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RE: Tt: RE: fall colors - not always as it seems.
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I'm in the middle of a Plant Stress Physiology class, so I'll put in my
2 cents worth.
Intracellular freezing kills plant cells, so some plants have
adaptations that allow them to survive constant temperatures below 0
degrees C. However, even the most hardy plants need a period of
acclimation at colder, non-freezing temperatures in order to
'cold-harden'. Some plants never acclimate and will die at below
freezing temperatures. Other plants deep-supercool; ice formation is
prevented somehow by the suppression of heterogeneous ice nucleation at
below freezing temperatures. Spontaneous, or homogeneous ice nucleation
occurs at -40 and this temperature is the theoretical lower bound for
the survival of plants with this mechanism. Most of these plants will
not deep-supercool to anywhere near -40, however. I'm not too clear as
to how the plants do this, but a number of low temperature induced genes
have been identified during cold acclimation that may encode protiens
involved in this. Another strategy used by the most hardy of plants
does not involve deep supercooling. They seem to rely on a
reorganization of the structure of individual cells - an increase in
endoplasmic reticulum structures, for example - and the breakdown of
starches into sucrose. This seems to me like some sort of programmed
desiccation of the cell that removes intracellular water from being
available for freezing. A lot of the research has been done on Poplars
and Dogwoods, both genuses containing species that are hardy down to
temperatures below -40.
There is much more happening at low temperature in plants than I have
time for, but there is a lot of literature out there on both freezing
stress and chilling stress.
One place to start is:
http://www.hort.purdue.edu/cfpesp/cfpesp.htm
> ----------
> From: Gary Letteron[SMTP:glue39@mail.bcpl.lib.md.us]
> Reply To: Community_Forestry
> Sent: Wednesday, October 15, 1997 5:53 PM
> To: Community_Forestry
> Subject: Re: Tt: RE: fall colors - not always as it seems.
>
>
> ----------------------------------------------------------------------
> -
> Hi!
>
> The Larch is not the only conifer that looses it needles before
> winter. I
> can add two to your list: Bald Cypress and Dawn Redwood...
>
> I am not qualified to answer the question about what evergreens do in
> the
> winter. ...But, my understanding is this --everybody feel free to
> contradict me-(-: They push extra nutrients up into the needles for
> the
> winter then shut down production (maybe in the reverse order).
> Meanwhile,
> they can die for lack of water when the temperature gets above
> freezing,
> usually due to high winds. Soooo, it might be a good idea to water
> your
> fresh evergreen transplants during warm spells in the winter.
>
> Hope this helps,
>
> -=G=-
>