Plants and the art of confusion: Dodders, (Z)-3-Hexenyl acetate, and general lack of consensus.



I read an article in Scientific American aptly named “What A Plant Smells” by Daniel Chamovitz.  The story was about the parasitic Dodder: a leafless, too-lazy-to-make-chlorophyll,  orange-coloured  vine that “sniffs out” healthy plants nearby in search of a host to latch onto.  It does this by detecting volatile compounds like beta-mycrene released by succulent tomatoes, which guides it towards the location of said tomato. Upon finding the first tomato leaf with its vine tip, the Dodder will feel around for the tomato’s stem, which it will wrap itself around, sucking out all its hard-earned glucose bling.  Talk about gold-digging and sticking it up to the man!  So, at first, I started to ask: what is the likely explanation why some plants evolved to be parasitic?  I mean, it’s so much easier to make your own energy, so why put the fate of your own survival on the small chance that you’ll find a suitable host before the food in your cotyledons run out?   It doesn’t make sense.

Then, I read further and found out that Dodders hate wheat.  It’s too good for it or something.  It won’t even touch it with a 10-foot-pole (ok, maybe it didn’t say that).  And I thought, ok…what’s wrong with wheat?  Apparently, although wheat has beta-mycrene (like the tomato does), it also has another volatile compound called (Z)-3-hexenyl acetate.  These types of compounds are generally called herbivore-induced Volatile Organic Compounds (VOCs) because it’s a defense mechanism against herbivore attacks.  So, my next question was: why can’t scientists engineer that stuff as a spray product to protect their crops from herbivores and Dodders?

So I searched for research articles about VOCs to see if it is currently being used as repellent (because they, the scientists, have probably thought of everything), and it turns out that not only these VOCs do repel herbivores…they attract them at the same time?!?  Now, that’s just crazy.  Why would plants release compounds that both attract AND repel?  Are they confused?  What’s the benefit of being eaten by one herbivore, but not the other?  I mean, I wouldn’t release a scent that says, “Vampires? yes, please…but absolutely NO Zombies!”

If you want to see it for yourself, here are links:

Prepare to be confused.