X-Message-Number: 23638
From: "Basie" <>
Subject: The single most important cause of freezing-damage 
Date: Mon, 15 Mar 2004 22:46:27 -0500

I read this article. It seems the idea that ice crystals cut up membranes is
not true.
The single most important cause of freezing-damage is when this dehydration
exceeds what cells can tolerate. In freezing-adapted species, lethal
freezing-induced dehydration causes damage to cell membranes.
A better strategy may be to confer tolerance of cellular dehydration.
REVIEW
Plant Freezing and Damage
Roger S. Pearce+
Department of Biological and Nutritional Sciences, The University of
Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK

Received: 24 February 2000 ; Returned for revision: 9 May 2000 . Accepted:
22 November 2000

Imaging methods are giving new insights into plant freezing and the
consequent damage that affects survival and distribution of both wild and
crop plants. Ice can enter plants through stomata and hydathodes. Intrinsic
nucleation of freezing can also occur. The initial growth of ice through the
plant can be as rapid as 40 mm s-1, although barriers can limit this growth.
Only a small fraction of plant water is changed to ice in this first
freezing event. Nevertheless, this first rapid growth of ice is of key
importance because it can initiate further, potentially lethal, freezing at
any site that it reaches. Some organs and tissues avoid freezing by
supercooling. However, supercooled parts of buds can dehydrate
progressively, indicating that avoidance of freezing-induced dehydration by
deep supercooling is only partial. Extracellular ice forms in
freezing-intolerant as well as freezing-tolerant species and causes cellular
dehydration. The single most important cause of freezing-damage is when this
dehydration exceeds what cells can tolerate. In freezing-adapted species,
lethal freezing-induced dehydration causes damage to cell membranes. In
specific cases, other factors may also cause damage, examples being cell
death when limits to deep supercooling are exceeded, and death of shoots
when freezing-induced embolisms in xylem vessels persist. Extracellular
masses of ice can damage the structure of organs but this may be tolerated,
as in extra-organ freezing of buds. Experiments to genetically engineer
expression of fish antifreeze proteins have not improved freezing tolerance
of sensitive species. A better strategy may be to confer tolerance of
cellular dehydration.Copyright 2001 Annals of Botany Company


Freezing, dehydration, infrared video thermography, low temperature scanning
electron microscopy, NMR micro-imaging

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