Roles of cell walls and intracellular contents in supercooling capability of xylem parenchyma cells of boreal trees

Abstract

The supercooling capability of xylem parenchyma cells (XPCs) in boreal hardwood species differs depending not only on species, but also season. In this study, the roles of cell walls and intracellular contents in supercooling capability of XPCs were examined in three boreal hardwood species, Japanese beech, katsura tree and mulberry, whose supercooling capability differs largely depending on species and season. XPCs in these species harvested in winter and summer were treated by rapid freezing and thawing (RFT samples) or by RFT with further washing (RFTW samples) to remove intracellular contents from XPCs in order to examine the roles of cell walls in supercooling. RFT samples were also treated with glucose solution (RFTG samples) to examine roles of intracellular contents in supercooling. The supercooling capabilities of these samples were examined by differential thermal analysis after ultrastructural observation of XPCs by a cryo-scanning electron microscope to confirm effects of the above treatments. XPCs in RFTW samples showed a large reduction in supercooling capability to similar temperatures regardless of species or season. On the other hand, XPCs in RFTG samples showed a large increase in supercooling capability to similar temperatures regardless of species or season. These results indicate that although cell walls have an important role in maintenance of supercooling, change in supercooling capability of XPCs is induced by change in intracellular contents, but not by change in cell wall properties.

Presence of supercooling-facilitating (anti-ice nucleation) hydrolyzable tannins in deep supercooling xylem parenchyma cells in Cercidiphyllum japonicum

“…Recent studies have indicated that fluctuation of the temperature limit of supercooling in XPCs is influenced by intracellular substances in XPCs (Kasuga et al 2006;Kasuga et al unpublished). Supercooling capability of XPCs in beech is significantly reduced when the protoplasts are broken and the spaces within cell walls (previously occupied by protoplasts) are substituted with distilled water, suggesting an important role of original protoplast contents in supercooling (Kasuga et al 2006).…”

“…Supercooling capability of XPCs in beech is significantly reduced when the protoplasts are broken and the spaces within cell walls (previously occupied by protoplasts) are substituted with distilled water, suggesting an important role of original protoplast contents in supercooling (Kasuga et al 2006). It has also been shown that expression of some genes (Takata et al 2007), accumulation of some proteins (Arora et al 1992;Welling and Palva 2006) and accumulation of soluble sugars (Kasuga et al 2007a) are related to fluctuation of supercooling capability in XPCs, although the roles of changes in these components in supercooling are unclear.…”

“…It has also been shown that expression of some genes (Takata et al 2007), accumulation of some proteins (Arora et al 1992;Welling and Palva 2006) and accumulation of soluble sugars (Kasuga et al 2007a) are related to fluctuation of supercooling capability in XPCs, although the roles of changes in these components in supercooling are unclear. It is noteworthy that crude xylem extracts from several boreal hardwood species that contained deep supercooling XPCs exhibited high capability for promoting supercooling of water, indicating supercooling-facilitating (SCF) capability in xylem tissues (Kasuga et al 2006). Furthermore, analysis of crude xylem extracts from Cercidiphyllum japonicum (katsura tree) has revealed the presence of four kinds of SCF flavonol glycosides, which may have an important role in supercooling in XPCs (Kasuga et al 2008).…”

Change of supercooling capability in solutions containing different kinds of ice nucleators by flavonol glycosides from deep supercooling xylem parenchyma cells in trees

“…It has been shown that artificial release of intracellular substances from XPCs significantly reduced supercooling capability in beech XPCs [13]. It has also been reported that the fluctuations of supercooling capability in XPCs are associated with changes in expression of many genes in larch [20], changes in accumulation of many proteins in several trees [5] and changes in accumulation of soluble carbohydrates in birch [9], although the direct roles of these physiological changes in deep supercooling of XPCs remain to be clarified.…”

Characterization of Anti-Ice Nucleation Activity of the Extract from Coffee Refuse

“…Like hinokitiol, the materials with anti-ice nucleation activity play an important role of deep supercooling in the xylem parenchyma cells of coniferous trees Kasuga et al, 2006 . Moreover, four kinds of flavonol glycosides with anti-ice nucleation activity have an important role in supercooling in the xylem parenchyma cells of katsura trees Cercidiphyllum japonicum Kasuga et al, 2008 .…”