The cold damages plants in several ways. If severe, it damages some of the cellular internal membranes, causing phenolic compounds to leak out of the cell. The phenolic compounds oxidize when exposed to air, causing the damaged tissue to turn black. Slightly damaged plants might cup their leaves downward or wilt.

Cold produces many of the same stresses that are brought on by a prolonged drought. During a cold spell, a plant's ability to absorb or translocate water is severely reduced as its own cells function less efficiently at the lower temperatures.

Obviously, cold tolerance varies widely by species, but within species and even cultivars, genetics are a key factor in determining a plants resistance to cold stress.

Al

what biologically makes a plant cold sensitive at 55 degrees? Obviously not (H20) ice crystals since it is not cold enough to freeze in the plant. What substance in a plant has a freezing point of 55 degrees or makes the plant cold sensitive at 55 degrees? Do the phenolic compounds freeze at 55?

I would more readily venture along enzyme activity and membrane fluidity lines rather than phenolic compounds. Enzymes have very precise functions at physiological temperatures (between 8 and 35 degrees, more or less). At higher or lower temperatures these enzymes are not functional.
Other than that, a plants ability to survive cold but not freezing temperatures depends on the percentage of unsaturated fats and how well the plant can adjust its unsaturation. You can try this : put two bottles of oil in the fridge : one of peanut oil (with high degree of saturation) and the other of olive oil (high degree of unsaturation, choose and olive oil with max. linolenic or linoleic acid), and see which one becomes solid first. The same thing happens in the plasma membrane.

To add to what Nazanine said, which I totally agree with, materials don't simply freeze at 0. There is a steady decrease in mobility of all particles as the temperature drops. As nazanine said, plants that have evolved in tropical areas have a higher degree of compounds that are most mobile at the higher temperatures of that area, whereas plants from, say the tundra, would have a much higher degree of compounds able to retain their fluidity and mobility at the colder temperatures. As a result, a plant doesn't have to be in freezing temperatures to get cold damage.

You know what? I'm quite sick right now and on lots of drugs to get me better. Not quite sure if I'm coherent and I wonder if that post will even make sense tomorrow!

As I stated - my college degree is in science - I want to know the exact names of these enzymes / fats / phenolic compounds /etc. and the mechanism which makes a certain plant more cold hardy than others.

I know about fats and fat saturation - organic chemistry was a huge part of my major. Which fats or enzymes in plant tissue is more cold sensitive than others? I would prefer reading scientific technical papers although I haven't found any when doing a google search.

If you want specific answers and journal articles, then why don't you search through the databases...?

The majority of journal articles won't be on google. They're in expensive journals (as you likely already know if you're in science) which aren't usually floating around for free on google. You'll need access to databases and journals. Any decent university should have full access to every journal you need.

Maybe someone else will know the names off the top of your head. Otherwise, I wouldn't expect others to do intensive searching for me.

Excuse me? I was trying to explain and point you in the right direction, not knowing your level of education. If I wanted specific names of enzymes and biomolecules, I wouldn't post on an internet forum demanding specific answers; I'd find it myself. That's not kindergarten, dear. I didn't realize that not only are you incompetent, but you're bitter too. I'll go back to another forum, which isn't frequented by ignorant and demanding trolls.

Reinbeaux, you can start off by doing a search for degree of unsaturation of fatty acids in phospholipids (phosphatidylcholine for example as it is the major component in the plasma membrane, but search also for phosphatidylcholine , -ethanolamine , -inositol, -glycerol), in DDG (diacyldigalactosylglycerol), DGG (diacylgalactosylglycerol) (major components of the thylakoid membrane), SL or SQDG (sulfoquinovosyldiacylglycerol).
Also check for the degree of saturation or unsaturation of different membranes with these fatty acids : 16:0 and 18:0 ; 18:1 , 18:2 and 18:3 (others are a bit less important).
Lots and lots of research is done on tomato, tobacco and Arabidopsis about cold (sub zero) but as Catalina mentionned many articles are found in expensive journals. Plant Physiology journal however lets you access articles that are older than one year. So you can start from there. Very often as well you can send an email to the authors (if you cant access teh journal) and ask them for a copy.
As for the enzymes, all enzymes have a temperature range where they are functional. Perhaps you can look up different plant enzymes (phosphatases, kinases, etc.) and check the range at which they are functional as well as their functions.
HTH

Forgot : it seems that ABA has to do with cold acclimation too.

...I would prefer reading scientific technical papers although I haven't found any when doing a google search...
and ...I didn't realize we had to keep things at a kindergarten level so you could understand too....

Why not contact a professor at a local institution of higher learning to do your research for you or explain this in the scientic terms you seek since we are ever so obviously no up to your advanced level.
This is a forum for sharing-not for asking others to do intensive research (sspecially from someone who should have learned research techniques in their college science classes).

I am agree with catalina_101. I found her post to be informative. I have an extensive science background myself, but plants are a whole different world. If you want detailed scientific information, you need to go to your local university library & do the research. Internet material is not subject to review & many times is incorrect or questionable.

That reinbeaux z8 does the same thing over on the Florida forum. Asks about hurricanes than starts some drama.

Anyway, to the point. I actually grow a handful of ultra-tropicals and out of the ones I grow I have not had any ill effects from brief temperatures in the upper 40's or above if there are only a handful of nights at this temp and the day is fairly warm, at least sunny. As a plant exposed to some sunlight would likely be warmed by such it seems to encourage photosynthesis and thus prevent the slow decline some see in climates without warm periods in the winter (california vs. florida). I have been growing many tropicals for a while, mostly fruit trees but recently some palms and as a result over the years my level of adventure has increased. I have done some research indicating that Ca and Si may play a role in enhancing plant cold hardiness and I am in the process of exploring some fert. formulas to determine any potential for this to be fact.

If the plant stops photosynthesis due to low temperatures it would have to rely on whatever stored energy it has, also its ability to move water is reduced. As Si and Ca potentially play a role in membrane "strength" it seems a harmless theory to test. Also, Si has something to do with the way a plant deals with micronutrients, also in the way a plant deals with "toxic" metals, such as Al. The "brown spotting" due to chill injury has been reduced in plants given Ca. A Ca spray has been used on fruit to prevent such injury. Some are sure the brown spotting is due to the concentration of inorganic salts (some of the micronutrients)as they sequester in the same areas as the temperature falls thus causing tissue damage. Si, it is thought, acts to keep the cellular levels of micronutrients and other compounds more evenly spaced minimizing tissue damage due to the increased concentrations of the aforementioned elements.

While enzyme activity surely plays a role it is this activity which may act to prevent this damage at optimal temps, when these enzymes become inactive perhaps their action can in part be somewhat aped by the inorganic Ca and Si.

I grow mangosteen and breadfruit as two examples of ultra-tropicals. Mangosteen is much hardier than most believe, but breadfruit is a real challenge. The breadfruit starts to defoliate after about 2 nights in the low 40's, mangosteen just slows down. As long as both avoid prolonged low temps below this, both will generally do all right, although breadfruit may have to come back from below soil level.

As stated before drought tolerance and cold tolerance share some common traits. Both Ca and Si play a role in drought tolerance as well.

Alan

Alan, you are right about Ca, however I think that the 'other side' of Ca should be mentionned too. Ca is one of those nutrients that are needed in very small amounts. It is toxic to plant cells when in big quantity. Dicationic Ca binds to membranes and rigidifies them , but the problem is that once bound, there's no way of getting rid of it ! (you can eventually get rid of it by adding Na, but then you're not better off neither and you'll have to find a way to get rid of Na!)
Another way Ca acts in response to stress, both biotic and abiotic. Ca is a second messenger in cells and has different functions in plant cell signaling.
But physiologically speaking, Ca *per se* doesn't act to prevent from cold nor drought.

The idea is not that Ca actually prevents cold damage but that "fortifies" the cell wall. Si has been found to aid in the uptake of beneficial elements and aids the plant in dealing with those elements which may be toxic. It has been reasoned that it also aids in making cell walls stronger. Up to now I have read the works of others, I have designed an experiment to determine if any of this actually aids in preventing cold damage or allows plants to resist temperatures below what would normally be predicted. I hope to at least see if there is any improvement, if not I do not consider my trials to be a waste of time, even failure can be a valuable learning experience.

Also, drought tolerance and cold resistance have been linked in some plants and both Ca and Si have been suggested as elements which may aid in greater drought tolerance. It can't hurt to try.

I have a degree (B.S.) in biology and work as a chemist. I say this to clarify that I have a a real experiment planned, not some anecdotal rubbish which raises more questions than it answers.

Alan

I never said your experiment was rubbish ;)
I only wanted to say that effects of Ca on biological membranes is known. Ca rigidifies the plasma membrane. The problem I was pointing out to is that once bound to membranes, Ca sticks there. By doing so, it becomes toxic as it alters membrane transport in and out, interferes with signalling, etc. So although it strengthens the membrane, it becomes toxic at the same time :)

Nazanine, did not think you had said my experiment was rubbish, just thought I'd mention so if it goes well others can try to confirm results.

I know the effects of Ca on the membrane has been fairly well worked out, my interest is to really see what different levels may have on the entire plant, especially as related to cold tolerance. If I get any plants that die without exposure to cold, I'll have an idea as to why, i suppose. We'll see, it probably takes a pretty hefty amount of Ca to tox out. I saw a study involving Ca's effects on a few plants, but no references to a toxic effect.

Alan

Hey, don't scare me off this forum!! ( smiling -- )
I mostly lurk because I have no formal education in this area , my sciences are in the animal veterinary field, but find botany most fascinating.
Nazanine, the Jerusalem artichoke tubers you once sent me are alive and well- divided those multiple tubers again this year, no worry about their cold hardiness-
Faith

Inga, I told you they were going to grow like weeds !! See, I ran away from them and moved to France :)
Alan, I was talking about EXCESS amounts of Ca..
but you're right lots of reaserch has been done about Ca and cold tolerance, drought, heat tolerance, etc.
Naz

Nazanine, I was sure you meant excess, but I think excess would be less likely to have negative effects than say, way excess. I mean so much as to be ridiculous. Plus, I think the uptake is less than perfect so how the Ca is introduced, despite being in excess, would prevent the plant from actually getting a harmful dose. Also, I would like to see how much is too much as this might be useful. I have not seens any articles on horticultural calamities caused by Ca. (other than foliar burn, or setback from using calcium chloride). Keep up the feedback as I have found your insight useful.

Alan

Isn't there a searchable database of literature in the National Library, or some other repositiory.? For medicine there is, and I can't imagine there not being one for botany.

Nazanine how about you post the citation? I can find it through my university's connection to ejournal databases.

Alan and Catalina and for whoever is intersted, I can not send the article thru GW (can't attach) and I can not post it here (if any copyright etc. problems). Your emails don't show on your member pages, so if you want you can send me your emails and I,ll forward a copy.
Naz

I have two African Baobabs and was advised not to leave them out in temps under 50F. A couple of times i have accidentally left them out in high 40's with no ill effects. For the first 10 yrs of their lives they went dormant if they got too cool or when the days shortened. This year they seem more able to take the lower temps and have stayed active longer than past years. Also,though i know it's not a tropical plant at all, we've had ordinary annual sunflowers freeze solid and come back just fine, no visible damage once the leaves thawed out. Other sunflowers from the same seed batch, same time, froze and turned into "cooked spinach" appearance when they thawed. Seems there is variability between individual plants as well as species.

I thought I would post a picture of an ultra-tropical as it is the topic of the thread. This is a 4 yr old mangosteen.

Alan

{{gwi:433676}}

nice mangosteen Alan. I have noticed that many mangosteen seedlings seem to send out more than one tap root and their still extremely slow growers.

I was told that the seed was actually part of the mother plant, something like a potato; that´s why there are so many roots and if the seed is divided each segment will become a single plant, if well managed of course.