The State of Water and Cell Morphology In Deep Frozen Populus
The State of Water and Cell Morphology In Deep Frozen Populus
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Date
1985
Authors
Hirsh, Allen Gene
Advisor
Solomos, Theophanes
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Abstract
By using differential scanning calorimetry, electron microscopy, light
microscopy, and freezing survival experiments, it is shown that superhardy
Populus balsamifera v. Virginiana (Sarg.) is capable of withstanding liquid
nitrogen (LN 2) temperatures because of the formation during cooling, at a
temperature of about -30°C and cooling rates less than 30°C/hr, of aqueous
glasses in the intracellular solutions.
In more detail, the major findings concerning the state of intracellular
water are: (1) the bulk of the intracellular contents go through an equilibrium
glass transition at about -28°C during slow (<5°C/hr) cooling; (2)
smaller additional amounts of intracellular material go through equilibrium
glass transitions at about -47°C and -70°C; (3) as a result of the resistance
to homogeneous nucleation of these glass forming intracellular solutions when
they are in equilibrium with extracellular ice at<.-20°c, cooling/warming at
any combination of rates from 3°C/hr to 1200°C/min between -20°c and -196°C is
non-injurious to fully hardened wood; (4) death associated with quench cooling
in LN2 from -15°C is correlated with the devitrification, (cold
crystallization) near -90°C upon warming of the very low temperature glass
forming component, followed by further devitrification of the higher
temperature components, especially between -30°c and -20°c; and (5) the
vacuolar compartment appears least resistant to devitrification and capable of
thereby causing death even when the cytoplasm resists devitrification. In addition, it was found that when fully superhardy wood is cooled
slowly (3°C/hr) after being imbibed with water (doubling total water content)
massive intracellular freezing occurs. Despite the fact that total tissue
water of tender Populus (summer wood) is 2x that of the artifically water
loaded hardy wood on a gram H20/gram dry weight basis, tender wood cooled at
3°C/hr to -50°c does not display intracellular freezing. It is killed by
-2°C. It is shown that in both tender and hardy wood <10% of water is extracellular.
Thus a significant excess of extracellular water appears to cause
intracellular freezing and this may be a major reason for the large water loss
seen in the fall 'hardening off' of most temperature zone woody plants.
It is also shown that during slow cooling, the plasma membranes of both
hardy and tender Populus cells stick to and collapse the cell wall, but that
these membranes stay smooth in the case of superhardy cells and wrinkle
markedly in the case of tender cells. Membrane-associated particles appeared
to clump in the membranes of slowly cooled tender cells but not in the slowly
cooled hardy cells.