PLANT PHYSIOLOGY , Vol 111, Issue 1 301-312, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Effects of COR6.6 and COR15am Polypeptides Encoded by COR (Cold-Regulated) Genes of Arabidopsis thaliana on Dehydration-Induced Phase Transitions of Phospholipid Membranes
M. S. Webb, S. J. Gilmour, M. F. Thomashow and P. L. Steponkus
Department of Soil, Crop and Atmospheric Sciences, Cornell University, Ithaca, New York 14853 (M.S.W., P.L.S.)
Cold acclimation of Arabidopsis thaliana includes the expression of
cold-regulated (COR) genes and the accumulation of COR polypeptides. The
hydration characteristics of two COR polypeptides, COR6.6 and COR15am, have
been determined and their effects on the dehydration-induced liquid
crystalline-to-gel and lamellar-to-hexagonal II phase transitions in
phospholipid mixtures have been examined. After dehydration at osmotic
pressures between 8 and 150 MPa, the water content of the COR polypeptides
was less than that of bovine serum albumin, with COR15am the least
hydrated: bovine serum albumin > COR6.6 > COR15am. Neither COR6.6 nor
COR15am altered the dehydration-induced gel lamellar -> fluid lamellar
phase transition temperature of either dipalmitoylphosphatidylcholine or
dioleoylphosphatidylcholine (DOPC). In multilamellar vesicles of
dioleoylphosphatidylethanolamine:DOPC (1:1, mol:mol) prepared by either
freeze-thaw or reverse-phase evaporation methods, neither COR6.6, COR15am,
nor bovine serum albumin altered the incidence of the dehydration-induced
formation of the inverted hexagonal phase as a function of osmotic
pressure. However, a specific ultrastructural alteration[mdash] the
formation of a striated surface morphology in the lamellar
domains[mdash]was observed in mixtures of
dioleoylphosphatidylethanolamine:DOPC that were dehydrated in the presence
of COR15am. Nevertheless, neither COR6.6 nor COR15am appears to participate
in a specific protein-phospholipid interaction that alters the
dehydration-induced phase behavior of phospholipid vesicles.