Effects of Cold Acclimation on the Morphological and Physiological Properties of Alfalfa ( Medicago sativa) Suspension Culture Cells

Abstract

Cell suspension cultures of alfalfa (Medicago sativa L. cv. Rangelander) maintained at 2°C for 14 days were much more resistant to freezing-induced damage than cultures maintained at 21 °C. While no gain in fresh weight occurred during acclimation, such cells had smaller vacuoles and appeared to have more membranous material in their cytoplasm. The latter observation was supported by cell fractionation studies which indicated that the acclimated cells contained more microsomal phospholipid and protein than control cells. In contrast, the total solute content was lower in acclimated compared to control cells. Acclimation increased the relative content of phospholipids and decreased the sterol content of membranes. Also the phospholipids of acclimated cells had a higher percentage of unsaturated fatty acyl chains than those of control cells. As a result, the fluidity of liposomes prepared from membrane lipids, measured by fluorescence depolarization, was higher for preparations from acclimated cells than the control cells. The results suggest that membrane modification, during low temperature culture, is a major component of the cold acclimation process in alfalfa cells and that the adjustments which occur in the solute and water content of the cells are minor components of the process.