Supercooling of xylem ray parenchyma cells in tropical and subtropical hardwood species |
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Authors: | Katsushi Kuroda Jun Ohtani S Fujikawa |
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Institution: | (1) Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan, JP;(2) Institute of Low Temperature Science, Hokkaido University, Sapporo 060, Japan Fax: 81-011-706-7142; e-mail: sfuji@pop.lowtem.hokudai.ac.jp, JP |
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Abstract: | The freezing behavior of xylem ray parenchyma cells in several woody species, Ficus elastica, F. microcarpa, Mangifera indica, Hibiscus Rosa-sinensis, and Schefflera arboricola, that are native to non-frost tropical and subtropical zones, was investigated by differential thermal analysis (DTA), cryo-scanning
electron microscopy (cryo-SEM) and freeze-replica electron microscopy. Although profiles after DTA did not exhibit clear evidence
of supercooling in the xylem ray parenchyma cells, electron microscopy revealed that the majority of xylem ray parenchyma
cells in all of the woody species examined were supercooled to around –10°C upon freezing temperatures and were not frozen
extracellularly. It seems likely that DTA failed to reveal the low temperature exotherm (LTE), that is produced by breakdown
of supercooling in the xylem ray parenchyma cells as a consequence of the overlap between the high temperature exotherm and
the LTE in each case. The xylem ray parenchyma cells in these woody species were very sensitive to dehydration, and supercooling
had, to some extent, a protective effect against freezing injury. It is suggested that the capacity for supercooling of xylem
ray parenchyma cells of tropical and subtropical woody species might be the result of inherent structural characteristics,
such as rigid cell walls and compact xylem tissues, rather than the result of positive adaptation to freezing temperatures.
The present and previous results together indicate that the responses of xylem ray parenchyma cells in a wide variety of hardwood
species to freezing temperatures can be explained as a continuum, the specifics of which depend upon the temperatures of the
growing conditions.
Received: 24 January 1997 / Accepted: 13 May 1997 |
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Keywords: | Supercooling Intracellular freezing Tropical and subtropical woody plants Xylem ray parenchyma cells Cryo-scanning electron microscopy |
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