Isn't a reduction of water in the cells a big part of it- water expands and burst the cell walls is how I remember cold damage being caused, not about compounds that resist freezing being absent. Hardening is a dehydration process, I thought. Is this compound you call antifreeze a newer understanding?

Not a compound at all Hman, I have no understanding of the physiology of bud hardiness. Reduction of water sounds very plausible though. I just liked the concept of antifreeze, an accumulating, "factor" that leaves the bud as more warm temps. accumulate.

I believe that along with that reduction in water comes a greater concentration of dissolved solids which lowers the freezing point.

I believe murky is correct, but in addition, plants synthesize different compatible solutes (antifreeze) in response to cold. You can read a bit about the other changes that happen here:

http://www.plantphysiol.org/content/120/2/391.full

Here is a link that might be useful: freezing tolerance in plants

Freezing tolerance is not the same thing as seasonal hardening off of deciduous trees. I didn't think the article was very relevant to this specific topic, but maybe I'm missing something.

Poor old Arabidopsis, the lab rat of the plant kingdom.

The abstract seemed to be pointing to freezing tolerance in a more general application and not to bud hardiness but, maybe some of the changes mentioned like those in cell walls also are part of seasonal hardening off. My brain used to like to study scholarly articles like this stuff, now it's just tiring but interesting still.

In additon, the article gives me a little hope that the lettuce might have been altered by the last 20 hours of near freezing temps and survive tonight's predicted 28 deg.. Hope springs eternal!