Trees have big channels full of sugar in their bark. This sugar would be a wonderful medium for bacteria. Redwoods and many other trees are very long lived - an individual can live for thousands of years. How do the trees prevent bacteria from evolving around their defenses and taking over their sugar supply?
Humans and other vertebrates match the evolutionary abilities of bacteria with an immune system capable of similar evolution and innovation - capable of matching the offensive capabilities of organisms with much shorter generation times. Plants have no such immune system - it is thought that they rely on antibacterial chemicals they make. Given that penicillin has been in use in humans for only a few decades and many of our bacteria are already immune to its effects, how does a redwood prevent bacteria from evolving resistance to the limited set of defensive chemicals it has?
It may be that redwoods and other similarly long lived plants have "immune systems" that operate by mechanisms different from ours, but like ours are able to adapt and evolve in step with their bacterial aggressors. The search for such an immune system might be like the search for life on other planets - it may be based on concentrations of sugars or salts, electrical charges, or other unusual methods. I propose that a series of experiments be undertaken - analagous to searching for life on Mars - but designed to better understand the immune systems of trees. Understanding of this sort is good in itself, and might translate into better treatments for diseases in crops and humans.-- bungston, Mar 04 2004 I don't know if there really is a mechanism that would have crossover potential for humans, but I would rather see funding go to ideas like this than to give to farmers to "not grow" crops. [+]-- Klaatu, Mar 04 2004 I've not thought much about plant immune systems before, but I'm not sure how much of a threat bacteria pose. I imagine there are physical barriers more than anything. Also, don't forget that not all bacteria are bad - all plants have a symbiotic relationship with mycorrhizal fungal and bacterial colonies which grow around the plant roots and mediate nutrient uptake. Nitrogen fixing plants, such as legumes and clover, have root nodules containing specific bacterial consortia which are able to fix atmospheric nitrogen into a plant available form. This is a fundamental process providing plant available nitrogen to all other plants.-- hazel, Mar 05 2004 Fetching my Bio 110 notes... Ah, here we go...
Basically, the phloem, which transports sugar and water, is a closed system. Sucrose is actively transported into phloem cells, and water only moves through by osmosis. Very, very few large proteins get in, much less an entire bacteria or virus. It is purely a mechanical defense; not chemical or immune-system related.
Nearly all plant diseases infest from the outside in (unlike animals with respiratory passages).-- obnoxious, Mar 05 2004 I can't believe that an immune system of only mechanical barriers could effectively protect over hundreds of years. Branches fall off in windstorms. Lightning blasts pieces off. Bears sharpen their clothes. Boneheads carve their initials. All these things breach mechanical defenses and expose the innards of a tree or other long-lived plant. No doubt the bark and other mechanical defenses protect to a large degree - just as our skin protects us. But sometimes the barbarians breach the gate. There must be something more.-- bungston, Mar 05 2004 " bears sharpen their clothes"? There are bears out there wearing pointy suits? RUN FOR YOUR LIVES!!! ( could'nt resist).-- python, Mar 05 2004 hmm. I guess sharp looking bears are good, if unintentional.-- bungston, Mar 05 2004 It sounds crazy Bungs, but it's pretty much true. If trees get sick they usually die. They don't have anything like Leukocytes.-- Madcat, Mar 05 2004 random, halfbakery