A freeze-fracture study of the influence of frost hardening treatments on the plasma membranes of Medicago sativa and Bromus inermis cell suspension cultures

Abstract

Freeze-fractured suspension cultured cells of alfalfa (Medicago sativa L.) and bromegrass (Bromus inermis Leyss) were examined before and after frost hardening treatments for evidence of plasma membrane adaptation to frost. No chemical fixatives or cryoprotective agents were used and care was taken to ensure that there was no subjective bias in making counts of intramembrane particles. There were no patches of membrane free of intramembrane particles in any of the treatments, and only small differences in intramembrane particles frequencies were found. Cold hardening and abscisic acid hardening may have had different effects on intramembrane particles frequency, but because of the low level of statistical significance this was uncertain. Two arrays of membrane particles (strings and rosettes) were present in all treatments. It is concluded that the technique may be insufficiently sensitive to detect the subtle changes in membrane protein composition that probably accompany adaptation to frost. Key words: Medicago sativa, Bromus inermis, frost hardiness, membrane structure, freeze-fracture.