Abstract
Differential thermal analyses revealed that a large low temperature exotherm (LTE) initiated at temperatures around -20C. To reveal the mechanism of cold hardiness or deep supercooling in the leaves of this species, we observed the freezing process of leaf blades and leaf sheath using cryomicroscopy. The large LTE released from the leaf blade is most likely a combination of multiple freezing events: all the mesophyll cells in a tissue unit froze together in two sequential incidents (indicated by darkening of the units) and tissue units randomly froze one after another while other type of cells froze independently one after another (some of which were accompanied by bubble formation). Both types of freezing events were most likely to be intracellular freezing. LTE corresponded well with the injury of the tissues. The large LTE released from the leaf sheath arose from the random (intracellular) freezing of cell clusters. The tissue was not separated by lateral veins but the cluster of cells froze together (cluster size was different in a freezing incident from another) LTE corresponded well with the injury of the tissues.
