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How do cold weather plants survive freezing?
I'm trying to understand better how plants survive the winter in
cold climates. I know about leaf abscision, annuals and perennials, the withdrawal of sugars into storage roots, reduction in metabolic and growth rates, etc., but I don't understand how plants avoid or survive the destructive effects of freezing water in the cells. If I've got the numbers right, ice is about 9% less dense than liquid water. I would think that ice crystals, as they form, would rupture membranes and cell walls, causing irreverible damage to the cells. Isn't this what happens to animal tissue when it is frozen? As we have seen in the news, this is a problem for fruit trees in California and Florida - with freezing destroying the fruits and, if it gets cold enough, the trees. But how do cold weather plants handle it? Do cold weather plants continue metabolism and generate enough internal heat to keep from freezing? Do they manage to expel enough water that freezing is not a problem? Do they have cell walls that are tough enough to contain the freezing water by compression and prevent crystalization (i.e., leading to "supercooled" water)? Thanks. Alan |
#2
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How do cold weather plants survive freezing?
"Alan Meyer" schreef
I'm trying to understand better how plants survive the winter in cold climates. *** Anti-freeze PvR |
#3
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How do cold weather plants survive freezing?
"P. van Rijckevorsel" wrote in message ... "Alan Meyer" schreef I'm trying to understand better how plants survive the winter in cold climates. *** Anti-freeze PvR Now why didn't I think of that? Actually, I could see that there could be something to this. If the plant synthesizes alcohols or other low freezing point liquids that are dissolved in the cytosol, that would significantly lower freezing point - assuming the plant could tolerate it. It would also be relevant to know how the freezing point of the cytosol is affected by all of the solutes since any solution should have a lower freezing point than pure water. However it would be awfully useful if someone who actually knows the answer were to chime in. Alan |
#4
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How do cold weather plants survive freezing?
In article ,
Alan Meyer wrote: I'm trying to understand better how plants survive the winter in cold climates. I know about leaf abscision, annuals and perennials, the withdrawal of sugars into storage roots, reduction in metabolic and growth rates, etc., but I don't understand how plants avoid or survive the destructive effects of freezing water in the cells. There are several methods. If I've got the numbers right, ice is about 9% less dense than liquid water. I would think that ice crystals, as they form, would rupture membranes and cell walls, causing irreverible damage to the cells. Isn't this what happens to animal tissue when it is frozen? Yes, that happens to plant cells too. It's a sad sight when an unexpected frost turns your frost-sensitive garden plants into soggy dripping rags. As we have seen in the news, this is a problem for fruit trees in California and Florida - with freezing destroying the fruits and, if it gets cold enough, the trees. But how do cold weather plants handle it? Do cold weather plants continue metabolism and generate enough internal heat to keep from freezing? Do they manage to expel enough water that freezing is not a problem? Do they have cell walls that are tough enough to contain the freezing water by compression and prevent crystalization (i.e., leading to "supercooled" water)? The usual method is to dry out the exposed tissues so that the solute concentration in the cells increases enough to lower the freezing point. This method is used by evergreen trees and many other plants. It can be quite visible. For example, I've got some Opuntia cacti that are native to Ontario. When the days get short, despite the rains, they shrivel up their pads and let them droop until they are flat on the ground. They benefit from the insulating property of snow cover this way, too. Some plants enhance this anti-freeze effect by specifically increasing some solute, usually sugar, as well. Some vegetables, such as brussels sprouts, are well-known to taste sweeter after a hard frost. Another method is to force water out of the cells and into the spaces between them where it can freeze without rupturing the cells. The leaves may appear frozen, with the characteristic dark, glassy look, and may even droop pitifully. However, they go back to normal when the temperature rises. I've observed this in brassicas, leeks, and a number of evergreen perennials and weeds. Apart from the spring shoots of skunk cabbage (an aroid) there aren't many plants that can generate much heat from metabolism, and certainly not all winter. I don't know about cell walls that can compress water so well as to prevent freezing. It's risky to say anything is impossible in biology! Note also that a lot of plants that don't freeze in warmer climates can take a lot of damage, even freezing to the ground, and still come back year after year. I'm always surprised when I read British garden books that plants I think of as herbaceous perennials don't die to the ground in winter there. |
#5
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How do cold weather plants survive freezing?
"Alan Meyer" schreef
Now why didn't I think of that? Actually, I could see that there could be something to this. If the plant synthesizes alcohols or other low freezing point liquids that are dissolved in the cytosol, that would significantly lower freezing point - assuming the plant could tolerate it. It would also be relevant to know how the freezing point of the cytosol is affected by all of the solutes since any solution should have a lower freezing point than pure water. However it would be awfully useful if someone who actually knows the answer were to chime in. *** Actually, I am not yoking. It is not necessary: truth is stranger than fiction. One such usage of anti-freeze is that some evergreens use monosaccharides instead of disaccharides: this lowers the freezing point of the leaves. PvR |
#6
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How do cold weather plants survive freezing?
wrote in message . .. In article , Alan Meyer wrote: I'm trying to understand better how plants survive the winter in cold climates. ... bae and pvr, Thank you both for your explanations. I presume that with a sufficiently lowered freezing point in the plant cells, it might also be possible to carry on at least a tiny amount of metabolic activity - which might help repair damage during the winter. Alan |
#7
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How do cold weather plants survive freezing?
Here's a review on plant cold acclimation. There are recent articles
listed at the bottom. Thomashow, M.F. 2001. So What's New in the Field of Plant Cold Acclimation? Lots! Plant Physiology 125: 89-93. http://www.plantphysiol.org/cgi/content/full/125/1/89 David R. Hershey |
#8
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How do cold weather plants survive freezing?
On Jan 30, 3:01 pm, " wrote:
Here's a review on plant cold acclimation. There are recent articles listed at the bottom. Thomashow, M.F. 2001. So What's New in the Field of Plant Cold Acclimation? Lots! Plant Physiology 125: 89-93.http://www.plantphysiol.org/cgi/content/full/125/1/89 David R. Hershey Interesting article. bae mentioned in his response three techniques plants use: dehydration moving water to intercellular spaces increasing solute concentration, for example by storing monosacharides in place of disacharides. One more technique identified in the article was expression of a polypeptide that decreased "the propensity of membranes to form deleterious hexagonal II phase lipids upon freeze-induced dehydration". Just think what Lysenko would have given to know about all this :^) Thanks. Alan |
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