Imagine for a moment that you had to stand outside your house or apartment, without moving, all winter long…and that you were naked.
How long do you think you could last?
Not long, especially if the temperature went below freezing. And certainly not if the temperature went below 0o F (-18o C).
And even annual plants may have to withstand an early or late frost in order to complete their life cycles.
But, you may reply, plants are not warm-blooded organisms like mammals. What difference is it to them whether it’s cold or not?
How Cold Kills Plants
What happens if water freezes inside at plant?
At least a couple of things can happen…both bad for the plant.
The first, and likely lethal for the plant, is ice crystal formation inside cells. This has just about the same effect on a plant cell as the little alien chestburster did on the actor John Hurt in the movie Alien. (Sorry, but it’s an effective analogy.) It’s lethal.
If, however, the water freezes outside the cells, in the intercellular spaces, this may lead to the extreme desiccation of the plant. That is, it’s sort of the same as if the plant was drying out.
Other cold-temperature effects on plants include (1) decrease in enzyme activity and (2) changes in the fluidity of cellular membranes, both of which could severely harm plant cells, and, thus, the plant as a whole.
To answer this question we have to consider plants at the cellular level.
How do the cells of cold-tolerant plants survive sub-freezing temperatures, i.e., withstand dehydration and, more importantly at very low temperatures (below 0o F or -18o C) , avoid the formation of ice crystals in the cell?
1. Accumulation of solutes (sucrose, mainly, but also other organic compounds such as proline) by the cells to depress the freezing point of water (think salting ice on the sidewalk) and to stabilize membranes. (But this can only be effective at temperatures from 32o F to 20o F.)
2. So-called “antifreeze” proteins help prevent ice crystals from forming in the extracellular spaces (outside cell); plant cells that make these proteins typically secrete them into cell wall region (intercellular spaces).
3. The plant cells may synthesize proteins called “dehydrins”, which are inside the cell (cytoplasm), may bind water molecules and alter the collective structure of water in the cell to stabilize membranes.
4. Plant cells can alter lipid composition of cellular membranes in order to adjust the fluidity (functionality) to colder temperatures.
A silly question? I think not.
Some unusual plants, by partially uncoupling their cellular mitochondria, can generate small amounts of heat. (Please see ref #1 below for more information) But this is likely not very significant with regard to cold tolerance, however. (More on this interesting topic here.)
Bottom Line: Plant cells survive sub-freezing temperatures by adjusting their solutes, proteins, and membrane lipids in order to withstand desiccation and to avoid ice crystal formation.
1. Seymour, Roger S. (1997) “Plants That Warm Themselves.” Scientific American, March 1997, pp. 104-109. (Full Text – PDF)
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