Abstract
Many plants living under subzero temperatures in winter acquire freezing tolerance by exposed non-freezing temperature. This phenomenon, known as cold-acclimation, involves many complex processes. In cold-acclimated cells, unique cryobehaviors of the plasma membrane and endoplasmic reticulum (ER) have been reported, the physiological meaning of which is unknown.
From Allium fistulosum of a hardy onion species grown in Saskatchewan, Canada, which survives winter of-40 C, intact single cell epidermal layers in leaf sheath are easily peeled. The cryobehavior of ER in these epidermal cells was observed by using a confocal fluorescent microscopy with cryostage and the ER-selective fluorescent dye (ER-Tracker). According to our observations, cold-acclimation increased ER and freezing induced ER vesiculation through the breakdown in the ER network. Freeze-induced ER vesicles in cold-acclimated cells were larger and more abundant than those in non-acclimated cells, which appeared to be largely fragmented. After thawing, the ER network partially recovered only in cold-acclimated cells, suggesting that the cryobehavior of ER may be associated with the acquired freezing tolerance.
