Reposted and slightly modified from Classic DigitalBio.
Some people say that science takes the magic out of everyday life.
I've learned some things by reading Science (1) that might give some people nightmares, especially young children. Remember that scene in "The Wizard of Oz" when the trees get ticked off and start hurling apples at poor Dorothy?
Real plants do defend themselves.
Those "Wizard of Oz" trees would really defend themselves by giving poor Dorothy a tummy ache
Pardon me a moment while I apologize to enforcers of precise scientific language.
Okay, okay, real apple trees probably wouldn't hurt poor Dorothy. After all, apple trees benefit by making fruit that kids like Dorothy want to eat. This has an evolutionary benefit because Dorothy would eat the apples and (in the pre-indoor plumbing days) would deposit the seeds in a nice rich pile of human fertilizer after her body was done with them. Real trees would probably only fight back if Dorothy chomped a bit on the leaves and bark.
Nevermind, this is even better. Trees "talk" to each other.
We learned earlier that plants move more than you think, but they probably don't communicate through dance. Even if a tree waved its branches frantically around, the other trees wouldn't see it. After all, they don't have any eyes. (Well, someone had to say it.)
But trees have other abilities that we don't see.
Trees (and other plants) can communicate by passing gas. You may not have gotten the point, but you've probably received some of the messages.
For example, if you walk around on the Berkeley, CA, campus, you know there are Eucalyptus trees around. You can't escape the smell. (The first time I visited, I thought someone must really be into cough-drops.)
Eucalyptus trees make over 30 volatile compounds (2) that contribute to that unusual smell. At least some of those compounds are messages to other trees. And a pine forest, what is that saying?
This first time I heard this fanciful idea of trees talking to each other was when I was in graduate school. This was back in the days when we had to walk five miles in the snow to get to the lab (Oops, wrong story!).
One of the students and a post-doc in our lab made subtractive cDNA libraries to try and find wound-inducible genes. They were hoping to find some of the genes for making those tree-talking molecules, but their tools were a bit too crude.
Science magazine contains some great articles that describe more recent experiments showing that the talking tree hypothesis is correct, at least for a few plants.
Baldwin et. al. describes some wonderful experiments where researchers observed that tobacco plants get eaten less when they live near sagebrush. Using microarray technology and sensitive analytical instruments, they found that the sagebrush produced all kinds of volatile compounds that traveled through the air. They also found that nearby tobacco plants responded by turning on new genes.
When tobacco plants heed the warning, they make a proteinase inhibitor. Since the proteinase inhibitor makes it harder to digest protein, the leaf-eating animals probably feel a bit ill after chewing those tobacco plants. Maybe they swear off chewing tobacco for good! Or maybe they decide that next time, they'll try a different brand.
Whatever goes through the murky minds of the herbivores:
When sagebrush talks, tobacco listens.
1. Baldwin IT, Halitschke R, Paschold A, von Dahl CC, Preston CA. Volatile Signaling in Plant-Plant Interactions: "Talking Trees in the Genomics Era." 2006. Science. 311:812-5.
2. Zini CA, Zanin KD, Christensen E, Caramao EB, Pawliszyn J. Solid-phase microextraction of volatile compounds from the chopped leaves of three species of Eucalyptus. 2003. J Agric Food Chem. 51:2679-86.
Airborne volatiles are used against virus infection by inducing the hypersensitive response in plants too:
Shulaev, V. et al. Airborne signalling by methyl salicylate in plant pathogen resistance. Nature 385: 718-721, 1997.
I just thought I would drop a note - apple seeds aren't very likely to be dropped in a pile of our feces considering that we don't eat the cores - but I know the sheep I used to raise gobbled them up. No doubt, apples like other fruits evolved to be be eaten and fertilized for free, although today we do them the favor of propagating them vegitatively instead of eating their seeds. Maybe the apple trees knew that Dorothy wouldn't plant their seeds, and so that's why they were mad at her?
AJ: Thanks for the reference! That sounds really interesting.
IM: Horses eat apple cores and deposit the seeds in nice piles of fertilzer, but I guess there aren't many humans who would. I agree with you, maybe this is why the trees were so mad!
There's a really wonderful book by Michael Pollan called "The Botany of Desire: A Plant's Eye View of the World" that looks at the relationship between humans and apples, tulips, marijuana, and potatoes. From the Editorial Review on amazon.com:
[Pollan] uses the history of John Chapman (Johnny Appleseed) to illustrate how both the apple's sweetness and its role in the production of alcoholic cider made it appealing to settlers moving west, thus greatly expanding the plant's range. He also explains how human manipulation of the plant has weakened it, so that "modern apples require more pesticide than any other food crop."
The book is a great read, and gives an interesting perspective on how plants communicate with us or take advantage of the things we desire - e.g. sweetness, beauty, intoxication, control.
This is entirely speculation, but I think the most common ways of selecting - and fostering - new species of apples, have been through grafting - which is pretty widely used, and planting apple seeds.
I don't think humans have, to date, been able to clone or genetically engineer apple trees.
But, my information is based on a lecture by someone who had been trying to clone apples for his post-doc research, and this was a few years ago. So maybe I've missed something.