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  #1  
Old 11-16-2007, 04:33 PM
levdrakon levdrakon is offline
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What makes a frost hardy plant frost hardy?

Or cold hardy?

I know for many plants it depends on acclimation, but for many plants no amount of acclimation will help. The first light frost, they turn to mush.

Other plants, properly acclimated, can survive varying degrees of freeze. Light freeze? No prob. Deep hard freeze, uh-oh.

Some plants seem to take significant damage from very cold, but not freezing temperatures.

What are the exact physiological and biochemical differences among plants with different degrees of frost hardiness?

For instance, my basil must be a tropical plant as it instantly turned to mush when the temps dropped just below freezing. But my hollyhocks, columbines and freesias all just laughed. It's not cold!

Some tropical plants like my hoya vines seem able to handle light frosts if they're acclimated, though they'd never take a hard freeze.

What exactly is going on inside plants? Is it a particular chemical? Some physical difference in plant cell walls which resists damage? Water expands when it freezes. This destroys typical cells. In plants which can resist frost, is the water inside the cells just not freezing? Some natural anti-freeze chemical? Or is the water freezing but the cell walls can somehow handle it?

Plant geneticists are getting better and better at engineering plants. Is cold hardiness something geneticists could easily transfer from a cold hardy plant to a non-cold hardy plant? With a little genetic tweaking, could I leave my African Violets outside in a frost?
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  #2  
Old 11-16-2007, 05:57 PM
Chez Guevara Chez Guevara is offline
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Quote:
Originally Posted by levdrakon
What exactly is going on inside plants? Is it a particular chemical? Some physical difference in plant cell walls which resists damage? Water expands when it freezes. This destroys typical cells. In plants which can resist frost, is the water inside the cells just not freezing? Some natural anti-freeze chemical? Or is the water freezing but the cell walls can somehow handle it?
I'm more than interested in this subject and hopefully this source can start the ball rolling.

Quote:
The key to frost-hardiness is the avoidance of intracellular freezing and some plants are remarkably effective in achieving this. One of the ways in which the freezing point of plant sap may be depressed is by the accumulation of solutes (cf. the use of 'anti-freeze' in water-cooled automobile radiators

An alternative explanation of frost tolerance is that a higher proportion of the water in hardy plants is bound to cell constituents and so does not freeze as readily as that in tender plants where it is mainly in a free state

Some plants are able either to suppress the formation of ice crystals (supercooling), or at least keep them in the cell walls and prevent them from entering the living part of the cell (the cytoplasm and nucleus).
The solutes are sugars present in the plant cells.

If anyone can expand on this explanation (or debunk it) then please go ahead.
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Old 11-19-2007, 11:01 AM
Chez Guevara Chez Guevara is offline
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Quote:
Originally Posted by levdrakon
Plant geneticists are getting better and better at engineering plants. Is cold hardiness something geneticists could easily transfer from a cold hardy plant to a non-cold hardy plant? With a little genetic tweaking, could I leave my African Violets outside in a frost?
Bump.
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  #4  
Old 11-19-2007, 11:40 AM
Santo Rugger Santo Rugger is offline
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Does it have anything to do with the phenomenon that saturated fats are solid at room temperature, because they occur naturally in plants that are usually 85F or so?
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Old 11-19-2007, 09:55 PM
elelle elelle is offline
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It's not a simple an issue of freezing water in plant cells bursting, but that's a start.

When plants hit the freezing temperatures of approaching winter, they have already had many signals to induce dormancy, cooler temps, as well as shorter daylight time. This starts a physiological and metabolic cascade of adjustment, in order to survive the coming cold. It's not absolutely understood, but here are the basics, as I understand it.( I'm not a biochemist, so if one could chime in for clarity, most welcomed.)

The plant, if acclimated to it's environment, starts to produce hormones, and other biochemicals, signalling dormancy. In plants not acclimated, a simple freeze will cause the plant to die due to ice crystals forming intracellularly, which compromise the cell walls of the plant. It's not a simple case of freezing there, either; often, the cells themselves might not have frozen, but the initial freeze will have compromised the cell walls, and, when warming back up, osmosis causes a state of extreme dehydration, which kills the plant.

In plants that are cold hardy, they have evolved some wonderful measures to avoid that death. And, multiple mechanisms are at work. In order to avoid the cellular explosion of killing freeze, plants modulate that effect by utilising sugar solutes in their cells to avoid the exploding osmosis effect. It helps them to support cellulaur membrane stability. There is good evidence that they also utilise lipids in reinforcing their cell membranes to prevent a breach, allowing for a greater expansion after frost.

One plant hormone that has been thought to help with the whole dormant phase is abscisic acid.But, there is a whole lot of metabolic action that is not yet understood. I've read some theories on calcium metabolites, and specific proteins, but, it's in the process of understanding.

One nice observation I've had, the past year, as a horticulturist, is a Freeze is not necessarily a Freeze. This last April, we had a rare three day spring four day nights of freezing temps. I got to the nursery and expected to see a bad mayhem of conked out plants. Nope. The native plants that I grow were all still sporting their new growth quite well. The asian plants that evolved in temperate climes, not adapted to the local environment, were all hit hard, and frozen. If it were the same type of Fall freeze, all the plants would have been hit hard. But, due to their complicated hormones wanting to grow then, they survived just fine.

I am constantly amazed at the complexity of plant survival.

Last edited by elelle; 11-19-2007 at 09:59 PM..
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  #6  
Old 11-19-2007, 11:42 PM
Der Trihs Der Trihs is offline
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Quote:
Originally Posted by Santo Rugger
Does it have anything to do with the phenomenon that saturated fats are solid at room temperature, because they occur naturally in plants that are usually 85F or so?
My memory is vague on this, but as I recall, that's part of the problem. IIRC, plants that evolved in always-warm climates use such fats for various purposes, as they take less energy to make than the alternatives. When it gets cold, they don't work properly and the plant dies. Plants from cold climates uses different substances that take more energy to make, but work in colder temperatures.
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