Dynamics and Cryo-observation of the Endoplasmic Reticulum of Plants

Abstract

Many plants which experience subzero temperatures in winter increase freezing tolerance by exposure to non-freezing temperature, a phenomenon known as cold-acclimation. Recently, using a confocal fluorescent microscopy with cryostage, we found the extracellular freezing-induced membrane dynamics (cryodynamics) of the endoplasmic reticulum (ER) in cells of Welsh onion which can survive the winter below -40°C. For example, the extracellular freezing quickly led to stop the streaming of ER networks and then the networks collapse into vesicles. Furthermore, in cold-acclimated cells, the networks and streaming of ER are recovered within one hour after thawing. In this study, we focused on the generality of this cryodynamics in various plants which were collected in and near Iwate University in Morioka. In herbaceous plants sampled in winter, the streaming of ER networks was observed at nonfreezing temperatures, but in woody plants sampled from winter to summer the ER streaming was not observed. The ER streaming in herbaceous plant cells was quickly stopped by extracellular freezing but not by supercooling, while the freeze-induced ER vesiculation was not observed. In woody plants, the ER cryodynamics like that observed in herbaceous plants was not observed. Taken together, our results indicate that the extracellular freezing generally may result in the stop of ER streaming if ER streaming occurs in cells in the nonfreezing condition.