I have seen this assertion many times and it was repeated by a friend last night: tropical plants will likely die at less than 55 degrees F. Can someone please tell me what is the mechanism? What causes death?
I would think that 55 would still be a bit high, considering... Generally, though, they are just too specialised in thier environment to handle anything too far outside of it. Even humidity can be a factor in the same regard.
Thanks for the response, but I'm looking for a more specific answer. What are the biochemical, physiological or other mechanisms for tropical plant death below 55 degrees F? Freezing causes all kinds of trouble when cells are destroyed by expanding ice crystals. Their formation may be delayed by a particular plant's chemical makeup that inhibits ice crystals a bit. Whar is the analogous mechanism for tropicals?
Well, freezing in tropicals might not kill them if the humidity is high - I certainly have had the experience where, growing them in the desert, they die at 55F. However, at 55F in humid environments they do just fine. I think it has something to do with the heat-exchange mechanism in tropical plants - they are really really well adapted to dispersing heat, rather than retaining it. So, when environmental temperatures drop below the acceptable heat-exchange levels for the plant in question, it continues to let off its own heat, until such point as it hasn't got any energy left to sustain itself. Then it freezes.
Hi Linda, I think that the answer relates to the process of photosynthesis in the chloroplasts in the green cells. This process, the most fundamental for all plants, occurs in the lipid (fatty) membranes of the chloroplast. These membranes have high levels of unsaturated fatty acids (like the polyunsaturated fats we are all supposed to eat). Typically, two particular fatty acids 18:3 alpha linolenic acid and 16:3 hexadecatrienoic acid make up 2/3rds of the fat in the membranes. When plants are genetically modified to contain more or less of these two fats, both the high and low temperature tolerance of the plants can be altered. From this, I imagine that tropical plants have a specific fatty acid content adapted to the temperature regime they normally encounter. When the temperature is outside this range, they are mal-adapted, photosynthesis fails....plant weakens ...plant dies. Ciao BrianO
Many thanks to Lorax and bjo. Those are two credible possibilities. I'm going to see if I can get in touch with plant physiologists at UC Berkeley or UC Davis for more ideas. Linda
