Chemical and Biophysical Changes in the Plasma Membrane during Cold Acclimation of Mulberry Bark Cells (Morus bombycis Koidz. cv Goroji)

The lipid and protein composition of the plasma membrane isolated from mulberry (Morus bombycis Koidz.) bark cells was analyzed throughout the cold acclimation period under natural and controlled environment conditions. There was a significant increase in phospholipids and unsaturation of their fatty acids during cold acclimation. The ratio of sterols to phospholipids decreased with hardiness, primarily due to the large increase in phospholipids. The fluidity of the plasma membrane, as determined by fluorescent polarization technique, increased with hardiness. Electrophoresis of plasma membrane proteins including glycoproteins revealed change in banding pattern during the early fall to winter period. Some of the protein changes could be related to growth cessation and defoliation. However, minor changes in proteins also occurred during the most active period of hardening. Changes in glycoproteins were coincident both with changes in growth stages and with the development of cold hardiness.