Occurrence of glass transitions in long-chain phosphatidylcholine mesophases.

Several phosphatidylcholine (PC) species were studied by differential scanning calorimetry at different levels of hydration. A glass transition was observed in both lamellar gel and nonlamellar phases, with the glass transition temperature, T(g), decreasing as water content was increased. The structure of the lipid mesophase has a major impact on T(g), with the lamellar gel phase having a higher T(g) than that of nonlamellar phases of the same lipid.

Freezing sensitivity in the sfr4 mutant of Arabidopsis is due to low sugar content and is manifested by loss of osmotic responsiveness.

Protoplasts were tested to determine whether the freezing sensitivity of the sfr4 (sensitive to freezing) mutant of Arabidopsis was due to the mutant's deficiency in soluble sugars after cold acclimation. When grown under nonacclimated conditions, sfr4 protoplasts possessed freezing tolerance similar to that of wild type, with the temperature at which 50% of protoplasts are injured (LT(50)) of -4.5 degrees C.

Phase behavior and glass transition of 1,2-dioleoylphosphatidylethanolamine (DOPE) dehydrated in the presence of sucrose.

The effect of sucrose on the phase behavior of 1,2-dioleoylphosphatidylethanolamine (DOPE) as a function of hydration was studied using differential scanning calorimetry and X-ray diffraction. DOPE/sucrose/water dispersions were dehydrated at osmotic pressures (Pi) ranging from 2 to 300 MPa at 30 degrees C and 0 degrees C. The hexagonal II-to-lamellar gel (H(II)-->L(beta)) thermotropic phase transition was observed during cooling in mixtures dehydrated at Pi View Article and Find Full Text PDF

Phase diagram of 1,2-dioleoylphosphatidylethanolamine (DOPE):water system at subzero temperatures and at low water contents.

The phase behavior of partially hydrated 1, 2-dioleoylphosphatidylethanolamine (DOPE) has been studied using differential scanning calorimetry and X-ray diffraction methods together with water sorption isotherms. DOPE liposomes were dehydrated in the H(II) phase at 29 degrees C and in the L(alpha) phase at 0 degrees C by vapor phase equilibration over saturated salt solutions. Other samples were prepared by hydration of dried DOPE by vapor phase equilibration at 29 degrees C and 0 degrees C.

Mode of action of the COR15a gene on the freezing tolerance of Arabidopsis thaliana.

Constitutive expression of the cold-regulated COR15a gene of Arabidopsis thaliana results in a significant increase in the survival of isolated protoplasts frozen over the range of -4.5 to -7 degreesC. The increased freezing tolerance is the result of a decreased incidence of freeze-induced lamellar-to-hexagonal II phase transitions that occur in regions where the plasma membrane is brought into close apposition with the chloroplast envelope as a result of freeze-induced dehydration.