Abstract
Freezing tolerance is an important character for plants living under subzero temperatures in winter season. The growth of ice crystals or the freeze-induced dehydration mechanically may disrupt the plasma membrane. Many studies have indicated that the freezing tolerance is correlated with the cryostability of plasma membrane. Although, in animal cells, the mechanically disrupted plasma membrane is rapidly repaired dependently on the extracellular calcium, no report has been published on the plasma membrane repair in plant cells. It is expected that the cryostability of plasma membrane is tightly associated with the membrane repair manner. We studied the calcium-dependent survival of plant cell for mechanical stresses using Arabidopsis protoplasts isolated from control and cold-acclimated leaves. The tolerance to electric shock by the electroporator treatment which directly disrupted plasma membrane was also dependent on the extracellular calcium. The enhanced freezing tolerance was remarkably dependent on the extracellular calcium during freezing. Interestingly, the tolerance to dehydration caused by hyperosmotic solution was hardly dependent on the extracellular calcium. Finally, we estimate that the tolerance to mechanical stress caused by the ice crystal growth is dependent on the extracellular calcium.
