYANOBACTERIAL SURFACE WATERBLOOMS1

Buoyant cyanobacteria, previously mixed throughout the water column, float to the lake surface and form a surface waterbloom when mixing subsides. At the surface, the cells are exposed to full sunlight, and this abrupt change in photon irradiance may induce photoinhibition; at the same time, temperature rises as well. This study investigated the damaging effects of this increase in temperature as well as the ecologically more relevant combination of both an increased temperature and a high photon irradiance. Analysis of surface blooms with oxygen microelectrodes showed that integrated oxygen contents that are dependent on the balance of photosynthetic oxygen evolution and respiratory oxygen uptake decreased when temperature was raised above the lake temperature. Gross rates of photosynthesis were unaffected by temperatures up to of 35°C; hence, a moderate increase in temperature mainly stimulated oxygen uptake. Preincubation of cells of the cyanobacterium Anabaena flos-aquae (Lyngb.) de Brébisson at temperatures up to 35°C did not affect the subsequent measurement of rates of net photosynthesis. Another 5°C rise in temperature severely damaged the photosynthetic apparatus. Failure to restore net rates of photosynthesis was coupled to a strong quenching of the ratio of variable to maximum fluorescence, F_v/F_m, that was the result of a rise in F_o. A combination of high temperature and high photon irradiance was more damaging than high temperature alone. In contrast, low photon irradiances offered substantial protection against heat injury of the photosynthetic apparatus. I conclude from this study that because cyanobacteria usually are acclimated to low average irradiance prior to bloom formation, there is a reasonable risk of chronic photoinhibition. The increase in temperature will enhance the photodamage of cells in the top layer of the bloom. Low photon irradiances in subsurface layers will offer protection against heat injury. If the high temperatures extend to the deepest, dark layers of the bloom, damage in those layers is likely to occur.     

Relationship of growth temperature and thermotropic lipid phase changes in cytoplasmic and outer membranes from Escherichia coli K12.

Purified cytoplasmic and outer membranes isolated from cells of wild type Escherichia coli grown at 12, 20, 37 and 43 degrees C were labelled with the fatty acid spin probe 5-doxyl stearate. Electron spin resonance spectroscopy revealed broad thermotropic phase changes. The inherent viscosity of both membranes was found to increase as a function of elevated growth temperature. The lipid order to disorder transition in the outer membrane but not the cytoplasmic membrane was dramatically affected by the temperature of growth. As a result, the cytoplasmic membrane presumably existed in a gel + liquid crystalline state during cellular growth at 12 and 20 degrees C, but in a liquid crystalline state when cells were grown at 37 and 43 degrees C. In contrast, the outer membrane apparently existed in a gel + liquid crystalline state at all incubation temperatures. Data presented here indicate that the temperature range over which the cell can maintain the outer membrane phospholipids in a mixed (presumedly gel + liquid crystalline) state correlates with the temperature range over which growth occurs.     

Temperature dependence of the photosynthetic activities in the thylakoid membranes from the blue-green alga Anacystis nidulans

The photosynthetic electron transport and phosphorylation reactions were measured in the room temperature region in the thylakoid membranes prepared from the blue-green alga, Anacystis nidulans. The Arrhenius plot of the Hill reaction with 2,6-dichlorophenolindophenol showed a distinct break of straight lines at 21°C in the membranes from cells grown at 38°C, and at 12°C in those from cells grown at 28°C. The Arrhenius plot of the Hill reaction with ferricyanide showed a break at 13°C in the membranes from cells grown at 38°C, and at 7°C in those from cells grown at 28°C. On the other hand, the Arrhenius plot of the System I reaction with methylviologen as an electron acceptor and 2,6-dichlorophenolindophenol and ascorbate as an electron donor system was composed of a straight line in the membranes from cells grown at 28°C as well as at 38°C. The Arrhenius plot of the System II reaction measured by the ferricyanide reduction mediated by silicotungstate in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea also showed a break at 11°C in the membranes from cells grown at 38°C.The Arrhenius plot of the phosphorylation mediated by N-methylphenazonium methylsulfate showed a break at 21°C in the membranes from cells grown at 38°C and at 12°C in those from cells grown at 28°C. The Arrhenius plot of the phosphorylation mediated by the System I reaction showed a break at 24°C in the membranes from cells grown at 38°C.The characteristic features in the Arrhenius plots of the photosynthetic electron transport and phosphorylation reactions are discussed in terms of the transition of physical phase of the thylakoid membrane lipids.     

Photosynthetic activities of a thermophilic blue-green alga

Photosynthetic activities of a thermophilic blue-green alga,a species of Synechococcus, were studied with special referenceto its growth at high temperatures. A rapid algal growth occurredin the temperature range between 50 and 60?C, showing the maximumrate, six doublings per day, at about 57?C. Photosynthetic oxygenevolution and methyl viologen photoreduction in the cells werealso active at high temperatures and the optimum temperaturesfor these activities agreed with that of the algal growth. Thegrowth and photosynthetic activities were very low at room temperatureand irreversibly inactivated at temperatures above 60?C. The thylakoid membranes isolated from the alga were also photochemicallyactive at high temperatures. The membranes mediated ferricyanidephotoreduction coupled with a stoichiometric oxygen evolutionat a rate comparable to that of photosynthetic oxygen evolutionin the cells. The optimum temperature for the reaction was ashigh as 50?C. The membranes also showed a photosystem I-mediatedreaction at high temperatures. These observations indicate thatthe thylakoid membranes are intrinsically thermophilic in thisorganism. Thus the growth of the alga at high temperatures canbe well correlated to thermophilic properties of the photosyntheticapparatus. (Received February 20, 1978; )     

In vitro evidence for the involvement of activated oxygen in light-induced aggregation of thylakoid proteins

Protein aggregation in thylakoids incurred in situ during light-induced heat shock damage can be simulated in vitro by illuminating isolated thylakoids at normal temperatures. Aggregation is detectable in the in vitro model system by fluorography of [³⁵-S]-methionine-labelled thylakoids fractionated by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and also by Coomassie staining after SDS-PAGE of unlabelled thylakoids. As in the case of light-induced heat shock damage, protein aggregation in the in vitro system is completely light dependent, and the D-1 protein of PS][is present in the protein aggregate. The model system has also provided evidence for the involvement of activated oxygen in aggregation of thylakoid proteins. Histidine, which scavenges singlet oxygen, and n -propylgallate; a non-specific scavenger of activated oxygen, both provided complete protection against light induced protein aggregation in isolated thylakoids. These compounds also strongly reduced the levels of activated oxygen by illuminated thylakoids as measured by electron spin resonance. The involvement of activated oxygen is further supported by the finding that protein aggregation in the model system proved to be oxygen dependent. The herbicide dichlorophenyldimethyl urea, which binds to the QB site of the D-1 protein of PSII and provides protection against photoinhibition and light dependent degradation of the D-1 protein, also provided partial protection against protein aggregation in the in vitro system. Protein continues to aggregate after PSII activity has reached undetectable levels suggesting that aggregation is a consequence rather than a cause of photoinhibition. The observations collectively indicate that aggregation of thylakoid proteins is attributable to activated oxygen.     

Photoinhibition and recovery of photosynthesis in intact barley leaves at 5 and 20°C

Photoinhibition of photosynthesis and its recovery were studied in intact barley ( Hordeum vuigare L. cv. Gunilla) leaves grown in a controlled environment by exposing them to two temperatures, 5 and 20°C, and a range of photon flux densities in excess of that during growth. Additionally, photoinhibtion was examined in the presence of chloramphenicol (CAP, an inhibitor of chloroplast protein synthesis) and of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Susceptibility to photoinhibition was much higher at 5 than at 20°C. Furthermore, at 20°C. CAP exacerbated photoinhibition strongly, whereas CAP had little additional effect (10%) at 5°C. These results support the model that net photoinhibition is the difference between the inactivation and repair of photosystem II (PSII); i.e. the degradation and synthesis of the reaction centre protein, Dl. Furthermore, the steady-state extent of photoinhibition was strongly dependent on temperature and the results indicated this was manifested through the effects of temperature on the repair process of PSII. We propose that the continuous repair of PS II at 20°C conferred at least some protection from photoinhibition. At 5°C the repair process was largely inhibited, with increased photoinhibition as a consequence. However, we suggest where repair is inhibited by low temperature, some protection is alternatively conferred by the photoinhibited reaction centres. Providing they are not degraded, such centres could still dissipate excitation energy non-radiatively, thereby conferring protection of remaining photochemically active centres under steady-state conditions.
A fraction of PS II centres were capable of resisting photoinhibition when the repair process was inhibited by CAP. This is discussed in relation to PS II heterogeneity. Furthermore, the repair process was not apparently activated within 3 h when barley leaves were transferred to photoinhibitory light conditions at 20°C.     

Balancing photosynthetic light-harvesting and light-utilization capacities in potato leaf tissue during acclimation to different growth temperatures

We investigated the effect of temperature during growth and development on the relationship between light-harvesting capacity, indicated by chlorophyll concentration, and light-utilization potential, indicated by light- and bicarbonate-saturated photosynthetic oxygen evolution, in Solanum tuberosum L. cv. Norland. Conal plantles were transplanted and grown at 20°C for 2 weeks before transfer to 12, 16, 20, 24 and 28°C for 6 weeks. After 4 weeks of the temperature treatments, leaf tissue fresh weights per area were one-third higher in plants grown at 12°C vs those grown at 28°C. Conversely, chlorophyll content per area in tissue grown at 12°C was less than one-half of that of tissue grown at 28°C at 4 weeks. Photosynthetic capacity measured at a common temperature of 20°C and expressed on a chlorophyll basis was inversely proportional to growth temperature. Leaf tissue from plants grown at 12°C for 4 weeks had photosynthetic rates that were 3-fold higher on a chlorophyll basis than comparable tissue from plants grown at 28°C. These results suggest that the relationship between light-harvesting capacity and light-utilization potential varies 3-fold in response to the growth temperatures examined. The role of this response in avoidance of photoinhibition is discussed.     

Temperature-dependent changes in Photosystem II heterogeneity of attached leaves under high light

Attached leaves of pumpkin ( Cucurbita pepo L. cv. Jattiläismeloni) were exposed to high light intensity at room temperature (ca 23°C) and at 1°C. Fluorescence parameters and electron transport activities measured from isolated thylakoids indicated faster photoinhibition of PSII at low temperature. Separation of the α and β components of the complementary area above the fluorescence induction curve of dichlorophenyl-dimethylurea-poisoned thylakoids revealed that at low temperature only the α-centers declined during exposure to high light intensity while the content of functional β-centers remained constant. Freeze-fracture electron microscopy showed no decrease in the density of particles on the appressed exoplasmic fracture face, indicating that the photoinhibited α-centers remained in the appressed membranes at 1°C. Because of the function of the repair and protective mechanisms of PSII, strong light induced less photoinhibition at room temperature, but more complicated changes occurred in the α/β-heterogeneity of PSII. During the first 30 min at high light intensity the decrease in α-centers was almost as large as at 1°C, but in contrast to the situation at low temperature the decrease in α-centers was compensated for by a significant increase in PSIIβ-centers. Changes in the density and size of freeze-fracture particles suggest that this increase in β-centers was due to migration of phosphorylated light-harvesting complex from appressed to non-appressed thylakoid membranes while the PSII core remained in the appressed membranes. This situation, however, was only transient and was followed by a rapid decrease in the functionalβ-centers.     

Infrared spectroscopic study of the gel to liquid-crystal phase transition in live Acholeplasma laidlawii cells

The temperature dependences of the infrared spectra of deuterium-labeled plasma membranes of live Acholeplasma laidlawii B cells and of the isolated plasma membranes demonstrate that the profiles of the gel to liquid-crystal phase transitions are very different. At temperatures within the range of the phase transition, the live mycoplasma is able to keep the "fluidity" of its plasma membrane at a much higher value than that of the isolated plasma membrane at the same temperature. The difference is particularly pronounced at and around the temperature of growth. Live Acholeplasma laidlawii, grown at 37 degrees C on a fatty acid depleted medium supplemented with myristic acid (C14:0), pentadecanoic acid (C15:0), or palmitic acid (C16:0), are highly "fluid"; i.e., at the temperature of growth, the fractional population of the liquid-crystalline phase is 95-100% at 37 degrees C, whereas in the case of the isolated plasma membranes the fractional population of the liquid-crystalline phase at 37 degrees C is only 58% (C14:0), 36% (C15:0), or 38% (C16:0).